This patchset is being developed here: https://github.com/cyphar/linux/tree/resolveat/master
Patch changelog: v11: [RESEND: https://lore.kernel.org/lkml/20190728010207.9781-1-cyphar@cyphar.com/] * Fix checkpatch.pl errors and warnings where reasonable. * Minor cleanup to pr_warn logging for may_open_magiclink(). * Drop kselftests patch to handle %m formatting correctly, and send it through the kselftests tree directly. [Shuah Khan] v10: https://lore.kernel.org/lkml/20190719164225.27083-1-cyphar@cyphar.com/ v09: https://lore.kernel.org/lkml/20190706145737.5299-1-cyphar@cyphar.com/ v08: https://lore.kernel.org/lkml/20190520133305.11925-1-cyphar@cyphar.com/ v07: https://lore.kernel.org/lkml/20190507164317.13562-1-cyphar@cyphar.com/ v06: https://lore.kernel.org/lkml/20190506165439.9155-1-cyphar@cyphar.com/ v05: https://lore.kernel.org/lkml/20190320143717.2523-1-cyphar@cyphar.com/ v04: https://lore.kernel.org/lkml/20181112142654.341-1-cyphar@cyphar.com/ v03: https://lore.kernel.org/lkml/20181009070230.12884-1-cyphar@cyphar.com/ v02: https://lore.kernel.org/lkml/20181009065300.11053-1-cyphar@cyphar.com/ v01: https://lore.kernel.org/lkml/20180929103453.12025-1-cyphar@cyphar.com/
The need for some sort of control over VFS's path resolution (to avoid malicious paths resulting in inadvertent breakouts) has been a very long-standing desire of many userspace applications. This patchset is a revival of Al Viro's old AT_NO_JUMPS[1,2] patchset (which was a variant of David Drysdale's O_BENEATH patchset[3] which was a spin-off of the Capsicum project[4]) with a few additions and changes made based on the previous discussion within [5] as well as others I felt were useful.
In line with the conclusions of the original discussion of AT_NO_JUMPS, the flag has been split up into separate flags. However, instead of being an openat(2) flag it is provided through a new syscall openat2(2) which provides several other improvements to the openat(2) interface (see the patch description for more details). The following new LOOKUP_* flags are added:
* LOOKUP_NO_XDEV blocks all mountpoint crossings (upwards, downwards, or through absolute links). Absolute pathnames alone in openat(2) do not trigger this.
* LOOKUP_NO_MAGICLINKS blocks resolution through /proc/$pid/fd-style links. This is done by blocking the usage of nd_jump_link() during resolution in a filesystem. The term "magic-links" is used to match with the only reference to these links in Documentation/, but I'm happy to change the name.
It should be noted that this is different to the scope of ~LOOKUP_FOLLOW in that it applies to all path components. However, you can do openat2(NO_FOLLOW|NO_MAGICLINKS) on a magic-link and it will *not* fail (assuming that no parent component was a magic-link), and you will have an fd for the magic-link.
* LOOKUP_BENEATH disallows escapes to outside the starting dirfd's tree, using techniques such as ".." or absolute links. Absolute paths in openat(2) are also disallowed. Conceptually this flag is to ensure you "stay below" a certain point in the filesystem tree -- but this requires some additional to protect against various races that would allow escape using "..".
Currently LOOKUP_BENEATH implies LOOKUP_NO_MAGICLINKS, because it can trivially beam you around the filesystem (breaking the protection). In future, there might be similar safety checks done as in LOOKUP_IN_ROOT, but that requires more discussion.
In addition, two new flags are added that expand on the above ideas:
* LOOKUP_NO_SYMLINKS does what it says on the tin. No symlink resolution is allowed at all, including magic-links. Just as with LOOKUP_NO_MAGICLINKS this can still be used with NOFOLLOW to open an fd for the symlink as long as no parent path had a symlink component.
* LOOKUP_IN_ROOT is an extension of LOOKUP_BENEATH that, rather than blocking attempts to move past the root, forces all such movements to be scoped to the starting point. This provides chroot(2)-like protection but without the cost of a chroot(2) for each filesystem operation, as well as being safe against race attacks that chroot(2) is not.
If a race is detected (as with LOOKUP_BENEATH) then an error is generated, and similar to LOOKUP_BENEATH it is not permitted to cross magic-links with LOOKUP_IN_ROOT.
The primary need for this is from container runtimes, which currently need to do symlink scoping in userspace[6] when opening paths in a potentially malicious container. There is a long list of CVEs that could have bene mitigated by having RESOLVE_THIS_ROOT (such as CVE-2017-1002101, CVE-2017-1002102, CVE-2018-15664, and CVE-2019-5736, just to name a few).
And further, several semantics of file descriptor "re-opening" are now changed to prevent attacks like CVE-2019-5736 by restricting how magic-links can be resolved (based on their mode). This required some other changes to the semantics of the modes of O_PATH file descriptor's associated /proc/self/fd magic-links. openat2(2) has the ability to further restrict re-opening of its own O_PATH fds, so that users can make even better use of this feature.
Finally, O_EMPTYPATH was added so that users can do /proc/self/fd-style re-opening without depending on procfs. The new restricted semantics for magic-links are applied here too.
In order to make all of the above more usable, I'm working on libpathrs[7] which is a C-friendly library for safe path resolution. It features a userspace-emulated backend if the kernel doesn't support openat2(2). Hopefully we can get userspace to switch to using it, and thus get openat2(2) support for free once it's ready.
Cc: Al Viro viro@zeniv.linux.org.uk Cc: Eric Biederman ebiederm@xmission.com Cc: Andy Lutomirski luto@kernel.org Cc: David Howells dhowells@redhat.com Cc: Jann Horn jannh@google.com Cc: Christian Brauner christian@brauner.io Cc: David Drysdale drysdale@google.com Cc: Tycho Andersen tycho@tycho.ws Cc: Kees Cook keescook@chromium.org Cc: Linus Torvalds torvalds@linux-foundation.org Cc: containers@lists.linux-foundation.org Cc: linux-fsdevel@vger.kernel.org Cc: linux-api@vger.kernel.org
[1]: https://lwn.net/Articles/721443/ [2]: https://lore.kernel.org/patchwork/patch/784221/ [3]: https://lwn.net/Articles/619151/ [4]: https://lwn.net/Articles/603929/ [5]: https://lwn.net/Articles/723057/ [6]: https://github.com/cyphar/filepath-securejoin [7]: https://github.com/openSUSE/libpathrs
Aleksa Sarai (8): namei: obey trailing magic-link DAC permissions procfs: switch magic-link modes to be more sane open: O_EMPTYPATH: procfs-less file descriptor re-opening namei: O_BENEATH-style path resolution flags namei: LOOKUP_IN_ROOT: chroot-like path resolution namei: aggressively check for nd->root escape on ".." resolution open: openat2(2) syscall selftests: add openat2(2) selftests
Documentation/filesystems/path-lookup.rst | 12 +- arch/alpha/include/uapi/asm/fcntl.h | 1 + arch/alpha/kernel/syscalls/syscall.tbl | 1 + arch/arm/tools/syscall.tbl | 1 + arch/arm64/include/asm/unistd.h | 2 +- arch/arm64/include/asm/unistd32.h | 2 + arch/ia64/kernel/syscalls/syscall.tbl | 1 + arch/m68k/kernel/syscalls/syscall.tbl | 1 + arch/microblaze/kernel/syscalls/syscall.tbl | 1 + arch/mips/kernel/syscalls/syscall_n32.tbl | 1 + arch/mips/kernel/syscalls/syscall_n64.tbl | 1 + arch/mips/kernel/syscalls/syscall_o32.tbl | 1 + arch/parisc/include/uapi/asm/fcntl.h | 39 +- arch/parisc/kernel/syscalls/syscall.tbl | 1 + arch/powerpc/kernel/syscalls/syscall.tbl | 1 + arch/s390/kernel/syscalls/syscall.tbl | 1 + arch/sh/kernel/syscalls/syscall.tbl | 1 + arch/sparc/include/uapi/asm/fcntl.h | 1 + arch/sparc/kernel/syscalls/syscall.tbl | 1 + arch/x86/entry/syscalls/syscall_32.tbl | 1 + arch/x86/entry/syscalls/syscall_64.tbl | 1 + arch/xtensa/kernel/syscalls/syscall.tbl | 1 + fs/fcntl.c | 2 +- fs/internal.h | 1 + fs/namei.c | 270 ++++++++++-- fs/open.c | 112 ++++- fs/proc/base.c | 20 +- fs/proc/fd.c | 23 +- fs/proc/namespaces.c | 2 +- include/linux/fcntl.h | 17 +- include/linux/fs.h | 8 +- include/linux/namei.h | 9 + include/linux/syscalls.h | 17 +- include/uapi/asm-generic/fcntl.h | 4 + include/uapi/asm-generic/unistd.h | 5 +- include/uapi/linux/fcntl.h | 42 ++ tools/testing/selftests/Makefile | 1 + tools/testing/selftests/memfd/memfd_test.c | 7 +- tools/testing/selftests/openat2/.gitignore | 1 + tools/testing/selftests/openat2/Makefile | 8 + tools/testing/selftests/openat2/helpers.c | 162 +++++++ tools/testing/selftests/openat2/helpers.h | 116 +++++ .../testing/selftests/openat2/linkmode_test.c | 333 +++++++++++++++ .../selftests/openat2/rename_attack_test.c | 127 ++++++ .../testing/selftests/openat2/resolve_test.c | 402 ++++++++++++++++++ 45 files changed, 1655 insertions(+), 107 deletions(-) create mode 100644 tools/testing/selftests/openat2/.gitignore create mode 100644 tools/testing/selftests/openat2/Makefile create mode 100644 tools/testing/selftests/openat2/helpers.c create mode 100644 tools/testing/selftests/openat2/helpers.h create mode 100644 tools/testing/selftests/openat2/linkmode_test.c create mode 100644 tools/testing/selftests/openat2/rename_attack_test.c create mode 100644 tools/testing/selftests/openat2/resolve_test.c
The ability for userspace to "re-open" file descriptors through /proc/self/fd has been a very useful tool for all sorts of usecases (container runtimes are one common example). However, the current interface for doing this has resulted in some pretty subtle security holes. Userspace can re-open a file descriptor with more permissions than the original, which can result in cases such as /proc/$pid/exe being re-opened O_RDWR at a later date even though (by definition) /proc/$pid/exe cannot be opened for writing. When combined with O_PATH the results can get even more confusing.
We cannot block this outright. Aside from userspace already depending on it, it's a useful feature which can actually increase the security of userspace. For instance, LXC keeps an O_PATH of the container's /dev/pts/ptmx that gets re-opened to create new ptys and then uses TIOCGPTPEER to get the slave end. This allows for pty allocation without resolving paths inside an (untrusted) container's rootfs. There isn't a trivial way of doing this that is as straight-forward and safe as O_PATH re-opening.
Instead we have to restrict it in such a way that it doesn't break (good) users but does block potential attackers. The solution applied in this patch is to restrict *re-opening* (not resolution through) magic-links by requiring that mode of the link be obeyed. Normal symlinks have modes of a+rwx but magic-links have other modes. These magic-link modes were historically ignored during path resolution, but they've now been re-purposed for more useful ends.
It is also necessary to define semantics for the mode of an O_PATH descriptor, since re-opening a magic-link through an O_PATH needs to be just as restricted as the corresponding magic-link -- otherwise the above protection can be bypassed. There are two distinct cases:
1. The target is a regular file (not a magic-link). Userspace depends on being able to re-open the O_PATH of a regular file, so we must define the mode to be a+rwx.
2. The target is a magic-link. In this case, we simply copy the mode of the magic-link. This results in an O_PATH of a magic-link effectively acting as a no-op in terms of how much re-opening privileges a process has.
CAP_DAC_OVERRIDE can be used to override all of these restrictions, but we only permit &init_userns's capabilities to affect these semantics. The reason for this is that there isn't a clear way to track what user_ns is the original owner of a given O_PATH chain -- thus an unprivileged user could create a new userns and O_PATH the file descriptor, owning it. All signs would indicate that the user really does have CAP_DAC_OVERRIDE over the new descriptor and the protection would be bypassed. We thus opt for the more conservative approach.
I have run this patch on several machines for several days. So far, the only processes which have hit this case ("loadkeys" and "kbd_mode" from the kbd package[1]) gracefully handle the permission error and do not cause any user-visible problems. In order to give users a heads-up, a warning is output to dmesg whenever may_open_magiclink() refuses access.
[1]: http://git.altlinux.org/people/legion/packages/kbd.git
Suggested-by: Andy Lutomirski luto@kernel.org Suggested-by: Christian Brauner christian@brauner.io Signed-off-by: Aleksa Sarai cyphar@cyphar.com --- Documentation/filesystems/path-lookup.rst | 12 +-- fs/internal.h | 1 + fs/namei.c | 105 +++++++++++++++++++--- fs/open.c | 3 +- fs/proc/fd.c | 23 ++++- include/linux/fs.h | 4 + include/linux/namei.h | 1 + 7 files changed, 130 insertions(+), 19 deletions(-)
diff --git a/Documentation/filesystems/path-lookup.rst b/Documentation/filesystems/path-lookup.rst index 434a07b0002b..a57d78ec8bee 100644 --- a/Documentation/filesystems/path-lookup.rst +++ b/Documentation/filesystems/path-lookup.rst @@ -1310,12 +1310,14 @@ longer needed. ``LOOKUP_JUMPED`` means that the current dentry was chosen not because it had the right name but for some other reason. This happens when following "``..``", following a symlink to ``/``, crossing a mount point -or accessing a "``/proc/$PID/fd/$FD``" symlink. In this case the -filesystem has not been asked to revalidate the name (with -``d_revalidate()``). In such cases the inode may still need to be -revalidated, so ``d_op->d_weak_revalidate()`` is called if +or accessing a "``/proc/$PID/fd/$FD``" symlink (also known as a "magic +link"). In this case the filesystem has not been asked to revalidate the +name (with ``d_revalidate()``). In such cases the inode may still need +to be revalidated, so ``d_op->d_weak_revalidate()`` is called if ``LOOKUP_JUMPED`` is set when the look completes - which may be at the -final component or, when creating, unlinking, or renaming, at the penultimate component. +final component or, when creating, unlinking, or renaming, at the +penultimate component. ``LOOKUP_MAGICLINK_JUMPED`` is set alongside +``LOOKUP_JUMPED`` if a magic-link was traversed.
Final-component flags ~~~~~~~~~~~~~~~~~~~~~ diff --git a/fs/internal.h b/fs/internal.h index 315fcd8d237c..f48449a43626 100644 --- a/fs/internal.h +++ b/fs/internal.h @@ -119,6 +119,7 @@ struct open_flags { int acc_mode; int intent; int lookup_flags; + fmode_t opath_mask; }; extern struct file *do_filp_open(int dfd, struct filename *pathname, const struct open_flags *op); diff --git a/fs/namei.c b/fs/namei.c index 209c51a5226c..54d57dad0f91 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -872,7 +872,7 @@ void nd_jump_link(struct path *path)
nd->path = *path; nd->inode = nd->path.dentry->d_inode; - nd->flags |= LOOKUP_JUMPED; + nd->flags |= LOOKUP_JUMPED | LOOKUP_MAGICLINK_JUMPED; }
static inline void put_link(struct nameidata *nd) @@ -1066,6 +1066,7 @@ const char *get_link(struct nameidata *nd) return ERR_PTR(error);
nd->last_type = LAST_BIND; + nd->flags &= ~LOOKUP_MAGICLINK_JUMPED; res = READ_ONCE(inode->i_link); if (!res) { const char * (*get)(struct dentry *, struct inode *, @@ -3501,16 +3502,73 @@ static int do_tmpfile(struct nameidata *nd, unsigned flags, return error; }
-static int do_o_path(struct nameidata *nd, unsigned flags, struct file *file) +/** + * may_reopen_magiclink - Check permissions for opening a trailing magic-link + * @upgrade_mask: the upgrade-mask of the magic-link + * @acc_mode: ACC_MODE which the user is attempting + * + * We block magic-link re-opening if the @upgrade_mask is more strict than the + * @acc_mode being requested, unless the user is capable(CAP_DAC_OVERRIDE). + * + * Returns 0 if successful, -EACCES on error. + */ +static int may_open_magiclink(fmode_t upgrade_mask, int acc_mode) { - struct path path; - int error = path_lookupat(nd, flags, &path); - if (!error) { - audit_inode(nd->name, path.dentry, 0); - error = vfs_open(&path, file); - path_put(&path); - } - return error; + /* + * We only allow for init_userns to be able to override magic-links. + * This is done to avoid cases where an unprivileged userns could take + * an O_PATH of the fd, resulting in it being very unclear whether + * CAP_DAC_OVERRIDE should work on the new O_PATH fd (given that it + * pipes through to the underlying file). + */ + if (capable(CAP_DAC_OVERRIDE)) + return 0; + + if ((acc_mode & MAY_READ) && + !(upgrade_mask & (FMODE_READ | FMODE_PATH_READ))) + goto err; + if ((acc_mode & MAY_WRITE) && + !(upgrade_mask & (FMODE_WRITE | FMODE_PATH_WRITE))) + goto err; + + return 0; + +err: + pr_warn_ratelimited("%s[%d]: magic-link re-open blocked ('%s%s%s' requested with an upgrade-mask of '%s%s%s%s')", + current->comm, task_pid_nr(current), + (acc_mode & MAY_READ) ? "r" : "", + (acc_mode & MAY_WRITE) ? "w" : "", + (acc_mode & MAY_EXEC) ? "x" : "", + (upgrade_mask & FMODE_READ) ? "r" : "", + (upgrade_mask & FMODE_PATH_READ) ? "R" : "", + (upgrade_mask & FMODE_WRITE) ? "w" : "", + (upgrade_mask & FMODE_PATH_WRITE) ? "W" : ""); + return -EACCES; +} + +static int trailing_magiclink(struct nameidata *nd, int acc_mode, + fmode_t *opath_mask) +{ + struct inode *inode = nd->link_inode; + fmode_t upgrade_mask = 0; + + /* Was the trailing_symlink() a magic-link? */ + if (!(nd->flags & LOOKUP_MAGICLINK_JUMPED)) + return 0; + + /* + * Figure out the upgrade-mask of the link_inode. Since these aren't + * strictly POSIX semantics we don't do an acl_permission_check() here, + * so we only care that at least one bit is set for each upgrade-mode. + */ + if (inode->i_mode & S_IRUGO) + upgrade_mask |= FMODE_PATH_READ; + if (inode->i_mode & S_IWUGO) + upgrade_mask |= FMODE_PATH_WRITE; + /* Restrict the O_PATH upgrade-mask of the caller. */ + if (opath_mask) + *opath_mask &= upgrade_mask; + return may_open_magiclink(upgrade_mask, acc_mode); }
static struct file *path_openat(struct nameidata *nd, @@ -3526,13 +3584,38 @@ static struct file *path_openat(struct nameidata *nd, if (unlikely(file->f_flags & __O_TMPFILE)) { error = do_tmpfile(nd, flags, op, file); } else if (unlikely(file->f_flags & O_PATH)) { - error = do_o_path(nd, flags, file); + /* Inlined path_lookupat() with a trailing_magiclink() check. */ + fmode_t opath_mask = op->opath_mask; + const char *s = path_init(nd, flags); + + while (!(error = link_path_walk(s, nd)) + && ((error = lookup_last(nd)) > 0)) { + s = trailing_symlink(nd); + error = trailing_magiclink(nd, op->acc_mode, &opath_mask); + if (error) + s = ERR_PTR(error); + } + if (!error) + error = complete_walk(nd); + + if (!error && nd->flags & LOOKUP_DIRECTORY) + if (!d_can_lookup(nd->path.dentry)) + error = -ENOTDIR; + if (!error) { + audit_inode(nd->name, nd->path.dentry, 0); + error = vfs_open(&nd->path, file); + file->f_mode |= opath_mask; + } + terminate_walk(nd); } else { const char *s = path_init(nd, flags); while (!(error = link_path_walk(s, nd)) && (error = do_last(nd, file, op)) > 0) { nd->flags &= ~(LOOKUP_OPEN|LOOKUP_CREATE|LOOKUP_EXCL); s = trailing_symlink(nd); + error = trailing_magiclink(nd, op->acc_mode, NULL); + if (error) + s = ERR_PTR(error); } terminate_walk(nd); } diff --git a/fs/open.c b/fs/open.c index a59abe3c669a..806a75d685e1 100644 --- a/fs/open.c +++ b/fs/open.c @@ -1001,8 +1001,9 @@ static inline int build_open_flags(int flags, umode_t mode, struct open_flags *o acc_mode |= MAY_APPEND;
op->acc_mode = acc_mode; - op->intent = flags & O_PATH ? 0 : LOOKUP_OPEN; + /* For O_PATH backwards-compatibility we default to an all-set mask. */ + op->opath_mask = FMODE_PATH_READ | FMODE_PATH_WRITE;
if (flags & O_CREAT) { op->intent |= LOOKUP_CREATE; diff --git a/fs/proc/fd.c b/fs/proc/fd.c index 81882a13212d..9b7d8becb002 100644 --- a/fs/proc/fd.c +++ b/fs/proc/fd.c @@ -104,11 +104,30 @@ static void tid_fd_update_inode(struct task_struct *task, struct inode *inode, task_dump_owner(task, 0, &inode->i_uid, &inode->i_gid);
if (S_ISLNK(inode->i_mode)) { + /* + * Always set +x (depending on the fmode type), since there + * currently aren't FMODE_PATH_EXEC restrictions and there is + * no O_MAYEXEC yet. This might change in the future, in which + * case we will restrict +x. + */ unsigned i_mode = S_IFLNK; + if (f_mode & FMODE_PATH) + i_mode |= S_IXGRP; + else + i_mode |= S_IXUSR; + /* + * Construct the mode bits based on the open-mode. The u+rwx + * bits are for "ordinary" open modes while g+rwx are for + * O_PATH modes. + */ if (f_mode & FMODE_READ) - i_mode |= S_IRUSR | S_IXUSR; + i_mode |= S_IRUSR; if (f_mode & FMODE_WRITE) - i_mode |= S_IWUSR | S_IXUSR; + i_mode |= S_IWUSR; + if (f_mode & FMODE_PATH_READ) + i_mode |= S_IRGRP; + if (f_mode & FMODE_PATH_WRITE) + i_mode |= S_IWGRP; inode->i_mode = i_mode; } security_task_to_inode(task, inode); diff --git a/include/linux/fs.h b/include/linux/fs.h index 997a530ff4e9..a9ad596b28e2 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -173,6 +173,10 @@ typedef int (dio_iodone_t)(struct kiocb *iocb, loff_t offset, /* File does not contribute to nr_files count */ #define FMODE_NOACCOUNT ((__force fmode_t)0x20000000)
+/* File is an O_PATH descriptor which can be upgraded to (read, write). */ +#define FMODE_PATH_READ ((__force fmode_t)0x40000000) +#define FMODE_PATH_WRITE ((__force fmode_t)0x80000000) + /* * Flag for rw_copy_check_uvector and compat_rw_copy_check_uvector * that indicates that they should check the contents of the iovec are diff --git a/include/linux/namei.h b/include/linux/namei.h index 9138b4471dbf..bd6d3eb7764d 100644 --- a/include/linux/namei.h +++ b/include/linux/namei.h @@ -49,6 +49,7 @@ enum {LAST_NORM, LAST_ROOT, LAST_DOT, LAST_DOTDOT, LAST_BIND}; #define LOOKUP_ROOT 0x2000 #define LOOKUP_EMPTY 0x4000 #define LOOKUP_DOWN 0x8000 +#define LOOKUP_MAGICLINK_JUMPED 0x10000
extern int path_pts(struct path *path);
Now that magic-link modes are obeyed for file re-opening purposes, some of the pre-existing magic-link modes need to be adjusted to be more semantically correct.
The most blatant example of this is /proc/self/exe, which had a mode of a+rwx even though tautologically the file could never be opened for writing (because it is the current->mm of a live process).
With the new O_PATH restrictions, changing the default mode of these magic-links allows us to avoid delayed-access attacks such as we saw in CVE-2019-5736.
Signed-off-by: Aleksa Sarai cyphar@cyphar.com --- fs/proc/base.c | 20 ++++++++++---------- fs/proc/namespaces.c | 2 +- 2 files changed, 11 insertions(+), 11 deletions(-)
diff --git a/fs/proc/base.c b/fs/proc/base.c index ebea9501afb8..297242174402 100644 --- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -133,9 +133,9 @@ struct pid_entry {
#define DIR(NAME, MODE, iops, fops) \ NOD(NAME, (S_IFDIR|(MODE)), &iops, &fops, {} ) -#define LNK(NAME, get_link) \ - NOD(NAME, (S_IFLNK|S_IRWXUGO), \ - &proc_pid_link_inode_operations, NULL, \ +#define LNK(NAME, MODE, get_link) \ + NOD(NAME, (S_IFLNK|(MODE)), \ + &proc_pid_link_inode_operations, NULL, \ { .proc_get_link = get_link } ) #define REG(NAME, MODE, fops) \ NOD(NAME, (S_IFREG|(MODE)), NULL, &fops, {}) @@ -3028,9 +3028,9 @@ static const struct pid_entry tgid_base_stuff[] = { REG("numa_maps", S_IRUGO, proc_pid_numa_maps_operations), #endif REG("mem", S_IRUSR|S_IWUSR, proc_mem_operations), - LNK("cwd", proc_cwd_link), - LNK("root", proc_root_link), - LNK("exe", proc_exe_link), + LNK("cwd", S_IRWXUGO, proc_cwd_link), + LNK("root", S_IRWXUGO, proc_root_link), + LNK("exe", S_IRUGO|S_IXUGO, proc_exe_link), REG("mounts", S_IRUGO, proc_mounts_operations), REG("mountinfo", S_IRUGO, proc_mountinfo_operations), REG("mountstats", S_IRUSR, proc_mountstats_operations), @@ -3429,11 +3429,11 @@ static const struct pid_entry tid_base_stuff[] = { REG("numa_maps", S_IRUGO, proc_pid_numa_maps_operations), #endif REG("mem", S_IRUSR|S_IWUSR, proc_mem_operations), - LNK("cwd", proc_cwd_link), - LNK("root", proc_root_link), - LNK("exe", proc_exe_link), + LNK("cwd", S_IRWXUGO, proc_cwd_link), + LNK("root", S_IRWXUGO, proc_root_link), + LNK("exe", S_IRUGO|S_IXUGO, proc_exe_link), REG("mounts", S_IRUGO, proc_mounts_operations), - REG("mountinfo", S_IRUGO, proc_mountinfo_operations), + REG("mountinfo", S_IRUGO, proc_mountinfo_operations), #ifdef CONFIG_PROC_PAGE_MONITOR REG("clear_refs", S_IWUSR, proc_clear_refs_operations), REG("smaps", S_IRUGO, proc_pid_smaps_operations), diff --git a/fs/proc/namespaces.c b/fs/proc/namespaces.c index dd2b35f78b09..cd1e130913f7 100644 --- a/fs/proc/namespaces.c +++ b/fs/proc/namespaces.c @@ -94,7 +94,7 @@ static struct dentry *proc_ns_instantiate(struct dentry *dentry, struct inode *inode; struct proc_inode *ei;
- inode = proc_pid_make_inode(dentry->d_sb, task, S_IFLNK | S_IRWXUGO); + inode = proc_pid_make_inode(dentry->d_sb, task, S_IFLNK | S_IRUGO); if (!inode) return ERR_PTR(-ENOENT);
Userspace has made use of /proc/self/fd very liberally to allow for descriptors to be re-opened. There are a wide variety of uses for this feature, but it has always required constructing a pathname and could not be done without procfs mounted. The obvious solution for this is to extend openat(2) to have an AT_EMPTY_PATH-equivalent -- O_EMPTYPATH.
Now that descriptor re-opening has been made safe through the new magic-link resolution restrictions, we can replicate these restrictions for O_EMPTYPATH. In particular, we only allow "upgrading" the file descriptor if the corresponding FMODE_PATH_* bit is set (or the FMODE_{READ,WRITE} cases for non-O_PATH file descriptors).
When doing openat(O_EMPTYPATH|O_PATH), O_PATH takes precedence and O_EMPTYPATH is ignored. Very few users ever have a need to O_PATH re-open an existing file descriptor, and so accommodating them at the expense of further complicating O_PATH makes little sense. Ultimately, if users ask for this we can always add RESOLVE_EMPTY_PATH to resolveat(2) in the future.
Signed-off-by: Aleksa Sarai cyphar@cyphar.com --- arch/alpha/include/uapi/asm/fcntl.h | 1 + arch/parisc/include/uapi/asm/fcntl.h | 39 ++++++++++++++-------------- arch/sparc/include/uapi/asm/fcntl.h | 1 + fs/fcntl.c | 2 +- fs/namei.c | 20 ++++++++++++++ fs/open.c | 7 ++++- include/linux/fcntl.h | 2 +- include/uapi/asm-generic/fcntl.h | 4 +++ 8 files changed, 54 insertions(+), 22 deletions(-)
diff --git a/arch/alpha/include/uapi/asm/fcntl.h b/arch/alpha/include/uapi/asm/fcntl.h index 50bdc8e8a271..1f879bade68b 100644 --- a/arch/alpha/include/uapi/asm/fcntl.h +++ b/arch/alpha/include/uapi/asm/fcntl.h @@ -34,6 +34,7 @@
#define O_PATH 040000000 #define __O_TMPFILE 0100000000 +#define O_EMPTYPATH 0200000000
#define F_GETLK 7 #define F_SETLK 8 diff --git a/arch/parisc/include/uapi/asm/fcntl.h b/arch/parisc/include/uapi/asm/fcntl.h index 03ce20e5ad7d..5d709058a76f 100644 --- a/arch/parisc/include/uapi/asm/fcntl.h +++ b/arch/parisc/include/uapi/asm/fcntl.h @@ -2,26 +2,27 @@ #ifndef _PARISC_FCNTL_H #define _PARISC_FCNTL_H
-#define O_APPEND 000000010 -#define O_BLKSEEK 000000100 /* HPUX only */ -#define O_CREAT 000000400 /* not fcntl */ -#define O_EXCL 000002000 /* not fcntl */ -#define O_LARGEFILE 000004000 -#define __O_SYNC 000100000 +#define O_APPEND 0000000010 +#define O_BLKSEEK 0000000100 /* HPUX only */ +#define O_CREAT 0000000400 /* not fcntl */ +#define O_EXCL 0000002000 /* not fcntl */ +#define O_LARGEFILE 0000004000 +#define __O_SYNC 0000100000 #define O_SYNC (__O_SYNC|O_DSYNC) -#define O_NONBLOCK 000200004 /* HPUX has separate NDELAY & NONBLOCK */ -#define O_NOCTTY 000400000 /* not fcntl */ -#define O_DSYNC 001000000 /* HPUX only */ -#define O_RSYNC 002000000 /* HPUX only */ -#define O_NOATIME 004000000 -#define O_CLOEXEC 010000000 /* set close_on_exec */ - -#define O_DIRECTORY 000010000 /* must be a directory */ -#define O_NOFOLLOW 000000200 /* don't follow links */ -#define O_INVISIBLE 004000000 /* invisible I/O, for DMAPI/XDSM */ - -#define O_PATH 020000000 -#define __O_TMPFILE 040000000 +#define O_NONBLOCK 0000200004 /* HPUX has separate NDELAY & NONBLOCK */ +#define O_NOCTTY 0000400000 /* not fcntl */ +#define O_DSYNC 0001000000 /* HPUX only */ +#define O_RSYNC 0002000000 /* HPUX only */ +#define O_NOATIME 0004000000 +#define O_CLOEXEC 0010000000 /* set close_on_exec */ + +#define O_DIRECTORY 0000010000 /* must be a directory */ +#define O_NOFOLLOW 0000000200 /* don't follow links */ +#define O_INVISIBLE 0004000000 /* invisible I/O, for DMAPI/XDSM */ + +#define O_PATH 0020000000 +#define __O_TMPFILE 0040000000 +#define O_EMPTYPATH 0100000000
#define F_GETLK64 8 #define F_SETLK64 9 diff --git a/arch/sparc/include/uapi/asm/fcntl.h b/arch/sparc/include/uapi/asm/fcntl.h index 67dae75e5274..dc86c9eaf950 100644 --- a/arch/sparc/include/uapi/asm/fcntl.h +++ b/arch/sparc/include/uapi/asm/fcntl.h @@ -37,6 +37,7 @@
#define O_PATH 0x1000000 #define __O_TMPFILE 0x2000000 +#define O_EMPTYPATH 0x4000000
#define F_GETOWN 5 /* for sockets. */ #define F_SETOWN 6 /* for sockets. */ diff --git a/fs/fcntl.c b/fs/fcntl.c index 3d40771e8e7c..4cf05a2fd162 100644 --- a/fs/fcntl.c +++ b/fs/fcntl.c @@ -1031,7 +1031,7 @@ static int __init fcntl_init(void) * Exceptions: O_NONBLOCK is a two bit define on parisc; O_NDELAY * is defined as O_NONBLOCK on some platforms and not on others. */ - BUILD_BUG_ON(21 - 1 /* for O_RDONLY being 0 */ != + BUILD_BUG_ON(22 - 1 /* for O_RDONLY being 0 */ != HWEIGHT32( (VALID_OPEN_FLAGS & ~(O_NONBLOCK | O_NDELAY)) | __FMODE_EXEC | __FMODE_NONOTIFY)); diff --git a/fs/namei.c b/fs/namei.c index 54d57dad0f91..e39b573fcc4d 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -3571,6 +3571,24 @@ static int trailing_magiclink(struct nameidata *nd, int acc_mode, return may_open_magiclink(upgrade_mask, acc_mode); }
+static int do_emptypath(struct nameidata *nd, const struct open_flags *op, + struct file *file) +{ + int error; + /* We don't support AT_FDCWD (since O_PATH is disallowed here). */ + struct fd f = fdget_raw(nd->dfd); + + if (!f.file) + return -EBADF; + + /* Apply trailing_magiclink()-like restrictions. */ + error = may_open_magiclink(f.file->f_mode, op->acc_mode); + if (!error) + error = vfs_open(&f.file->f_path, file); + fdput(f); + return error; +} + static struct file *path_openat(struct nameidata *nd, const struct open_flags *op, unsigned flags) { @@ -3583,6 +3601,8 @@ static struct file *path_openat(struct nameidata *nd,
if (unlikely(file->f_flags & __O_TMPFILE)) { error = do_tmpfile(nd, flags, op, file); + } else if (unlikely(file->f_flags & O_EMPTYPATH)) { + error = do_emptypath(nd, op, file); } else if (unlikely(file->f_flags & O_PATH)) { /* Inlined path_lookupat() with a trailing_magiclink() check. */ fmode_t opath_mask = op->opath_mask; diff --git a/fs/open.c b/fs/open.c index 806a75d685e1..310b896eecf0 100644 --- a/fs/open.c +++ b/fs/open.c @@ -1015,6 +1015,8 @@ static inline int build_open_flags(int flags, umode_t mode, struct open_flags *o lookup_flags |= LOOKUP_DIRECTORY; if (!(flags & O_NOFOLLOW)) lookup_flags |= LOOKUP_FOLLOW; + if (flags & O_EMPTYPATH) + lookup_flags |= LOOKUP_EMPTY; op->lookup_flags = lookup_flags; return 0; } @@ -1076,14 +1078,17 @@ long do_sys_open(int dfd, const char __user *filename, int flags, umode_t mode) { struct open_flags op; int fd = build_open_flags(flags, mode, &op); + int empty = 0; struct filename *tmp;
if (fd) return fd;
- tmp = getname(filename); + tmp = getname_flags(filename, op.lookup_flags, &empty); if (IS_ERR(tmp)) return PTR_ERR(tmp); + if (!empty) + op.open_flag &= ~O_EMPTYPATH;
fd = get_unused_fd_flags(flags); if (fd >= 0) { diff --git a/include/linux/fcntl.h b/include/linux/fcntl.h index d019df946cb2..2868ae6c8fc1 100644 --- a/include/linux/fcntl.h +++ b/include/linux/fcntl.h @@ -9,7 +9,7 @@ (O_RDONLY | O_WRONLY | O_RDWR | O_CREAT | O_EXCL | O_NOCTTY | O_TRUNC | \ O_APPEND | O_NDELAY | O_NONBLOCK | O_NDELAY | __O_SYNC | O_DSYNC | \ FASYNC | O_DIRECT | O_LARGEFILE | O_DIRECTORY | O_NOFOLLOW | \ - O_NOATIME | O_CLOEXEC | O_PATH | __O_TMPFILE) + O_NOATIME | O_CLOEXEC | O_PATH | __O_TMPFILE | O_EMPTYPATH)
#ifndef force_o_largefile #define force_o_largefile() (!IS_ENABLED(CONFIG_ARCH_32BIT_OFF_T)) diff --git a/include/uapi/asm-generic/fcntl.h b/include/uapi/asm-generic/fcntl.h index 9dc0bf0c5a6e..ae6862f69cc2 100644 --- a/include/uapi/asm-generic/fcntl.h +++ b/include/uapi/asm-generic/fcntl.h @@ -89,6 +89,10 @@ #define __O_TMPFILE 020000000 #endif
+#ifndef O_EMPTYPATH +#define O_EMPTYPATH 040000000 +#endif + /* a horrid kludge trying to make sure that this will fail on old kernels */ #define O_TMPFILE (__O_TMPFILE | O_DIRECTORY) #define O_TMPFILE_MASK (__O_TMPFILE | O_DIRECTORY | O_CREAT)
Add the following flags to allow various restrictions on path resolution (these affect the *entire* resolution, rather than just the final path component -- as is the case with LOOKUP_FOLLOW).
The primary justification for these flags is to allow for programs to be far more strict about how they want path resolution to handle symlinks, mountpoint crossings, and paths that escape the dirfd (through an absolute path or ".." shenanigans).
This is of particular concern to container runtimes that want to be very careful about malicious root filesystems that a container's init might have screwed around with (and there is no real way to protect against this in userspace if you consider potential races against a malicious container's init). More classical applications (which have their own potentially buggy userspace path sanitisation code) include web servers, archive extraction tools, network file servers, and so on.
These flags are exposed to userspace through openat2(2) in a later patchset.
* LOOKUP_NO_XDEV: Disallow mount-point crossing (both *down* into one, or *up* from one). Both bind-mounts and cross-filesystem mounts are blocked by this flag. The naming is based on "find -xdev" as well as -EXDEV (though find(1) doesn't walk upwards, the semantics seem obvious).
* LOOKUP_NO_MAGICLINKS: Disallows ->get_link "symlink" (or rather, magic-link) jumping. This is a very specific restriction, and it exists because /proc/$pid/fd/... "symlinks" allow for access outside nd->root and pose risk to container runtimes that don't want to be tricked into accessing a host path (but do want to allow no-funny-business symlink resolution).
* LOOKUP_NO_SYMLINKS: Disallows resolution through symlinks of any kind (including magic-links).
* LOOKUP_BENEATH: Disallow "escapes" from the starting point of the filesystem tree during resolution (you must stay "beneath" the starting point at all times). Currently this is done by disallowing ".." and absolute paths (either in the given path or found during symlink resolution) entirely, as well as all magic-link jumping.
The wholesale banning of ".." is because it is currently not safe to allow ".." resolution (races can cause the path to be moved outside of the root -- this is conceptually similar to historical chroot(2) escape attacks). Future patches in this series will address this, and will re-enable ".." resolution once it is safe. With those patches, ".." resolution will only be allowed if it remains in the root throughout resolution (such as "a/../b" not "a/../../outside/b").
The banning of magic-link jumping is done because it is not clear whether semantically they should be allowed -- while some magic-links are safe there are many that can cause escapes (and once a resolution is outside of the root, O_BENEATH will no longer detect it). Future patches may re-enable magic-link jumping when such jumps would remain inside the root.
The LOOKUP_NO_*LINK flags return -ELOOP if path resolution would violates their requirement, while the others all return -EXDEV.
This is a refresh of Al's AT_NO_JUMPS patchset[1] (which was a variation on David Drysdale's O_BENEATH patchset[2], which in turn was based on the Capsicum project[3]). Input from Linus and Andy in the AT_NO_JUMPS thread[4] determined most of the API changes made in this refresh.
[1]: https://lwn.net/Articles/721443/ [2]: https://lwn.net/Articles/619151/ [3]: https://lwn.net/Articles/603929/ [4]: https://lwn.net/Articles/723057/
Cc: Christian Brauner christian@brauner.io Suggested-by: David Drysdale drysdale@google.com Suggested-by: Al Viro viro@zeniv.linux.org.uk Suggested-by: Andy Lutomirski luto@kernel.org Suggested-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Aleksa Sarai cyphar@cyphar.com --- fs/namei.c | 85 ++++++++++++++++++++++++++++++++++++------- include/linux/namei.h | 7 ++++ 2 files changed, 78 insertions(+), 14 deletions(-)
diff --git a/fs/namei.c b/fs/namei.c index e39b573fcc4d..2e18ce5a313e 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -674,7 +674,11 @@ static int unlazy_walk(struct nameidata *nd) goto out2; if (unlikely(!legitimize_path(nd, &nd->path, nd->seq))) goto out1; - if (nd->root.mnt && !(nd->flags & LOOKUP_ROOT)) { + if (!nd->root.mnt) { + /* Restart from path_init() if nd->root was cleared. */ + if (nd->flags & LOOKUP_BENEATH) + goto out; + } else if (!(nd->flags & LOOKUP_ROOT)) { if (unlikely(!legitimize_path(nd, &nd->root, nd->root_seq))) goto out; } @@ -843,6 +847,13 @@ static inline void path_to_nameidata(const struct path *path,
static int nd_jump_root(struct nameidata *nd) { + if (unlikely(nd->flags & LOOKUP_BENEATH)) + return -EXDEV; + if (unlikely(nd->flags & LOOKUP_NO_XDEV)) { + /* Absolute path arguments to path_init() are allowed. */ + if (nd->path.mnt != NULL && nd->path.mnt != nd->root.mnt) + return -EXDEV; + } if (nd->flags & LOOKUP_RCU) { struct dentry *d; nd->path = nd->root; @@ -1051,6 +1062,9 @@ const char *get_link(struct nameidata *nd) int error; const char *res;
+ if (unlikely(nd->flags & LOOKUP_NO_SYMLINKS)) + return ERR_PTR(-ELOOP); + if (!(nd->flags & LOOKUP_RCU)) { touch_atime(&last->link); cond_resched(); @@ -1082,14 +1096,22 @@ const char *get_link(struct nameidata *nd) } else { res = get(dentry, inode, &last->done); } + if (nd->flags & LOOKUP_MAGICLINK_JUMPED) { + if (unlikely(nd->flags & LOOKUP_NO_MAGICLINKS)) + return ERR_PTR(-ELOOP); + /* Not currently safe. */ + if (unlikely(nd->flags & LOOKUP_BENEATH)) + return ERR_PTR(-EXDEV); + } if (IS_ERR_OR_NULL(res)) return res; } if (*res == '/') { if (!nd->root.mnt) set_root(nd); - if (unlikely(nd_jump_root(nd))) - return ERR_PTR(-ECHILD); + error = nd_jump_root(nd); + if (unlikely(error)) + return ERR_PTR(error); while (unlikely(*++res == '/')) ; } @@ -1270,12 +1292,16 @@ static int follow_managed(struct path *path, struct nameidata *nd) break; }
- if (need_mntput && path->mnt == mnt) - mntput(path->mnt); + if (need_mntput) { + if (path->mnt == mnt) + mntput(path->mnt); + if (unlikely(nd->flags & LOOKUP_NO_XDEV)) + ret = -EXDEV; + else + nd->flags |= LOOKUP_JUMPED; + } if (ret == -EISDIR || !ret) ret = 1; - if (need_mntput) - nd->flags |= LOOKUP_JUMPED; if (unlikely(ret < 0)) path_put_conditional(path, nd); return ret; @@ -1332,6 +1358,8 @@ static bool __follow_mount_rcu(struct nameidata *nd, struct path *path, mounted = __lookup_mnt(path->mnt, path->dentry); if (!mounted) break; + if (unlikely(nd->flags & LOOKUP_NO_XDEV)) + return false; path->mnt = &mounted->mnt; path->dentry = mounted->mnt.mnt_root; nd->flags |= LOOKUP_JUMPED; @@ -1352,8 +1380,11 @@ static int follow_dotdot_rcu(struct nameidata *nd) struct inode *inode = nd->inode;
while (1) { - if (path_equal(&nd->path, &nd->root)) + if (path_equal(&nd->path, &nd->root)) { + if (unlikely(nd->flags & LOOKUP_BENEATH)) + return -EXDEV; break; + } if (nd->path.dentry != nd->path.mnt->mnt_root) { struct dentry *old = nd->path.dentry; struct dentry *parent = old->d_parent; @@ -1378,6 +1409,8 @@ static int follow_dotdot_rcu(struct nameidata *nd) return -ECHILD; if (&mparent->mnt == nd->path.mnt) break; + if (unlikely(nd->flags & LOOKUP_NO_XDEV)) + return -EXDEV; /* we know that mountpoint was pinned */ nd->path.dentry = mountpoint; nd->path.mnt = &mparent->mnt; @@ -1392,6 +1425,8 @@ static int follow_dotdot_rcu(struct nameidata *nd) return -ECHILD; if (!mounted) break; + if (unlikely(nd->flags & LOOKUP_NO_XDEV)) + return -EXDEV; nd->path.mnt = &mounted->mnt; nd->path.dentry = mounted->mnt.mnt_root; inode = nd->path.dentry->d_inode; @@ -1480,8 +1515,11 @@ static int path_parent_directory(struct path *path) static int follow_dotdot(struct nameidata *nd) { while(1) { - if (path_equal(&nd->path, &nd->root)) + if (path_equal(&nd->path, &nd->root)) { + if (unlikely(nd->flags & LOOKUP_BENEATH)) + return -EXDEV; break; + } if (nd->path.dentry != nd->path.mnt->mnt_root) { int ret = path_parent_directory(&nd->path); if (ret) @@ -1490,6 +1528,8 @@ static int follow_dotdot(struct nameidata *nd) } if (!follow_up(&nd->path)) break; + if (unlikely(nd->flags & LOOKUP_NO_XDEV)) + return -EXDEV; } follow_mount(&nd->path); nd->inode = nd->path.dentry->d_inode; @@ -1704,6 +1744,13 @@ static inline int may_lookup(struct nameidata *nd) static inline int handle_dots(struct nameidata *nd, int type) { if (type == LAST_DOTDOT) { + /* + * LOOKUP_BENEATH resolving ".." is not currently safe -- races + * can cause our parent to have moved outside of the root and + * us to skip over it. + */ + if (unlikely(nd->flags & LOOKUP_BENEATH)) + return -EXDEV; if (!nd->root.mnt) set_root(nd); if (nd->flags & LOOKUP_RCU) { @@ -2170,6 +2217,7 @@ static int link_path_walk(const char *name, struct nameidata *nd) /* must be paired with terminate_walk() */ static const char *path_init(struct nameidata *nd, unsigned flags) { + int error; const char *s = nd->name->name;
if (!*s) @@ -2202,11 +2250,13 @@ static const char *path_init(struct nameidata *nd, unsigned flags) nd->path.dentry = NULL;
nd->m_seq = read_seqbegin(&mount_lock); + + /* Figure out the starting path and root (if needed). */ if (*s == '/') { set_root(nd); - if (likely(!nd_jump_root(nd))) - return s; - return ERR_PTR(-ECHILD); + error = nd_jump_root(nd); + if (unlikely(error)) + return ERR_PTR(error); } else if (nd->dfd == AT_FDCWD) { if (flags & LOOKUP_RCU) { struct fs_struct *fs = current->fs; @@ -2222,7 +2272,6 @@ static const char *path_init(struct nameidata *nd, unsigned flags) get_fs_pwd(current->fs, &nd->path); nd->inode = nd->path.dentry->d_inode; } - return s; } else { /* Caller must check execute permissions on the starting path component */ struct fd f = fdget_raw(nd->dfd); @@ -2247,8 +2296,16 @@ static const char *path_init(struct nameidata *nd, unsigned flags) nd->inode = nd->path.dentry->d_inode; } fdput(f); - return s; } + /* For scoped-lookups we need to set the root to the dirfd as well. */ + if (flags & LOOKUP_BENEATH) { + nd->root = nd->path; + if (flags & LOOKUP_RCU) + nd->root_seq = nd->seq; + else + path_get(&nd->root); + } + return s; }
static const char *trailing_symlink(struct nameidata *nd) diff --git a/include/linux/namei.h b/include/linux/namei.h index bd6d3eb7764d..be407415c28a 100644 --- a/include/linux/namei.h +++ b/include/linux/namei.h @@ -51,6 +51,13 @@ enum {LAST_NORM, LAST_ROOT, LAST_DOT, LAST_DOTDOT, LAST_BIND}; #define LOOKUP_DOWN 0x8000 #define LOOKUP_MAGICLINK_JUMPED 0x10000
+/* Scoping flags for lookup. */ +#define LOOKUP_BENEATH 0x020000 /* No escaping from starting point. */ +#define LOOKUP_NO_XDEV 0x040000 /* No mountpoint crossing. */ +#define LOOKUP_NO_MAGICLINKS 0x080000 /* No /proc/$pid/fd/ "symlink" crossing. */ +#define LOOKUP_NO_SYMLINKS 0x100000 /* No symlink crossing *at all*. + Implies LOOKUP_NO_MAGICLINKS. */ + extern int path_pts(struct path *path);
extern int user_path_at_empty(int, const char __user *, unsigned, struct path *, int *empty);
The primary motivation for the need for this flag is container runtimes which have to interact with malicious root filesystems in the host namespaces. One of the first requirements for a container runtime to be secure against a malicious rootfs is that they correctly scope symlinks (that is, they should be scoped as though they are chroot(2)ed into the container's rootfs) and ".."-style paths[*]. The already-existing LOOKUP_NO_XDEV and LOOKUP_NO_MAGICLINKS help defend against other potential attacks in a malicious rootfs scenario.
Currently most container runtimes try to do this resolution in userspace[1], causing many potential race conditions. In addition, the "obvious" alternative (actually performing a {ch,pivot_}root(2)) requires a fork+exec (for some runtimes) which is *very* costly if necessary for every filesystem operation involving a container.
[*] At the moment, ".." and magic-link jumping are disallowed for the same reason it is disabled for LOOKUP_BENEATH -- currently it is not safe to allow it. Future patches may enable it unconditionally once we have resolved the possible races (for "..") and semantics (for magic-link jumping).
The most significant *at(2) semantic change with LOOKUP_IN_ROOT is that absolute pathnames no longer cause the dirfd to be ignored completely.
The rationale is that LOOKUP_IN_ROOT must necessarily chroot-scope symlinks with absolute paths to dirfd, and so doing it for the base path seems to be the most consistent behaviour (and also avoids foot-gunning users who want to scope paths that are absolute).
[1]: https://github.com/cyphar/filepath-securejoin
Suggested-by: Christian Brauner christian@brauner.io Signed-off-by: Aleksa Sarai cyphar@cyphar.com --- fs/namei.c | 41 +++++++++++++++++++++++++++++++---------- include/linux/namei.h | 1 + 2 files changed, 32 insertions(+), 10 deletions(-)
diff --git a/fs/namei.c b/fs/namei.c index 2e18ce5a313e..0352d275bd13 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -676,7 +676,7 @@ static int unlazy_walk(struct nameidata *nd) goto out1; if (!nd->root.mnt) { /* Restart from path_init() if nd->root was cleared. */ - if (nd->flags & LOOKUP_BENEATH) + if (nd->flags & (LOOKUP_BENEATH | LOOKUP_IN_ROOT)) goto out; } else if (!(nd->flags & LOOKUP_ROOT)) { if (unlikely(!legitimize_path(nd, &nd->root, nd->root_seq))) @@ -809,10 +809,18 @@ static int complete_walk(struct nameidata *nd) return status; }
-static void set_root(struct nameidata *nd) +static int set_root(struct nameidata *nd) { struct fs_struct *fs = current->fs;
+ /* + * Jumping to the real root as part of LOOKUP_IN_ROOT is a BUG in namei, + * but we still have to ensure it doesn't happen because it will cause a + * breakout from the dirfd. + */ + if (WARN_ON(nd->flags & LOOKUP_IN_ROOT)) + return -ENOTRECOVERABLE; + if (nd->flags & LOOKUP_RCU) { unsigned seq;
@@ -824,6 +832,7 @@ static void set_root(struct nameidata *nd) } else { get_fs_root(fs, &nd->root); } + return 0; }
static void path_put_conditional(struct path *path, struct nameidata *nd) @@ -854,6 +863,11 @@ static int nd_jump_root(struct nameidata *nd) if (nd->path.mnt != NULL && nd->path.mnt != nd->root.mnt) return -EXDEV; } + if (!nd->root.mnt) { + int error = set_root(nd); + if (error) + return error; + } if (nd->flags & LOOKUP_RCU) { struct dentry *d; nd->path = nd->root; @@ -1100,15 +1114,13 @@ const char *get_link(struct nameidata *nd) if (unlikely(nd->flags & LOOKUP_NO_MAGICLINKS)) return ERR_PTR(-ELOOP); /* Not currently safe. */ - if (unlikely(nd->flags & LOOKUP_BENEATH)) + if (unlikely(nd->flags & (LOOKUP_BENEATH | LOOKUP_IN_ROOT))) return ERR_PTR(-EXDEV); } if (IS_ERR_OR_NULL(res)) return res; } if (*res == '/') { - if (!nd->root.mnt) - set_root(nd); error = nd_jump_root(nd); if (unlikely(error)) return ERR_PTR(error); @@ -1744,15 +1756,20 @@ static inline int may_lookup(struct nameidata *nd) static inline int handle_dots(struct nameidata *nd, int type) { if (type == LAST_DOTDOT) { + int error = 0; + /* * LOOKUP_BENEATH resolving ".." is not currently safe -- races * can cause our parent to have moved outside of the root and * us to skip over it. */ - if (unlikely(nd->flags & LOOKUP_BENEATH)) + if (unlikely(nd->flags & (LOOKUP_BENEATH | LOOKUP_IN_ROOT))) return -EXDEV; - if (!nd->root.mnt) - set_root(nd); + if (!nd->root.mnt) { + error = set_root(nd); + if (error) + return error; + } if (nd->flags & LOOKUP_RCU) { return follow_dotdot_rcu(nd); } else @@ -2251,9 +2268,13 @@ static const char *path_init(struct nameidata *nd, unsigned flags)
nd->m_seq = read_seqbegin(&mount_lock);
+ /* LOOKUP_IN_ROOT treats absolute paths as being relative-to-dirfd. */ + if (flags & LOOKUP_IN_ROOT) + while (*s == '/') + s++; + /* Figure out the starting path and root (if needed). */ if (*s == '/') { - set_root(nd); error = nd_jump_root(nd); if (unlikely(error)) return ERR_PTR(error); @@ -2298,7 +2319,7 @@ static const char *path_init(struct nameidata *nd, unsigned flags) fdput(f); } /* For scoped-lookups we need to set the root to the dirfd as well. */ - if (flags & LOOKUP_BENEATH) { + if (flags & (LOOKUP_BENEATH | LOOKUP_IN_ROOT)) { nd->root = nd->path; if (flags & LOOKUP_RCU) nd->root_seq = nd->seq; diff --git a/include/linux/namei.h b/include/linux/namei.h index be407415c28a..ec2c6c588ea7 100644 --- a/include/linux/namei.h +++ b/include/linux/namei.h @@ -57,6 +57,7 @@ enum {LAST_NORM, LAST_ROOT, LAST_DOT, LAST_DOTDOT, LAST_BIND}; #define LOOKUP_NO_MAGICLINKS 0x080000 /* No /proc/$pid/fd/ "symlink" crossing. */ #define LOOKUP_NO_SYMLINKS 0x100000 /* No symlink crossing *at all*. Implies LOOKUP_NO_MAGICLINKS. */ +#define LOOKUP_IN_ROOT 0x200000 /* Treat dirfd as %current->fs->root. */
extern int path_pts(struct path *path);
This patch allows for LOOKUP_BENEATH and LOOKUP_IN_ROOT to safely permit ".." resolution (in the case of LOOKUP_BENEATH the resolution will still fail if ".." resolution would resolve a path outside of the root -- while LOOKUP_IN_ROOT will chroot(2)-style scope it). Magic-link jumps are still disallowed entirely because now they could result in inconsistent behaviour if resolution encounters a subsequent ".."[*].
The need for this patch is explained by observing there is a fairly easy-to-exploit race condition with chroot(2) (and thus by extension LOOKUP_IN_ROOT and LOOKUP_BENEATH if ".." is allowed) where a rename(2) of a path can be used to "skip over" nd->root and thus escape to the filesystem above nd->root.
thread1 [attacker]: for (;;) renameat2(AT_FDCWD, "/a/b/c", AT_FDCWD, "/a/d", RENAME_EXCHANGE); thread2 [victim]: for (;;) openat2(dirb, "b/c/../../etc/shadow", { .flags = O_PATH, .resolve = RESOLVE_IN_ROOT } );
With fairly significant regularity, thread2 will resolve to "/etc/shadow" rather than "/a/b/etc/shadow". There is also a similar (though somewhat more privileged) attack using MS_MOVE.
With this patch, such cases will be detected *during* ".." resolution (which is the weak point of chroot(2) -- since walking *into* a subdirectory tautologically cannot result in you walking *outside* nd->root -- except through a bind-mount or magic-link). By detecting this at ".." resolution (rather than checking only at the end of the entire resolution) we can both correct escapes by jumping back to the root (in the case of LOOKUP_IN_ROOT), as well as avoid revealing to attackers the structure of the filesystem outside of the root (through timing attacks for instance).
In order to avoid a quadratic lookup with each ".." entry, we only activate the slow path if a write through &rename_lock or &mount_lock has occurred during path resolution (&rename_lock and &mount_lock are re-taken to further optimise the lookup). Since the primary attack being protected against is MS_MOVE or rename(2), not doing additional checks unless a mount or rename have occurred avoids making the common case slow.
The use of path_is_under() here might seem suspect, but on further inspection of the most important race (a path was *inside* the root but is now *outside*), there appears to be no attack potential:
* If path_is_under() occurs before the rename, then the path will be resolved -- however the path was originally inside the root and thus there is no escape (and to userspace it'd look like the rename occurred after the path was resolved). If path_is_under() occurs afterwards, the resolution is blocked.
* Subsequent ".." jumps are guaranteed to check path_is_under() -- by construction, &rename_lock or &mount_lock must have been taken by the attacker after path_is_under() returned in the victim. Thus ".." will not be able to escape from the previously-inside-root path.
* Walking down in the moved path is still safe since the entire subtree was moved (either by rename(2) or MS_MOVE) and because (as discussed above) walking down is safe.
A variant of the above attack is included in the selftests for openat2(2) later in this patch series. I've run this test on several machines for several days and no instances of a breakout were detected. While this is not concrete proof that this is safe, when combined with the above argument it should lend some trustworthiness to this construction.
[*] It may be acceptable in the future to do a path_is_under() check after resolving a magic-link and permit resolution if the nd_jump_link() result is still within the dirfd. However this seems unlikely to be a feature that people *really* need* -- it can be added later if it turns out a lot of people want it.
Cc: Al Viro viro@zeniv.linux.org.uk Cc: Jann Horn jannh@google.com Cc: Kees Cook keescook@chromium.org Signed-off-by: Aleksa Sarai cyphar@cyphar.com --- fs/namei.c | 45 +++++++++++++++++++++++++++++++-------------- 1 file changed, 31 insertions(+), 14 deletions(-)
diff --git a/fs/namei.c b/fs/namei.c index 0352d275bd13..fd1eb5ce8baa 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -491,7 +491,7 @@ struct nameidata { struct path root; struct inode *inode; /* path.dentry.d_inode */ unsigned int flags; - unsigned seq, m_seq; + unsigned seq, m_seq, r_seq; int last_type; unsigned depth; int total_link_count; @@ -1758,22 +1758,36 @@ static inline int handle_dots(struct nameidata *nd, int type) if (type == LAST_DOTDOT) { int error = 0;
- /* - * LOOKUP_BENEATH resolving ".." is not currently safe -- races - * can cause our parent to have moved outside of the root and - * us to skip over it. - */ - if (unlikely(nd->flags & (LOOKUP_BENEATH | LOOKUP_IN_ROOT))) - return -EXDEV; if (!nd->root.mnt) { error = set_root(nd); if (error) return error; } - if (nd->flags & LOOKUP_RCU) { - return follow_dotdot_rcu(nd); - } else - return follow_dotdot(nd); + if (nd->flags & LOOKUP_RCU) + error = follow_dotdot_rcu(nd); + else + error = follow_dotdot(nd); + if (error) + return error; + + if (unlikely(nd->flags & (LOOKUP_BENEATH | LOOKUP_IN_ROOT))) { + bool m_retry = read_seqretry(&mount_lock, nd->m_seq); + bool r_retry = read_seqretry(&rename_lock, nd->r_seq); + + /* + * Don't bother checking unless there's a racing + * rename(2) or MS_MOVE. + */ + if (likely(!m_retry && !r_retry)) + return 0; + + if (m_retry && !(nd->flags & LOOKUP_RCU)) + nd->m_seq = read_seqbegin(&mount_lock); + if (r_retry) + nd->r_seq = read_seqbegin(&rename_lock); + if (!path_is_under(&nd->path, &nd->root)) + return -EXDEV; + } } return 0; } @@ -2245,6 +2259,11 @@ static const char *path_init(struct nameidata *nd, unsigned flags) nd->last_type = LAST_ROOT; /* if there are only slashes... */ nd->flags = flags | LOOKUP_JUMPED | LOOKUP_PARENT; nd->depth = 0; + + nd->m_seq = read_seqbegin(&mount_lock); + if (flags & (LOOKUP_BENEATH | LOOKUP_IN_ROOT)) + nd->r_seq = read_seqbegin(&rename_lock); + if (flags & LOOKUP_ROOT) { struct dentry *root = nd->root.dentry; struct inode *inode = root->d_inode; @@ -2266,8 +2285,6 @@ static const char *path_init(struct nameidata *nd, unsigned flags) nd->path.mnt = NULL; nd->path.dentry = NULL;
- nd->m_seq = read_seqbegin(&mount_lock); - /* LOOKUP_IN_ROOT treats absolute paths as being relative-to-dirfd. */ if (flags & LOOKUP_IN_ROOT) while (*s == '/')
The most obvious syscall to add support for the new LOOKUP_* scoping flags would be openat(2). However, there are a few reasons why this is not the best course of action:
* The new LOOKUP_* flags are intended to be security features, and openat(2) will silently ignore all unknown flags. This means that users would need to avoid foot-gunning themselves constantly when using this interface if it were part of openat(2). This can be fixed by having userspace libraries handle this for users[1], but should be avoided if possible.
* Resolution scoping feels like a different operation to the existing O_* flags. And since openat(2) has limited flag space, it seems to be quite wasteful to clutter it with 5 flags that are all resolution-related. Arguably O_NOFOLLOW is also a resolution flag but its entire purpose is to error out if you encounter a trailing symlink -- not to scope resolution.
* Other systems would be able to reimplement this syscall allowing for cross-OS standardisation rather than being hidden amongst O_* flags which may result in it not being used by all the parties that might want to use it (file servers, web servers, container runtimes, etc).
* It gives us the opportunity to iterate on the O_PATH interface. In particular, the new @how->upgrade_mask field for fd re-opening is only possible because we have a clean slate without needing to re-use the ACC_MODE flag design nor the existing openat(2) @mode semantics.
To this end, we introduce the openat2(2) syscall. It provides all of the features of openat(2) through the @how->flags argument, but also also provides a new @how->resolve argument which exposes RESOLVE_* flags that map to our new LOOKUP_* flags. It also eliminates the long-standing ugliness of variadic-open(2) by embedding it in a struct.
In order to allow for userspace to lock down their usage of file descriptor re-opening, openat2(2) has the ability for users to disallow certain re-opening modes through @how->upgrade_mask. At the moment, there is no UPGRADE_NOEXEC. The open_how struct is padded to 64 bytes for future extensions (all of the reserved bits must be zeroed).
[1]: https://github.com/openSUSE/libpathrs
Suggested-by: Christian Brauner christian@brauner.io Signed-off-by: Aleksa Sarai cyphar@cyphar.com --- arch/alpha/kernel/syscalls/syscall.tbl | 1 + arch/arm/tools/syscall.tbl | 1 + arch/arm64/include/asm/unistd.h | 2 +- arch/arm64/include/asm/unistd32.h | 2 + arch/ia64/kernel/syscalls/syscall.tbl | 1 + arch/m68k/kernel/syscalls/syscall.tbl | 1 + arch/microblaze/kernel/syscalls/syscall.tbl | 1 + arch/mips/kernel/syscalls/syscall_n32.tbl | 1 + arch/mips/kernel/syscalls/syscall_n64.tbl | 1 + arch/mips/kernel/syscalls/syscall_o32.tbl | 1 + arch/parisc/kernel/syscalls/syscall.tbl | 1 + arch/powerpc/kernel/syscalls/syscall.tbl | 1 + arch/s390/kernel/syscalls/syscall.tbl | 1 + arch/sh/kernel/syscalls/syscall.tbl | 1 + arch/sparc/kernel/syscalls/syscall.tbl | 1 + arch/x86/entry/syscalls/syscall_32.tbl | 1 + arch/x86/entry/syscalls/syscall_64.tbl | 1 + arch/xtensa/kernel/syscalls/syscall.tbl | 1 + fs/open.c | 106 ++++++++++++++++---- include/linux/fcntl.h | 15 ++- include/linux/fs.h | 4 +- include/linux/syscalls.h | 17 +++- include/uapi/asm-generic/unistd.h | 5 +- include/uapi/linux/fcntl.h | 42 ++++++++ 24 files changed, 179 insertions(+), 30 deletions(-)
diff --git a/arch/alpha/kernel/syscalls/syscall.tbl b/arch/alpha/kernel/syscalls/syscall.tbl index 728fe028c02c..9f374f7d9514 100644 --- a/arch/alpha/kernel/syscalls/syscall.tbl +++ b/arch/alpha/kernel/syscalls/syscall.tbl @@ -475,3 +475,4 @@ 543 common fspick sys_fspick 544 common pidfd_open sys_pidfd_open # 545 reserved for clone3 +547 common openat2 sys_openat2 diff --git a/arch/arm/tools/syscall.tbl b/arch/arm/tools/syscall.tbl index 6da7dc4d79cc..4ba54bc7e19a 100644 --- a/arch/arm/tools/syscall.tbl +++ b/arch/arm/tools/syscall.tbl @@ -449,3 +449,4 @@ 433 common fspick sys_fspick 434 common pidfd_open sys_pidfd_open 435 common clone3 sys_clone3 +437 common openat2 sys_openat2 diff --git a/arch/arm64/include/asm/unistd.h b/arch/arm64/include/asm/unistd.h index 2629a68b8724..8aa00ccb0b96 100644 --- a/arch/arm64/include/asm/unistd.h +++ b/arch/arm64/include/asm/unistd.h @@ -38,7 +38,7 @@ #define __ARM_NR_compat_set_tls (__ARM_NR_COMPAT_BASE + 5) #define __ARM_NR_COMPAT_END (__ARM_NR_COMPAT_BASE + 0x800)
-#define __NR_compat_syscalls 436 +#define __NR_compat_syscalls 438 #endif
#define __ARCH_WANT_SYS_CLONE diff --git a/arch/arm64/include/asm/unistd32.h b/arch/arm64/include/asm/unistd32.h index 94ab29cf4f00..57f6f592d460 100644 --- a/arch/arm64/include/asm/unistd32.h +++ b/arch/arm64/include/asm/unistd32.h @@ -879,6 +879,8 @@ __SYSCALL(__NR_fspick, sys_fspick) __SYSCALL(__NR_pidfd_open, sys_pidfd_open) #define __NR_clone3 435 __SYSCALL(__NR_clone3, sys_clone3) +#define __NR_openat2 437 +__SYSCALL(__NR_openat2, sys_openat2)
/* * Please add new compat syscalls above this comment and update diff --git a/arch/ia64/kernel/syscalls/syscall.tbl b/arch/ia64/kernel/syscalls/syscall.tbl index 36d5faf4c86c..8d36f2e2dc89 100644 --- a/arch/ia64/kernel/syscalls/syscall.tbl +++ b/arch/ia64/kernel/syscalls/syscall.tbl @@ -356,3 +356,4 @@ 433 common fspick sys_fspick 434 common pidfd_open sys_pidfd_open # 435 reserved for clone3 +437 common openat2 sys_openat2 diff --git a/arch/m68k/kernel/syscalls/syscall.tbl b/arch/m68k/kernel/syscalls/syscall.tbl index a88a285a0e5f..2559925f1924 100644 --- a/arch/m68k/kernel/syscalls/syscall.tbl +++ b/arch/m68k/kernel/syscalls/syscall.tbl @@ -435,3 +435,4 @@ 433 common fspick sys_fspick 434 common pidfd_open sys_pidfd_open # 435 reserved for clone3 +437 common openat2 sys_openat2 diff --git a/arch/microblaze/kernel/syscalls/syscall.tbl b/arch/microblaze/kernel/syscalls/syscall.tbl index 09b0cd7dab0a..c04385e60833 100644 --- a/arch/microblaze/kernel/syscalls/syscall.tbl +++ b/arch/microblaze/kernel/syscalls/syscall.tbl @@ -441,3 +441,4 @@ 433 common fspick sys_fspick 434 common pidfd_open sys_pidfd_open 435 common clone3 sys_clone3 +437 common openat2 sys_openat2 diff --git a/arch/mips/kernel/syscalls/syscall_n32.tbl b/arch/mips/kernel/syscalls/syscall_n32.tbl index c9c879ec9b6d..ba06cae655c6 100644 --- a/arch/mips/kernel/syscalls/syscall_n32.tbl +++ b/arch/mips/kernel/syscalls/syscall_n32.tbl @@ -374,3 +374,4 @@ 433 n32 fspick sys_fspick 434 n32 pidfd_open sys_pidfd_open # 435 reserved for clone3 +437 n32 openat2 sys_openat2 diff --git a/arch/mips/kernel/syscalls/syscall_n64.tbl b/arch/mips/kernel/syscalls/syscall_n64.tbl index bbce9159caa1..0f3de320ae51 100644 --- a/arch/mips/kernel/syscalls/syscall_n64.tbl +++ b/arch/mips/kernel/syscalls/syscall_n64.tbl @@ -350,3 +350,4 @@ 433 n64 fspick sys_fspick 434 n64 pidfd_open sys_pidfd_open # 435 reserved for clone3 +437 n64 openat2 sys_openat2 diff --git a/arch/mips/kernel/syscalls/syscall_o32.tbl b/arch/mips/kernel/syscalls/syscall_o32.tbl index 9653591428ec..f108464d09a3 100644 --- a/arch/mips/kernel/syscalls/syscall_o32.tbl +++ b/arch/mips/kernel/syscalls/syscall_o32.tbl @@ -423,3 +423,4 @@ 433 o32 fspick sys_fspick 434 o32 pidfd_open sys_pidfd_open # 435 reserved for clone3 +437 o32 openat2 sys_openat2 sys_openat2 diff --git a/arch/parisc/kernel/syscalls/syscall.tbl b/arch/parisc/kernel/syscalls/syscall.tbl index 670d1371aca1..45ddc4485844 100644 --- a/arch/parisc/kernel/syscalls/syscall.tbl +++ b/arch/parisc/kernel/syscalls/syscall.tbl @@ -432,3 +432,4 @@ 433 common fspick sys_fspick 434 common pidfd_open sys_pidfd_open 435 common clone3 sys_clone3_wrapper +437 common openat2 sys_openat2 diff --git a/arch/powerpc/kernel/syscalls/syscall.tbl b/arch/powerpc/kernel/syscalls/syscall.tbl index 43f736ed47f2..a8b5ecb5b602 100644 --- a/arch/powerpc/kernel/syscalls/syscall.tbl +++ b/arch/powerpc/kernel/syscalls/syscall.tbl @@ -517,3 +517,4 @@ 433 common fspick sys_fspick 434 common pidfd_open sys_pidfd_open 435 nospu clone3 ppc_clone3 +437 common openat2 sys_openat2 diff --git a/arch/s390/kernel/syscalls/syscall.tbl b/arch/s390/kernel/syscalls/syscall.tbl index 3054e9c035a3..16b571c06161 100644 --- a/arch/s390/kernel/syscalls/syscall.tbl +++ b/arch/s390/kernel/syscalls/syscall.tbl @@ -438,3 +438,4 @@ 433 common fspick sys_fspick sys_fspick 434 common pidfd_open sys_pidfd_open sys_pidfd_open 435 common clone3 sys_clone3 sys_clone3 +437 common openat2 sys_openat2 sys_openat2 diff --git a/arch/sh/kernel/syscalls/syscall.tbl b/arch/sh/kernel/syscalls/syscall.tbl index b5ed26c4c005..a7185cc18626 100644 --- a/arch/sh/kernel/syscalls/syscall.tbl +++ b/arch/sh/kernel/syscalls/syscall.tbl @@ -438,3 +438,4 @@ 433 common fspick sys_fspick 434 common pidfd_open sys_pidfd_open # 435 reserved for clone3 +437 common openat2 sys_openat2 diff --git a/arch/sparc/kernel/syscalls/syscall.tbl b/arch/sparc/kernel/syscalls/syscall.tbl index 8c8cc7537fb2..b11c19552022 100644 --- a/arch/sparc/kernel/syscalls/syscall.tbl +++ b/arch/sparc/kernel/syscalls/syscall.tbl @@ -481,3 +481,4 @@ 433 common fspick sys_fspick 434 common pidfd_open sys_pidfd_open # 435 reserved for clone3 +437 common openat2 sys_openat2 diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl index c00019abd076..dfa1dc5c8587 100644 --- a/arch/x86/entry/syscalls/syscall_32.tbl +++ b/arch/x86/entry/syscalls/syscall_32.tbl @@ -440,3 +440,4 @@ 433 i386 fspick sys_fspick __ia32_sys_fspick 434 i386 pidfd_open sys_pidfd_open __ia32_sys_pidfd_open 435 i386 clone3 sys_clone3 __ia32_sys_clone3 +437 i386 openat2 sys_openat2 __ia32_sys_openat2 diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl index c29976eca4a8..9035647ef236 100644 --- a/arch/x86/entry/syscalls/syscall_64.tbl +++ b/arch/x86/entry/syscalls/syscall_64.tbl @@ -357,6 +357,7 @@ 433 common fspick __x64_sys_fspick 434 common pidfd_open __x64_sys_pidfd_open 435 common clone3 __x64_sys_clone3/ptregs +437 common openat2 __x64_sys_openat2
# # x32-specific system call numbers start at 512 to avoid cache impact diff --git a/arch/xtensa/kernel/syscalls/syscall.tbl b/arch/xtensa/kernel/syscalls/syscall.tbl index 25f4de729a6d..f0a68013c038 100644 --- a/arch/xtensa/kernel/syscalls/syscall.tbl +++ b/arch/xtensa/kernel/syscalls/syscall.tbl @@ -406,3 +406,4 @@ 433 common fspick sys_fspick 434 common pidfd_open sys_pidfd_open 435 common clone3 sys_clone3 +437 common openat2 sys_openat2 diff --git a/fs/open.c b/fs/open.c index 310b896eecf0..0f050b5e6921 100644 --- a/fs/open.c +++ b/fs/open.c @@ -947,19 +947,29 @@ struct file *open_with_fake_path(const struct path *path, int flags, } EXPORT_SYMBOL(open_with_fake_path);
-static inline int build_open_flags(int flags, umode_t mode, struct open_flags *op) +static inline int build_open_flags(const struct open_how *how, + struct open_flags *op) { + int flags = how->flags; int lookup_flags = 0; + int opath_mask = 0; int acc_mode = ACC_MODE(flags);
/* - * Clear out all open flags we don't know about so that we don't report - * them in fcntl(F_GETFD) or similar interfaces. + * Older syscalls still clear these bits before calling + * build_open_flags(), but openat2(2) checks all its arguments. */ - flags &= VALID_OPEN_FLAGS; + if (flags & ~VALID_OPEN_FLAGS) + return -EINVAL; + if (how->resolve & ~VALID_RESOLVE_FLAGS) + return -EINVAL; + if (!(how->flags & (O_PATH | O_CREAT | __O_TMPFILE)) && how->mode != 0) + return -EINVAL; + if (memchr_inv(how->reserved, 0, sizeof(how->reserved))) + return -EINVAL;
if (flags & (O_CREAT | __O_TMPFILE)) - op->mode = (mode & S_IALLUGO) | S_IFREG; + op->mode = (how->mode & S_IALLUGO) | S_IFREG; else op->mode = 0;
@@ -987,6 +997,14 @@ static inline int build_open_flags(int flags, umode_t mode, struct open_flags *o */ flags &= O_DIRECTORY | O_NOFOLLOW | O_PATH; acc_mode = 0; + + /* Allow userspace to restrict the re-opening of O_PATH fds. */ + if (how->upgrade_mask & ~VALID_UPGRADE_FLAGS) + return -EINVAL; + if (!(how->upgrade_mask & UPGRADE_NOREAD)) + opath_mask |= FMODE_PATH_READ; + if (!(how->upgrade_mask & UPGRADE_NOWRITE)) + opath_mask |= FMODE_PATH_WRITE; }
op->open_flag = flags; @@ -1002,8 +1020,7 @@ static inline int build_open_flags(int flags, umode_t mode, struct open_flags *o
op->acc_mode = acc_mode; op->intent = flags & O_PATH ? 0 : LOOKUP_OPEN; - /* For O_PATH backwards-compatibility we default to an all-set mask. */ - op->opath_mask = FMODE_PATH_READ | FMODE_PATH_WRITE; + op->opath_mask = opath_mask;
if (flags & O_CREAT) { op->intent |= LOOKUP_CREATE; @@ -1017,6 +1034,18 @@ static inline int build_open_flags(int flags, umode_t mode, struct open_flags *o lookup_flags |= LOOKUP_FOLLOW; if (flags & O_EMPTYPATH) lookup_flags |= LOOKUP_EMPTY; + + if (how->resolve & RESOLVE_NO_XDEV) + lookup_flags |= LOOKUP_NO_XDEV; + if (how->resolve & RESOLVE_NO_MAGICLINKS) + lookup_flags |= LOOKUP_NO_MAGICLINKS; + if (how->resolve & RESOLVE_NO_SYMLINKS) + lookup_flags |= LOOKUP_NO_SYMLINKS; + if (how->resolve & RESOLVE_BENEATH) + lookup_flags |= LOOKUP_BENEATH; + if (how->resolve & RESOLVE_IN_ROOT) + lookup_flags |= LOOKUP_IN_ROOT; + op->lookup_flags = lookup_flags; return 0; } @@ -1035,8 +1064,14 @@ static inline int build_open_flags(int flags, umode_t mode, struct open_flags *o struct file *file_open_name(struct filename *name, int flags, umode_t mode) { struct open_flags op; - int err = build_open_flags(flags, mode, &op); - return err ? ERR_PTR(err) : do_filp_open(AT_FDCWD, name, &op); + struct open_how how = { + .flags = flags & VALID_OPEN_FLAGS, + .mode = OPENHOW_MODE(flags, mode), + }; + int err = build_open_flags(&how, &op); + if (err) + return ERR_PTR(err); + return do_filp_open(AT_FDCWD, name, &op); }
/** @@ -1067,17 +1102,22 @@ struct file *file_open_root(struct dentry *dentry, struct vfsmount *mnt, const char *filename, int flags, umode_t mode) { struct open_flags op; - int err = build_open_flags(flags, mode, &op); + struct open_how how = { + .flags = flags & VALID_OPEN_FLAGS, + .mode = OPENHOW_MODE(flags, mode), + }; + int err = build_open_flags(&how, &op); if (err) return ERR_PTR(err); return do_file_open_root(dentry, mnt, filename, &op); } EXPORT_SYMBOL(file_open_root);
-long do_sys_open(int dfd, const char __user *filename, int flags, umode_t mode) +long do_sys_open(int dfd, const char __user *filename, + struct open_how *how) { struct open_flags op; - int fd = build_open_flags(flags, mode, &op); + int fd = build_open_flags(how, &op); int empty = 0; struct filename *tmp;
@@ -1090,7 +1130,7 @@ long do_sys_open(int dfd, const char __user *filename, int flags, umode_t mode) if (!empty) op.open_flag &= ~O_EMPTYPATH;
- fd = get_unused_fd_flags(flags); + fd = get_unused_fd_flags(how->flags); if (fd >= 0) { struct file *f = do_filp_open(dfd, tmp, &op); if (IS_ERR(f)) { @@ -1107,19 +1147,35 @@ long do_sys_open(int dfd, const char __user *filename, int flags, umode_t mode)
SYSCALL_DEFINE3(open, const char __user *, filename, int, flags, umode_t, mode) { - if (force_o_largefile()) - flags |= O_LARGEFILE; - - return do_sys_open(AT_FDCWD, filename, flags, mode); + return ksys_open(filename, flags, mode); }
SYSCALL_DEFINE4(openat, int, dfd, const char __user *, filename, int, flags, umode_t, mode) { + struct open_how how = { + .flags = flags & VALID_OPEN_FLAGS, + .mode = OPENHOW_MODE(flags, mode), + }; + + if (force_o_largefile()) + how.flags |= O_LARGEFILE; + + return do_sys_open(dfd, filename, &how); +} + +SYSCALL_DEFINE3(openat2, int, dfd, const char __user *, filename, + const struct open_how __user *, how) +{ + struct open_how tmp; + + if (copy_from_user(&tmp, how, sizeof(tmp))) + return -EFAULT; + if (force_o_largefile()) - flags |= O_LARGEFILE; + tmp.flags |= O_LARGEFILE;
- return do_sys_open(dfd, filename, flags, mode); + return do_sys_open(dfd, filename, &tmp); }
#ifdef CONFIG_COMPAT @@ -1129,7 +1185,11 @@ SYSCALL_DEFINE4(openat, int, dfd, const char __user *, filename, int, flags, */ COMPAT_SYSCALL_DEFINE3(open, const char __user *, filename, int, flags, umode_t, mode) { - return do_sys_open(AT_FDCWD, filename, flags, mode); + struct open_how how = { + .flags = flags & VALID_OPEN_FLAGS, + .mode = OPENHOW_MODE(flags, mode), + }; + return do_sys_open(AT_FDCWD, filename, &how); }
/* @@ -1138,7 +1198,11 @@ COMPAT_SYSCALL_DEFINE3(open, const char __user *, filename, int, flags, umode_t, */ COMPAT_SYSCALL_DEFINE4(openat, int, dfd, const char __user *, filename, int, flags, umode_t, mode) { - return do_sys_open(dfd, filename, flags, mode); + struct open_how how = { + .flags = flags & VALID_OPEN_FLAGS, + .mode = OPENHOW_MODE(flags, mode), + }; + return do_sys_open(dfd, filename, &how); } #endif
diff --git a/include/linux/fcntl.h b/include/linux/fcntl.h index 2868ae6c8fc1..f7f378e1f43c 100644 --- a/include/linux/fcntl.h +++ b/include/linux/fcntl.h @@ -4,13 +4,26 @@
#include <uapi/linux/fcntl.h>
-/* list of all valid flags for the open/openat flags argument: */ +/* Should open_how.mode be set for older syscalls wrappers? */ +#define OPENHOW_MODE(flags, mode) \ + (((flags) & (O_CREAT | __O_TMPFILE)) ? (mode) : 0) + +/* List of all valid flags for the open/openat flags argument: */ #define VALID_OPEN_FLAGS \ (O_RDONLY | O_WRONLY | O_RDWR | O_CREAT | O_EXCL | O_NOCTTY | O_TRUNC | \ O_APPEND | O_NDELAY | O_NONBLOCK | O_NDELAY | __O_SYNC | O_DSYNC | \ FASYNC | O_DIRECT | O_LARGEFILE | O_DIRECTORY | O_NOFOLLOW | \ O_NOATIME | O_CLOEXEC | O_PATH | __O_TMPFILE | O_EMPTYPATH)
+/* List of all valid flags for the how->upgrade_mask argument: */ +#define VALID_UPGRADE_FLAGS \ + (UPGRADE_NOWRITE | UPGRADE_NOREAD) + +/* List of all valid flags for the how->resolve argument: */ +#define VALID_RESOLVE_FLAGS \ + (RESOLVE_NO_XDEV | RESOLVE_NO_MAGICLINKS | RESOLVE_NO_SYMLINKS | \ + RESOLVE_BENEATH | RESOLVE_IN_ROOT) + #ifndef force_o_largefile #define force_o_largefile() (!IS_ENABLED(CONFIG_ARCH_32BIT_OFF_T)) #endif diff --git a/include/linux/fs.h b/include/linux/fs.h index a9ad596b28e2..135e4fa773fc 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -2498,8 +2498,8 @@ extern int do_truncate(struct dentry *, loff_t start, unsigned int time_attrs, struct file *filp); extern int vfs_fallocate(struct file *file, int mode, loff_t offset, loff_t len); -extern long do_sys_open(int dfd, const char __user *filename, int flags, - umode_t mode); +extern long do_sys_open(int dfd, const char __user *filename, + struct open_how *how); extern struct file *file_open_name(struct filename *, int, umode_t); extern struct file *filp_open(const char *, int, umode_t); extern struct file *file_open_root(struct dentry *, struct vfsmount *, diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h index 88145da7d140..a4f2f135001e 100644 --- a/include/linux/syscalls.h +++ b/include/linux/syscalls.h @@ -69,6 +69,7 @@ struct rseq; union bpf_attr; struct io_uring_params; struct clone_args; +struct open_how;
#include <linux/types.h> #include <linux/aio_abi.h> @@ -439,6 +440,8 @@ asmlinkage long sys_fchownat(int dfd, const char __user *filename, uid_t user, asmlinkage long sys_fchown(unsigned int fd, uid_t user, gid_t group); asmlinkage long sys_openat(int dfd, const char __user *filename, int flags, umode_t mode); +asmlinkage long sys_openat2(int dfd, const char __user *filename, + const struct open_how *how); asmlinkage long sys_close(unsigned int fd); asmlinkage long sys_vhangup(void);
@@ -1374,15 +1377,21 @@ static inline int ksys_close(unsigned int fd) return __close_fd(current->files, fd); }
-extern long do_sys_open(int dfd, const char __user *filename, int flags, - umode_t mode); +extern long do_sys_open(int dfd, const char __user *filename, + struct open_how *how);
static inline long ksys_open(const char __user *filename, int flags, umode_t mode) { + struct open_how how = { + .flags = flags & VALID_OPEN_FLAGS, + .mode = OPENHOW_MODE(flags, mode), + }; + if (force_o_largefile()) - flags |= O_LARGEFILE; - return do_sys_open(AT_FDCWD, filename, flags, mode); + how.flags |= O_LARGEFILE; + + return do_sys_open(AT_FDCWD, filename, &how); }
extern long do_sys_truncate(const char __user *pathname, loff_t length); diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h index 1be0e798e362..b28c11b338ee 100644 --- a/include/uapi/asm-generic/unistd.h +++ b/include/uapi/asm-generic/unistd.h @@ -851,8 +851,11 @@ __SYSCALL(__NR_pidfd_open, sys_pidfd_open) __SYSCALL(__NR_clone3, sys_clone3) #endif
+#define __NR_openat2 437 +__SYSCALL(__NR_openat2, sys_openat2) + #undef __NR_syscalls -#define __NR_syscalls 436 +#define __NR_syscalls 438
/* * 32 bit systems traditionally used different diff --git a/include/uapi/linux/fcntl.h b/include/uapi/linux/fcntl.h index 1d338357df8a..ebfc97b3d8aa 100644 --- a/include/uapi/linux/fcntl.h +++ b/include/uapi/linux/fcntl.h @@ -93,5 +93,47 @@
#define AT_RECURSIVE 0x8000 /* Apply to the entire subtree */
+/** + * Arguments for how openat2(2) should open the target path. If @resolve is + * zero, then openat2(2) operates identically to openat(2). + * + * However, unlike openat(2), unknown bits in @flags result in -EINVAL rather + * than being silently ignored. In addition, @mode (or @upgrade_mask) must be + * zero unless one of {O_CREAT, O_TMPFILE, O_PATH} are set. + * + * @flags: O_* flags. + * @mode: O_CREAT/O_TMPFILE file mode. + * @upgrade_mask: UPGRADE_* flags (to restrict O_PATH re-opening). + * @resolve: RESOLVE_* flags. + * @reserved: reserved for future extensions, must be zeroed. + */ +struct open_how { + __u32 flags; + union { + __u16 mode; + __u16 upgrade_mask; + }; + __u16 resolve; + __u64 reserved[7]; /* must be zeroed */ +}; + +/* how->resolve flags for openat2(2). */ +#define RESOLVE_NO_XDEV 0x01 /* Block mount-point crossings + (includes bind-mounts). */ +#define RESOLVE_NO_MAGICLINKS 0x02 /* Block traversal through procfs-style + "magic-links". */ +#define RESOLVE_NO_SYMLINKS 0x04 /* Block traversal through all symlinks + (implies OEXT_NO_MAGICLINKS) */ +#define RESOLVE_BENEATH 0x08 /* Block "lexical" trickery like + "..", symlinks, and absolute + paths which escape the dirfd. */ +#define RESOLVE_IN_ROOT 0x10 /* Make all jumps to "/" and ".." + be scoped inside the dirfd + (similar to chroot(2)). */ + +/* how->upgrade flags for openat2(2). */ +/* First bit is reserved for a future UPGRADE_NOEXEC flag. */ +#define UPGRADE_NOREAD 0x02 /* Block re-opening with MAY_READ. */ +#define UPGRADE_NOWRITE 0x04 /* Block re-opening with MAY_WRITE. */
#endif /* _UAPI_LINUX_FCNTL_H */
On Mon, Aug 19, 2019 at 8:37 PM Aleksa Sarai cyphar@cyphar.com wrote:
The most obvious syscall to add support for the new LOOKUP_* scoping flags would be openat(2). However, there are a few reasons why this is not the best course of action:
The new LOOKUP_* flags are intended to be security features, and openat(2) will silently ignore all unknown flags. This means that users would need to avoid foot-gunning themselves constantly when using this interface if it were part of openat(2). This can be fixed by having userspace libraries handle this for users[1], but should be avoided if possible.
Resolution scoping feels like a different operation to the existing O_* flags. And since openat(2) has limited flag space, it seems to be quite wasteful to clutter it with 5 flags that are all resolution-related. Arguably O_NOFOLLOW is also a resolution flag but its entire purpose is to error out if you encounter a trailing symlink -- not to scope resolution.
Other systems would be able to reimplement this syscall allowing for cross-OS standardisation rather than being hidden amongst O_* flags which may result in it not being used by all the parties that might want to use it (file servers, web servers, container runtimes, etc).
It gives us the opportunity to iterate on the O_PATH interface. In particular, the new @how->upgrade_mask field for fd re-opening is only possible because we have a clean slate without needing to re-use the ACC_MODE flag design nor the existing openat(2) @mode semantics.
To this end, we introduce the openat2(2) syscall. It provides all of the features of openat(2) through the @how->flags argument, but also also provides a new @how->resolve argument which exposes RESOLVE_* flags that map to our new LOOKUP_* flags. It also eliminates the long-standing ugliness of variadic-open(2) by embedding it in a struct.
In order to allow for userspace to lock down their usage of file descriptor re-opening, openat2(2) has the ability for users to disallow certain re-opening modes through @how->upgrade_mask. At the moment, there is no UPGRADE_NOEXEC. The open_how struct is padded to 64 bytes for future extensions (all of the reserved bits must be zeroed).
Why pad the structure when new functionality (perhaps accommodated via a larger structure) could be signaled by passing a new flag? Adding reserved fields to a structure with a size embedded in the ABI makes a lot of sense --- e.g., pthread_mutex_t can't grow. But this structure can grow, so the reservation seems needless to me.
On 2019-08-24, Daniel Colascione dancol@google.com wrote:
On Mon, Aug 19, 2019 at 8:37 PM Aleksa Sarai cyphar@cyphar.com wrote:
The most obvious syscall to add support for the new LOOKUP_* scoping flags would be openat(2). However, there are a few reasons why this is not the best course of action:
The new LOOKUP_* flags are intended to be security features, and openat(2) will silently ignore all unknown flags. This means that users would need to avoid foot-gunning themselves constantly when using this interface if it were part of openat(2). This can be fixed by having userspace libraries handle this for users[1], but should be avoided if possible.
Resolution scoping feels like a different operation to the existing O_* flags. And since openat(2) has limited flag space, it seems to be quite wasteful to clutter it with 5 flags that are all resolution-related. Arguably O_NOFOLLOW is also a resolution flag but its entire purpose is to error out if you encounter a trailing symlink -- not to scope resolution.
Other systems would be able to reimplement this syscall allowing for cross-OS standardisation rather than being hidden amongst O_* flags which may result in it not being used by all the parties that might want to use it (file servers, web servers, container runtimes, etc).
It gives us the opportunity to iterate on the O_PATH interface. In particular, the new @how->upgrade_mask field for fd re-opening is only possible because we have a clean slate without needing to re-use the ACC_MODE flag design nor the existing openat(2) @mode semantics.
To this end, we introduce the openat2(2) syscall. It provides all of the features of openat(2) through the @how->flags argument, but also also provides a new @how->resolve argument which exposes RESOLVE_* flags that map to our new LOOKUP_* flags. It also eliminates the long-standing ugliness of variadic-open(2) by embedding it in a struct.
In order to allow for userspace to lock down their usage of file descriptor re-opening, openat2(2) has the ability for users to disallow certain re-opening modes through @how->upgrade_mask. At the moment, there is no UPGRADE_NOEXEC. The open_how struct is padded to 64 bytes for future extensions (all of the reserved bits must be zeroed).
Why pad the structure when new functionality (perhaps accommodated via a larger structure) could be signaled by passing a new flag? Adding reserved fields to a structure with a size embedded in the ABI makes a lot of sense --- e.g., pthread_mutex_t can't grow. But this structure can grow, so the reservation seems needless to me.
Quite a few folks have said that ->reserved is either unnecessary or too big. I will be changing this, though I am not clear what the best way of extending the structure is. If anyone has a strong opinion on this (or an alternative to the ones listed below), please chime in. I don't have any really strong attachment to this aspect of the API.
There appear to be a few ways we can do it (that all have precedence with other syscalls):
1. Use O_* flags to indicate extensions. 2. A separate "version" field that is incremented when we change. 3. Add a size_t argument to openat2(2). 4. Reserve space (as in this patchset).
(My personal preference would be (3), followed closely by (2).)
The main problem with (1) is that it pollutes the open(2) and openat(2) syscalls with new O_* flags, which is probably not a good API decision (syscall flags are already "bad" enough, let's not throw a bunch of no-ops into the mix).
(2) is mostly fine except for a slight issue of ergonomics (glibc would have to auto-fill the version field or make wrappers in order to make it easier to use sanely). But this does have the benefit that we could re-arrange fields (not that this is something we'd want to do anyway).
Both (1) and (2) have the problem that the "struct version" is inside the struct so we'd need to copy_from_user() twice. This isn't the end of the world, it just feels a bit less clean than is ideal. (3) fixes that problem, at the cost of making the API slightly more cumbersome to use directly (though again glibc could wrap that away).
And the downsides of (4) are pretty well discussed already.
On 29/08/2019 14.15, Aleksa Sarai wrote:
On 2019-08-24, Daniel Colascione dancol@google.com wrote:
Why pad the structure when new functionality (perhaps accommodated via a larger structure) could be signaled by passing a new flag? Adding reserved fields to a structure with a size embedded in the ABI makes a lot of sense --- e.g., pthread_mutex_t can't grow. But this structure can grow, so the reservation seems needless to me.
Quite a few folks have said that ->reserved is either unnecessary or too big. I will be changing this, though I am not clear what the best way of extending the structure is. If anyone has a strong opinion on this (or an alternative to the ones listed below), please chime in. I don't have any really strong attachment to this aspect of the API.
There appear to be a few ways we can do it (that all have precedence with other syscalls):
- Use O_* flags to indicate extensions.
- A separate "version" field that is incremented when we change.
- Add a size_t argument to openat2(2).
- Reserve space (as in this patchset).
(My personal preference would be (3), followed closely by (2).)
3, definitely, and instead of having to invent a new scheme for every new syscall, make that the default pattern by providing a helper
int __copy_abi_struct(void *kernel, size_t ksize, const void __user *user, size_t usize) { size_t copy = min(ksize, usize);
if (copy_from_user(kernel, user, copy)) return -EFAULT;
if (usize > ksize) { /* maybe a separate "return user_is_zero(user + ksize, usize - ksize);" helper */ char c; user += ksize; usize -= ksize; while (usize--) { if (get_user(c, user++)) return -EFAULT; if (c) return -EINVAL; } } else if (ksize > usize) { memset(kernel + usize, 0, ksize - usize); } return 0; } #define copy_abi_struct(kernel, user, usize) \ __copy_abi_struct(kernel, sizeof(*kernel), user, usize)
Both (1) and (2) have the problem that the "struct version" is inside the struct so we'd need to copy_from_user() twice. This isn't the end of the world, it just feels a bit less clean than is ideal. (3) fixes that problem, at the cost of making the API slightly more cumbersome to use directly (though again glibc could wrap that away).
I don't see how 3 is cumbersome to use directly. Userspace code does struct openat_of_the_day args = {.field1 = x, .field3 = y} and passes &args, sizeof(args). What does glibc need to do beyond its usual munging of the userspace ABI registers to the syscall ABI registers?
Rasmus
On 2019-08-29, Rasmus Villemoes linux@rasmusvillemoes.dk wrote:
On 29/08/2019 14.15, Aleksa Sarai wrote:
On 2019-08-24, Daniel Colascione dancol@google.com wrote:
Why pad the structure when new functionality (perhaps accommodated via a larger structure) could be signaled by passing a new flag? Adding reserved fields to a structure with a size embedded in the ABI makes a lot of sense --- e.g., pthread_mutex_t can't grow. But this structure can grow, so the reservation seems needless to me.
Quite a few folks have said that ->reserved is either unnecessary or too big. I will be changing this, though I am not clear what the best way of extending the structure is. If anyone has a strong opinion on this (or an alternative to the ones listed below), please chime in. I don't have any really strong attachment to this aspect of the API.
There appear to be a few ways we can do it (that all have precedence with other syscalls):
- Use O_* flags to indicate extensions.
- A separate "version" field that is incremented when we change.
- Add a size_t argument to openat2(2).
- Reserve space (as in this patchset).
(My personal preference would be (3), followed closely by (2).)
3, definitely, and instead of having to invent a new scheme for every new syscall, make that the default pattern by providing a helper
Sure (though hopefully I don't need to immediately go and refactor all the existing size_t syscalls). I will be presenting about this patchset at the containers microconference at LPC (in a few weeks), so I'll hold of on any API-related rewrites until after that.
int __copy_abi_struct(void *kernel, size_t ksize, const void __user *user, size_t usize) { size_t copy = min(ksize, usize);
if (copy_from_user(kernel, user, copy)) return -EFAULT;
if (usize > ksize) { /* maybe a separate "return user_is_zero(user + ksize, usize - ksize);" helper */ char c; user += ksize; usize -= ksize; while (usize--) { if (get_user(c, user++)) return -EFAULT; if (c) return -EINVAL;
This part would probably be better done with memchr_inv() and copy_from_user() (and probably should put an upper limit on usize), but I get what you mean.
}} else if (ksize > usize) { memset(kernel + usize, 0, ksize - usize); } return 0; } #define copy_abi_struct(kernel, user, usize) \ __copy_abi_struct(kernel, sizeof(*kernel), user, usize)
Both (1) and (2) have the problem that the "struct version" is inside the struct so we'd need to copy_from_user() twice. This isn't the end of the world, it just feels a bit less clean than is ideal. (3) fixes that problem, at the cost of making the API slightly more cumbersome to use directly (though again glibc could wrap that away).
I don't see how 3 is cumbersome to use directly. Userspace code does struct openat_of_the_day args = {.field1 = x, .field3 = y} and passes &args, sizeof(args). What does glibc need to do beyond its usual munging of the userspace ABI registers to the syscall ABI registers?
I'd argue that
ret = openat2(AT_FDCWD, "foo", &how, sizeof(how)); // (3)
is slightly less pretty than
ret = openat2(AT_FDCWD, "foo", &how); // (1), (2), (4)
But it's not really that bad. Forget I said anything.
Test all of the various openat2(2) flags, as well as how file descriptor re-opening works. A small stress-test of a symlink-rename attack is included to show that the protections against ".."-based attacks are sufficient.
In addition, the memfd selftest is fixed to no longer depend on the now-disallowed functionality of upgrading an O_RDONLY descriptor to O_RDWR.
Signed-off-by: Aleksa Sarai cyphar@cyphar.com --- tools/testing/selftests/Makefile | 1 + tools/testing/selftests/memfd/memfd_test.c | 7 +- tools/testing/selftests/openat2/.gitignore | 1 + tools/testing/selftests/openat2/Makefile | 8 + tools/testing/selftests/openat2/helpers.c | 162 +++++++ tools/testing/selftests/openat2/helpers.h | 116 +++++ .../testing/selftests/openat2/linkmode_test.c | 333 +++++++++++++++ .../selftests/openat2/rename_attack_test.c | 127 ++++++ .../testing/selftests/openat2/resolve_test.c | 402 ++++++++++++++++++ 9 files changed, 1155 insertions(+), 2 deletions(-) create mode 100644 tools/testing/selftests/openat2/.gitignore create mode 100644 tools/testing/selftests/openat2/Makefile create mode 100644 tools/testing/selftests/openat2/helpers.c create mode 100644 tools/testing/selftests/openat2/helpers.h create mode 100644 tools/testing/selftests/openat2/linkmode_test.c create mode 100644 tools/testing/selftests/openat2/rename_attack_test.c create mode 100644 tools/testing/selftests/openat2/resolve_test.c
diff --git a/tools/testing/selftests/Makefile b/tools/testing/selftests/Makefile index 25b43a8c2b15..13c02e0d0efc 100644 --- a/tools/testing/selftests/Makefile +++ b/tools/testing/selftests/Makefile @@ -37,6 +37,7 @@ TARGETS += powerpc TARGETS += proc TARGETS += pstore TARGETS += ptrace +TARGETS += openat2 TARGETS += rseq TARGETS += rtc TARGETS += seccomp diff --git a/tools/testing/selftests/memfd/memfd_test.c b/tools/testing/selftests/memfd/memfd_test.c index c67d32eeb668..e71df3d3e55d 100644 --- a/tools/testing/selftests/memfd/memfd_test.c +++ b/tools/testing/selftests/memfd/memfd_test.c @@ -925,7 +925,7 @@ static void test_share_mmap(char *banner, char *b_suffix) */ static void test_share_open(char *banner, char *b_suffix) { - int fd, fd2; + int procfd, fd, fd2;
printf("%s %s %s\n", memfd_str, banner, b_suffix);
@@ -950,13 +950,16 @@ static void test_share_open(char *banner, char *b_suffix) mfd_assert_has_seals(fd, F_SEAL_WRITE | F_SEAL_SHRINK); mfd_assert_has_seals(fd2, F_SEAL_WRITE | F_SEAL_SHRINK);
+ /* We cannot do a MAY_WRITE re-open of an O_RDONLY fd. */ + procfd = mfd_assert_open(fd2, O_PATH, 0); close(fd2); - fd2 = mfd_assert_open(fd, O_RDWR, 0); + fd2 = mfd_assert_open(procfd, O_WRONLY, 0);
mfd_assert_add_seals(fd2, F_SEAL_SEAL); mfd_assert_has_seals(fd, F_SEAL_WRITE | F_SEAL_SHRINK | F_SEAL_SEAL); mfd_assert_has_seals(fd2, F_SEAL_WRITE | F_SEAL_SHRINK | F_SEAL_SEAL);
+ close(procfd); close(fd2); close(fd); } diff --git a/tools/testing/selftests/openat2/.gitignore b/tools/testing/selftests/openat2/.gitignore new file mode 100644 index 000000000000..bd68f6c3fd07 --- /dev/null +++ b/tools/testing/selftests/openat2/.gitignore @@ -0,0 +1 @@ +/*_test diff --git a/tools/testing/selftests/openat2/Makefile b/tools/testing/selftests/openat2/Makefile new file mode 100644 index 000000000000..a0c1b53fd268 --- /dev/null +++ b/tools/testing/selftests/openat2/Makefile @@ -0,0 +1,8 @@ +# SPDX-License-Identifier: GPL-2.0 + +CFLAGS += -Wall -O2 -g +TEST_GEN_PROGS := linkmode_test resolve_test rename_attack_test + +include ../lib.mk + +$(TEST_GEN_PROGS): helpers.c diff --git a/tools/testing/selftests/openat2/helpers.c b/tools/testing/selftests/openat2/helpers.c new file mode 100644 index 000000000000..b9b7c7fc7a99 --- /dev/null +++ b/tools/testing/selftests/openat2/helpers.c @@ -0,0 +1,162 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * Author: Aleksa Sarai cyphar@cyphar.com + * Copyright (C) 2018-2019 SUSE LLC. + */ + +#define _GNU_SOURCE +#include <errno.h> +#include <fcntl.h> +#include <stdbool.h> +#include <string.h> +#include <syscall.h> +#include <limits.h> + +#include "helpers.h" + +int sys_openat2(int dfd, const char *path, const struct open_how *how) +{ + int ret = syscall(__NR_openat2, dfd, path, how); + return ret >= 0 ? ret : -errno; +} + +int sys_openat(int dfd, const char *path, const struct open_how *how) +{ + int ret = openat(dfd, path, how->flags, how->mode); + return ret >= 0 ? ret : -errno; +} + +int sys_renameat2(int olddirfd, const char *oldpath, + int newdirfd, const char *newpath, unsigned int flags) +{ + int ret = syscall(__NR_renameat2, olddirfd, oldpath, + newdirfd, newpath, flags); + return ret >= 0 ? ret : -errno; +} + +char *openat_flags(unsigned int flags) +{ + char *flagset, *accmode = "(none)"; + + switch (flags & 0x03) { + case O_RDWR: + accmode = "O_RDWR"; + break; + case O_RDONLY: + accmode = "O_RDONLY"; + break; + case O_WRONLY: + accmode = "O_WRONLY"; + break; + } + + E_asprintf(&flagset, "%s%s%s", + (flags & O_PATH) ? "O_PATH|" : "", + (flags & O_CREAT) ? "O_CREAT|" : "", + accmode); + + return flagset; +} + +char *openat2_flags(const struct open_how *how) +{ + char *p; + char *flags_set, *resolve_set, *acc_set, *set; + + flags_set = openat_flags(how->flags); + + E_asprintf(&resolve_set, "%s%s%s%s%s0", + (how->resolve & RESOLVE_NO_XDEV) ? "RESOLVE_NO_XDEV|" : "", + (how->resolve & RESOLVE_NO_MAGICLINKS) ? "RESOLVE_NO_MAGICLINKS|" : "", + (how->resolve & RESOLVE_NO_SYMLINKS) ? "RESOLVE_NO_SYMLINKS|" : "", + (how->resolve & RESOLVE_BENEATH) ? "RESOLVE_BENEATH|" : "", + (how->resolve & RESOLVE_IN_ROOT) ? "RESOLVE_IN_ROOT|" : ""); + + /* Remove trailing "|0". */ + p = strstr(resolve_set, "|0"); + if (p) + *p = '\0'; + + if (how->flags & O_PATH) + E_asprintf(&acc_set, ", upgrade_mask=%s%s0", + (how->upgrade_mask & UPGRADE_NOREAD) ? "UPGRADE_NOREAD|" : "", + (how->upgrade_mask & UPGRADE_NOWRITE) ? "UPGRADE_NOWRITE|" : ""); + else if (how->flags & O_CREAT) + E_asprintf(&acc_set, ", mode=0%o", how->mode); + else + acc_set = strdup(""); + + /* Remove trailing "|0". */ + p = strstr(acc_set, "|0"); + if (p) + *p = '\0'; + + /* And now generate our flagset. */ + E_asprintf(&set, "[flags=%s, resolve=%s%s]", + flags_set, resolve_set, acc_set); + + free(flags_set); + free(resolve_set); + free(acc_set); + return set; +} + +int touchat(int dfd, const char *path) +{ + int fd = openat(dfd, path, O_CREAT); + if (fd >= 0) + close(fd); + return fd; +} + +char *fdreadlink(int fd) +{ + char *target, *tmp; + + E_asprintf(&tmp, "/proc/self/fd/%d", fd); + + target = malloc(PATH_MAX); + if (!target) + ksft_exit_fail_msg("fdreadlink: malloc failed\n"); + memset(target, 0, PATH_MAX); + + E_readlink(tmp, target, PATH_MAX); + free(tmp); + return target; +} + +bool fdequal(int fd, int dfd, const char *path) +{ + char *fdpath, *dfdpath, *other; + bool cmp; + + fdpath = fdreadlink(fd); + dfdpath = fdreadlink(dfd); + + if (!path) + E_asprintf(&other, "%s", dfdpath); + else if (*path == '/') + E_asprintf(&other, "%s", path); + else + E_asprintf(&other, "%s/%s", dfdpath, path); + + cmp = !strcmp(fdpath, other); + if (!cmp) + ksft_print_msg("fdequal: expected '%s' but got '%s'\n", other, fdpath); + + free(fdpath); + free(dfdpath); + free(other); + return cmp; +} + +void test_openat2_supported(void) +{ + struct open_how how = {}; + int fd = sys_openat2(AT_FDCWD, ".", &how); + if (fd == -ENOSYS) + ksft_exit_skip("openat2(2) unsupported on this kernel\n"); + if (fd < 0) + ksft_exit_fail_msg("openat2(2) supported check failed: %s\n", strerror(-fd)); + close(fd); +} diff --git a/tools/testing/selftests/openat2/helpers.h b/tools/testing/selftests/openat2/helpers.h new file mode 100644 index 000000000000..43fa7835950f --- /dev/null +++ b/tools/testing/selftests/openat2/helpers.h @@ -0,0 +1,116 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * Author: Aleksa Sarai cyphar@cyphar.com + * Copyright (C) 2018-2019 SUSE LLC. + */ + +#ifndef __RESOLVEAT_H__ +#define __RESOLVEAT_H__ + +#define _GNU_SOURCE +#include <stdint.h> +#include <errno.h> +#include "../kselftest.h" + +#define ARRAY_LEN(X) (sizeof (X) / sizeof (*(X))) +#define BUILD_BUG_ON(e) ((void)(sizeof(struct { int:(-!!(e)); }))) + +#ifndef SYS_openat2 +#ifndef __NR_openat2 +#define __NR_openat2 437 +#endif /* __NR_openat2 */ +#define SYS_openat2 __NR_openat2 +#endif /* SYS_openat2 */ + +/** + * Arguments for how openat2(2) should open the target path. If @extra is zero, + * then openat2 is identical to openat(2). Only one of @mode or @upgrade_mask + * may be set at any given time. + * + * @flags: O_* flags (unknown flags ignored). + * @mode: O_CREAT file mode (ignored otherwise). + * @upgrade_mask: restrict how the O_PATH may be re-opened (ignored otherwise). + * @resolve: RESOLVE_* flags (-EINVAL on unknown flags). + * @reserved: reserved for future extensions, must be zeroed. + */ +struct open_how { + uint32_t flags; + union { + uint16_t mode; + uint16_t upgrade_mask; + }; + uint16_t resolve; + uint64_t reserved[7]; /* must be zeroed */ +}; + +#ifndef RESOLVE_INROOT +/* how->resolve flags for openat2(2). */ +#define RESOLVE_NO_XDEV 0x01 /* Block mount-point crossings + (includes bind-mounts). */ +#define RESOLVE_NO_MAGICLINKS 0x02 /* Block traversal through procfs-style + "magic-links". */ +#define RESOLVE_NO_SYMLINKS 0x04 /* Block traversal through all symlinks + (implies OEXT_NO_MAGICLINKS) */ +#define RESOLVE_BENEATH 0x08 /* Block "lexical" trickery like + "..", symlinks, and absolute + paths which escape the dirfd. */ +#define RESOLVE_IN_ROOT 0x10 /* Make all jumps to "/" and ".." + be scoped inside the dirfd + (similar to chroot(2)). */ +#endif /* RESOLVE_IN_ROOT */ + +#ifndef UPGRADE_NOREAD +/* how->upgrade flags for openat2(2). */ +/* First bit is reserved for a future UPGRADE_NOEXEC flag. */ +#define UPGRADE_NOREAD 0x02 /* Block re-opening with MAY_READ. */ +#define UPGRADE_NOWRITE 0x04 /* Block re-opening with MAY_WRITE. */ +#endif /* UPGRADE_NOREAD */ + +#ifndef O_EMPTYPATH +#define O_EMPTYPATH 040000000 +#endif /* O_EMPTYPATH */ + +#define E_func(func, ...) \ + do { \ + if (func(__VA_ARGS__) < 0) \ + ksft_exit_fail_msg("%s:%d %s failed\n", \ + __FILE__, __LINE__, #func);\ + } while (0) + +#define E_mkdirat(...) E_func(mkdirat, __VA_ARGS__) +#define E_symlinkat(...) E_func(symlinkat, __VA_ARGS__) +#define E_touchat(...) E_func(touchat, __VA_ARGS__) +#define E_readlink(...) E_func(readlink, __VA_ARGS__) +#define E_fstatat(...) E_func(fstatat, __VA_ARGS__) +#define E_asprintf(...) E_func(asprintf, __VA_ARGS__) +#define E_fchdir(...) E_func(fchdir, __VA_ARGS__) +#define E_mount(...) E_func(mount, __VA_ARGS__) +#define E_unshare(...) E_func(unshare, __VA_ARGS__) +#define E_setresuid(...) E_func(setresuid, __VA_ARGS__) +#define E_chmod(...) E_func(chmod, __VA_ARGS__) + +#define E_assert(expr, msg, ...) \ + do { \ + if (!(expr)) \ + ksft_exit_fail_msg("ASSERT(%s:%d) failed (%s): " msg "\n", \ + __FILE__, __LINE__, #expr, ##__VA_ARGS__); \ + } while (0) + +typedef int (*openfunc_t)(int dfd, const char *path, const struct open_how *how); + +int sys_openat2(int dfd, const char *path, const struct open_how *how); +char *openat2_flags(const struct open_how *how); + +int sys_openat(int dfd, const char *path, const struct open_how *how); +char *openat_flags(unsigned int flags); + +int sys_renameat2(int olddirfd, const char *oldpath, + int newdirfd, const char *newpath, unsigned int flags); + +int touchat(int dfd, const char *path); +char *fdreadlink(int fd); +bool fdequal(int fd, int dfd, const char *path); + +void test_openat2_supported(void); + +#endif /* __RESOLVEAT_H__ */ diff --git a/tools/testing/selftests/openat2/linkmode_test.c b/tools/testing/selftests/openat2/linkmode_test.c new file mode 100644 index 000000000000..44fcba738686 --- /dev/null +++ b/tools/testing/selftests/openat2/linkmode_test.c @@ -0,0 +1,333 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * Author: Aleksa Sarai cyphar@cyphar.com + * Copyright (C) 2018-2019 SUSE LLC. + */ + +#define _GNU_SOURCE +#include <fcntl.h> +#include <sys/stat.h> +#include <sys/types.h> +#include <stdbool.h> +#include <string.h> + +#include "../kselftest.h" +#include "helpers.h" + +static mode_t fdmode(int fd) +{ + char *fdpath; + struct stat statbuf; + mode_t mode; + + E_asprintf(&fdpath, "/proc/self/fd/%d", fd); + E_fstatat(AT_FDCWD, fdpath, &statbuf, AT_SYMLINK_NOFOLLOW); + mode = (statbuf.st_mode & ~S_IFMT); + free(fdpath); + + return mode; +} + +static int reopen_proc(int fd, unsigned int flags) +{ + int ret, saved_errno; + char *fdpath; + + E_asprintf(&fdpath, "/proc/self/fd/%d", fd); + ret = open(fdpath, flags); + saved_errno = errno; + free(fdpath); + + return ret >= 0 ? ret : -saved_errno; +} + +static int reopen_oemptypath(int fd, unsigned int flags) +{ + int ret = openat(fd, "", O_EMPTYPATH | flags); + return ret >= 0 ? ret : -errno; +} + +struct reopen_test { + openfunc_t open; + mode_t chmod_mode; + struct { + struct open_how how; + mode_t mode; + int err; + } orig, new; +}; + +static bool reopen(int fd, struct reopen_test *test) +{ + int newfd; + mode_t proc_mode; + bool failed = false; + + /* Check that the proc mode is correct. */ + proc_mode = fdmode(fd); + if (proc_mode != test->orig.mode) { + ksft_print_msg("incorrect fdmode (got[%o] != want[%o])\n", + proc_mode, test->orig.mode); + failed = true; + } + + /* Re-open through /proc. */ + newfd = reopen_proc(fd, test->new.how.flags); + if (newfd != test->new.err && (newfd < 0 || test->new.err < 0)) { + ksft_print_msg("/proc failure (%d != %d [%s])\n", + newfd, test->new.err, strerror(-test->new.err)); + failed = true; + } + if (newfd >= 0) { + proc_mode = fdmode(newfd); + if (proc_mode != test->new.mode) { + ksft_print_msg("/proc wrong fdmode (got[%o] != want[%o])\n", + proc_mode, test->new.mode); + failed = true; + } + close(newfd); + } + + /* Re-open with O_EMPTYPATH. */ + newfd = reopen_oemptypath(fd, test->new.how.flags); + if (newfd != test->new.err && (newfd < 0 || test->new.err < 0)) { + ksft_print_msg("O_EMPTYPATH failure (%d != %d [%s])\n", + newfd, test->new.err, strerror(-test->new.err)); + failed = true; + } + if (newfd >= 0) { + proc_mode = fdmode(newfd); + if (proc_mode != test->new.mode) { + ksft_print_msg("O_EMPTYPATH wrong fdmode (got[%o] != want[%o])\n", + proc_mode, test->new.mode); + failed = true; + } + close(newfd); + } + + return failed; +} + +#define NUM_REOPEN_TESTS 28 + +void test_reopen_ordinary(bool privileged) +{ + int fd; + int err_access = privileged ? 0 : -EACCES; + char tmpfile[] = "/tmp/ksft-openat2-reopen-testfile.XXXXXX"; + + fd = mkstemp(tmpfile); + E_assert(fd >= 0, "mkstemp failed: %m\n"); + close(fd); + + struct reopen_test tests[] = { + /* Re-opening with the same mode should succeed. */ + { .open = sys_openat, .chmod_mode = 0400, + .orig.how.flags = O_RDONLY, .orig.mode = 0500, + .new.how.flags = O_RDONLY, .new.mode = 0500 }, + { .open = sys_openat, .chmod_mode = 0200, + .orig.how.flags = O_WRONLY, .orig.mode = 0300, + .new.how.flags = O_WRONLY, .new.mode = 0300 }, + { .open = sys_openat, .chmod_mode = 0600, + .orig.how.flags = O_RDWR, .orig.mode = 0700, + .new.how.flags = O_RDWR, .new.mode = 0700 }, + { .open = sys_openat, .chmod_mode = 0600, + .orig.how.flags = O_RDWR, .orig.mode = 0700, + .new.how.flags = O_RDONLY, .new.mode = 0500 }, + { .open = sys_openat, .chmod_mode = 0600, + .orig.how.flags = O_RDWR, .orig.mode = 0700, + .new.how.flags = O_WRONLY, .new.mode = 0300 }, + + /* + * Re-opening with a different mode will always fail (with an obvious + * carve-out for privileged users). + */ + { .open = sys_openat, .chmod_mode = 0600, + .orig.how.flags = O_RDONLY, .orig.mode = 0500, + .new.how.flags = O_WRONLY, .new.mode = 0300, .new.err = err_access }, + { .open = sys_openat, .chmod_mode = 0600, + .orig.how.flags = O_WRONLY, .orig.mode = 0300, + .new.how.flags = O_RDONLY, .new.mode = 0500, .new.err = err_access }, + { .open = sys_openat, .chmod_mode = 0600, + .orig.how.flags = O_RDONLY, .orig.mode = 0500, + .new.how.flags = O_RDWR, .new.mode = 0700, .new.err = err_access }, + { .open = sys_openat, .chmod_mode = 0600, + .orig.how.flags = O_WRONLY, .orig.mode = 0300, + .new.how.flags = O_RDWR, .new.mode = 0700, .new.err = err_access }, + + /* Doubly so if they didn't even have permissions at open-time. */ + { .open = sys_openat, .chmod_mode = 0400, + .orig.how.flags = O_RDONLY, .orig.mode = 0500, + .new.how.flags = O_WRONLY, .new.mode = 0300, .new.err = err_access }, + { .open = sys_openat, .chmod_mode = 0200, + .orig.how.flags = O_WRONLY, .orig.mode = 0300, + .new.how.flags = O_RDONLY, .new.mode = 0500, .new.err = err_access }, + { .open = sys_openat, .chmod_mode = 0400, + .orig.how.flags = O_RDONLY, .orig.mode = 0500, + .new.how.flags = O_RDWR, .new.mode = 0700, .new.err = err_access }, + { .open = sys_openat, .chmod_mode = 0200, + .orig.how.flags = O_WRONLY, .orig.mode = 0300, + .new.how.flags = O_RDWR, .new.mode = 0700, .new.err = err_access }, + + /* O_PATH re-opens (of ordinary files) will always work. */ + { .open = sys_openat, .chmod_mode = 0000, + .orig.how.flags = O_PATH, .orig.mode = 0070, + .new.how.flags = O_WRONLY, .new.mode = 0300 }, + { .open = sys_openat2, .chmod_mode = 0000, + .orig.how.flags = O_PATH, .orig.mode = 0070, + .new.how.flags = O_WRONLY, .new.mode = 0300 }, + + { .open = sys_openat, .chmod_mode = 0000, + .orig.how.flags = O_PATH, .orig.mode = 0070, + .new.how.flags = O_RDONLY, .new.mode = 0500 }, + { .open = sys_openat2, .chmod_mode = 0000, + .orig.how.flags = O_PATH, .orig.mode = 0070, + .new.how.flags = O_RDONLY, .new.mode = 0500 }, + + { .open = sys_openat, .chmod_mode = 0000, + .orig.how.flags = O_PATH, .orig.mode = 0070, + .new.how.flags = O_RDWR, .new.mode = 0700 }, + { .open = sys_openat2, .chmod_mode = 0000, + .orig.how.flags = O_PATH, .orig.mode = 0070, + .new.how.flags = O_RDWR, .new.mode = 0700 }, + + /* + * openat2(2) UPGRADE_NO* flags. In the privileged case, the re-open + * will work but the mode will still be scoped to the mode (or'd with + * the open acc_mode). + */ + { .open = sys_openat2, .chmod_mode = 0000, + .orig.how.flags = O_PATH, .orig.mode = 0010, + .orig.how.upgrade_mask = UPGRADE_NOREAD | UPGRADE_NOWRITE, + .new.how.flags = O_RDONLY, .new.mode = 0500, .new.err = err_access }, + { .open = sys_openat2, .chmod_mode = 0000, + .orig.how.flags = O_PATH, .orig.mode = 0010, + .orig.how.upgrade_mask = UPGRADE_NOREAD | UPGRADE_NOWRITE, + .new.how.flags = O_WRONLY, .new.mode = 0300, .new.err = err_access }, + { .open = sys_openat2, .chmod_mode = 0000, + .orig.how.flags = O_PATH, .orig.mode = 0010, + .orig.how.upgrade_mask = UPGRADE_NOREAD | UPGRADE_NOWRITE, + .new.how.flags = O_RDWR, .new.mode = 0700, .new.err = err_access }, + + { .open = sys_openat2, .chmod_mode = 0000, + .orig.how.flags = O_PATH, .orig.mode = 0050, + .orig.how.upgrade_mask = UPGRADE_NOWRITE, + .new.how.flags = O_RDONLY, .new.mode = 0500 }, + + { .open = sys_openat2, .chmod_mode = 0000, + .orig.how.flags = O_PATH, .orig.mode = 0030, + .orig.how.upgrade_mask = UPGRADE_NOREAD, + .new.how.flags = O_WRONLY, .new.mode = 0300 }, + + { .open = sys_openat2, .chmod_mode = 0000, + .orig.how.flags = O_PATH, .orig.mode = 0030, + .orig.how.upgrade_mask = UPGRADE_NOREAD, + .new.how.flags = O_RDONLY, .new.mode = 0500, .new.err = err_access }, + { .open = sys_openat2, .chmod_mode = 0000, + .orig.how.flags = O_PATH, .orig.mode = 0050, + .orig.how.upgrade_mask = UPGRADE_NOWRITE, + .new.how.flags = O_WRONLY, .new.mode = 0300, .new.err = err_access }, + { .open = sys_openat2, .chmod_mode = 0000, + .orig.how.flags = O_PATH, .orig.mode = 0030, + .orig.how.upgrade_mask = UPGRADE_NOREAD, + .new.how.flags = O_RDWR, .new.mode = 0700, .new.err = err_access }, + { .open = sys_openat2, .chmod_mode = 0000, + .orig.how.flags = O_PATH, .orig.mode = 0050, + .orig.how.upgrade_mask = UPGRADE_NOWRITE, + .new.how.flags = O_RDWR, .new.mode = 0700, .new.err = err_access }, + }; + + BUILD_BUG_ON(ARRAY_LEN(tests) != NUM_REOPEN_TESTS); + + for (int i = 0; i < ARRAY_LEN(tests); i++) { + int fd; + char *orig_flagset, *new_flagset; + struct reopen_test *test = &tests[i]; + void (*resultfn)(const char *msg, ...) = ksft_test_result_pass; + + E_chmod(tmpfile, test->chmod_mode); + + fd = test->open(AT_FDCWD, tmpfile, &test->orig.how); + E_assert(fd >= 0, "open '%s' failed: %m\n", tmpfile); + + /* Make sure that any EACCES we see is not from inode permissions. */ + E_chmod(tmpfile, 0777); + + if (reopen(fd, test)) + resultfn = ksft_test_result_fail; + + close(fd); + + new_flagset = openat_flags(test->new.how.flags); + if (test->open == sys_openat) + orig_flagset = openat_flags(test->orig.how.flags); + else if (test->open == sys_openat2) + orig_flagset = openat2_flags(&test->orig.how); + else + ksft_exit_fail_msg("unknown test->open\n"); + + resultfn("%sordinary reopen of (orig[%s]=%s, new=%s) chmod=%.3o %s\n", + privileged ? "privileged " : "", + test->open == sys_openat ? "openat" : "openat2", + orig_flagset, new_flagset, test->chmod_mode, + test->new.err < 0 ? strerror(-test->new.err) : "works"); + fflush(stdout); + + free(new_flagset); + free(orig_flagset); + } + + unlink(tmpfile); +} + +#define NUM_CLOEXEC_TESTS 1 + +void test_openat2_cloexec_test(void) +{ + void (*resultfn)(const char *msg, ...) = ksft_test_result_pass; + struct open_how how = { + .flags = O_CLOEXEC | O_PATH | O_DIRECTORY, + }; + + int fd = sys_openat2(AT_FDCWD, ".", &how); + E_assert(fd >= 0, "open '.' failed: %m\n"); + + int flags = fcntl(fd, F_GETFD); + E_assert(flags >= 0, "F_GETFD failed: %m\n"); + + if (!(flags & FD_CLOEXEC)) + resultfn = ksft_test_result_fail; + + resultfn("openat2(O_CLOEXEC) works as expected\n"); +} + +int main(int argc, char **argv) +{ + bool privileged; + + ksft_print_header(); + ksft_set_plan(2 * NUM_REOPEN_TESTS + NUM_CLOEXEC_TESTS); + test_openat2_supported(); + + /* + * Technically we should be checking CAP_DAC_OVERRIDE, but it's easier to + * just assume that euid=0 has the full capability set. + */ + privileged = (geteuid() == 0); + if (!privileged) + ksft_test_result_skip("privileged tests require euid == 0\n"); + else { + test_reopen_ordinary(privileged); + + E_setresuid(65534, 65534, 65534); + privileged = (geteuid() == 0); + } + + test_reopen_ordinary(privileged); + test_openat2_cloexec_test(); + + if (ksft_get_fail_cnt() + ksft_get_error_cnt() > 0) + ksft_exit_fail(); + else + ksft_exit_pass(); +} diff --git a/tools/testing/selftests/openat2/rename_attack_test.c b/tools/testing/selftests/openat2/rename_attack_test.c new file mode 100644 index 000000000000..39b20ea185d5 --- /dev/null +++ b/tools/testing/selftests/openat2/rename_attack_test.c @@ -0,0 +1,127 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * Author: Aleksa Sarai cyphar@cyphar.com + * Copyright (C) 2018-2019 SUSE LLC. + */ + +#define _GNU_SOURCE +#include <errno.h> +#include <fcntl.h> +#include <sched.h> +#include <sys/stat.h> +#include <sys/types.h> +#include <sys/mount.h> +#include <sys/mman.h> +#include <sys/prctl.h> +#include <signal.h> +#include <stdio.h> +#include <stdlib.h> +#include <stdbool.h> +#include <string.h> +#include <syscall.h> +#include <limits.h> +#include <unistd.h> + +#include "../kselftest.h" +#include "helpers.h" + +/* Construct a test directory with the following structure: + * + * root/ + * |-- a/ + * | `-- c/ + * `-- b/ + */ +int setup_testdir(void) +{ + int dfd; + char dirname[] = "/tmp/ksft-openat2-rename-attack.XXXXXX"; + + /* Make the top-level directory. */ + if (!mkdtemp(dirname)) + ksft_exit_fail_msg("setup_testdir: failed to create tmpdir\n"); + dfd = open(dirname, O_PATH | O_DIRECTORY); + if (dfd < 0) + ksft_exit_fail_msg("setup_testdir: failed to open tmpdir\n"); + + E_mkdirat(dfd, "a", 0755); + E_mkdirat(dfd, "b", 0755); + E_mkdirat(dfd, "a/c", 0755); + + return dfd; +} + +/* Swap @dirfd/@a and @dirfd/@b constantly. Parent must kill this process. */ +pid_t spawn_attack(int dirfd, char *a, char *b) +{ + pid_t child = fork(); + if (child != 0) + return child; + + /* If the parent (the test process) dies, kill ourselves too. */ + prctl(PR_SET_PDEATHSIG, SIGKILL); + + /* Swap @a and @b. */ + for (;;) + renameat2(dirfd, a, dirfd, b, RENAME_EXCHANGE); + exit(1); +} + +#define NUM_RENAME_TESTS 1 +#define ROUNDS 400000 + +void test_rename_attack(void) +{ + int dfd, afd, escaped_count = 0; + void (*resultfn)(const char *msg, ...) = ksft_test_result_pass; + pid_t child; + + dfd = setup_testdir(); + afd = openat(dfd, "a", O_PATH); + if (afd < 0) + ksft_exit_fail_msg("test_rename_attack: failed to open 'a'\n"); + + child = spawn_attack(dfd, "a/c", "b"); + + for (int i = 0; i < ROUNDS; i++) { + int fd; + bool failed; + struct open_how how = { + .flags = O_PATH, + .resolve = RESOLVE_IN_ROOT, + }; + char *victim_path = "c/../../c/../../c/../../c/../../c/../../c/../../c/../../c/../../c/../../c/../../c/../../c/../../c/../../c/../../c/../../c/../../c/../../c/../../c/../.."; + + fd = sys_openat2(afd, victim_path, &how); + if (fd < 0) + failed = (fd != -EXDEV); + else + failed = !fdequal(fd, afd, NULL); + + escaped_count += failed; + close(fd); + } + + if (escaped_count > 0) + resultfn = ksft_test_result_fail; + + resultfn("rename attack fails (expected 0 breakouts in %d runs, got %d)\n", + ROUNDS, escaped_count); + + /* Should be killed anyway, but might as well make sure. */ + kill(child, SIGKILL); +} + +int main(int argc, char **argv) +{ + ksft_print_header(); + ksft_set_plan(NUM_RENAME_TESTS); + test_openat2_supported(); + + test_rename_attack(); + + if (ksft_get_fail_cnt() + ksft_get_error_cnt() > 0) + ksft_exit_fail(); + else + ksft_exit_pass(); +} diff --git a/tools/testing/selftests/openat2/resolve_test.c b/tools/testing/selftests/openat2/resolve_test.c new file mode 100644 index 000000000000..8ef3dbb7edbe --- /dev/null +++ b/tools/testing/selftests/openat2/resolve_test.c @@ -0,0 +1,402 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * Author: Aleksa Sarai cyphar@cyphar.com + * Copyright (C) 2018-2019 SUSE LLC. + */ + +#define _GNU_SOURCE +#include <fcntl.h> +#include <sched.h> +#include <sys/stat.h> +#include <sys/types.h> +#include <sys/mount.h> +#include <stdlib.h> +#include <stdbool.h> +#include <string.h> + +#include "../kselftest.h" +#include "helpers.h" + +/* + * Construct a test directory with the following structure: + * + * root/ + * |-- procexe -> /proc/self/exe + * |-- procroot -> /proc/self/root + * |-- root/ + * |-- mnt/ [mountpoint] + * | |-- self -> ../mnt/ + * | `-- absself -> /mnt/ + * |-- etc/ + * | `-- passwd + * |-- creatlink -> /newfile3 + * |-- relsym -> etc/passwd + * |-- abssym -> /etc/passwd + * |-- abscheeky -> /cheeky + * |-- abscheeky -> /cheeky + * `-- cheeky/ + * |-- absself -> / + * |-- self -> ../../root/ + * |-- garbageself -> /../../root/ + * |-- passwd -> ../cheeky/../cheeky/../etc/../etc/passwd + * |-- abspasswd -> /../cheeky/../cheeky/../etc/../etc/passwd + * |-- dotdotlink -> ../../../../../../../../../../../../../../etc/passwd + * `-- garbagelink -> /../../../../../../../../../../../../../../etc/passwd + */ +int setup_testdir(void) +{ + int dfd, tmpfd; + char dirname[] = "/tmp/ksft-openat2-testdir.XXXXXX"; + + /* Unshare and make /tmp a new directory. */ + E_unshare(CLONE_NEWNS); + E_mount("", "/tmp", "", MS_PRIVATE, ""); + + /* Make the top-level directory. */ + if (!mkdtemp(dirname)) + ksft_exit_fail_msg("setup_testdir: failed to create tmpdir\n"); + dfd = open(dirname, O_PATH | O_DIRECTORY); + if (dfd < 0) + ksft_exit_fail_msg("setup_testdir: failed to open tmpdir\n"); + + /* A sub-directory which is actually used for tests. */ + E_mkdirat(dfd, "root", 0755); + tmpfd = openat(dfd, "root", O_PATH | O_DIRECTORY); + if (tmpfd < 0) + ksft_exit_fail_msg("setup_testdir: failed to open tmpdir\n"); + close(dfd); + dfd = tmpfd; + + E_symlinkat("/proc/self/exe", dfd, "procexe"); + E_symlinkat("/proc/self/root", dfd, "procroot"); + E_mkdirat(dfd, "root", 0755); + + /* There is no mountat(2), so use chdir. */ + E_mkdirat(dfd, "mnt", 0755); + E_fchdir(dfd); + E_mount("tmpfs", "./mnt", "tmpfs", MS_NOSUID | MS_NODEV, ""); + E_symlinkat("../mnt/", dfd, "mnt/self"); + E_symlinkat("/mnt/", dfd, "mnt/absself"); + + E_mkdirat(dfd, "etc", 0755); + E_touchat(dfd, "etc/passwd"); + + E_symlinkat("/newfile3", dfd, "creatlink"); + E_symlinkat("etc/passwd", dfd, "relsym"); + E_symlinkat("/etc/passwd", dfd, "abssym"); + E_symlinkat("/cheeky", dfd, "abscheeky"); + + E_mkdirat(dfd, "cheeky", 0755); + + E_symlinkat("/", dfd, "cheeky/absself"); + E_symlinkat("../../root/", dfd, "cheeky/self"); + E_symlinkat("/../../root/", dfd, "cheeky/garbageself"); + + E_symlinkat("../cheeky/../etc/../etc/passwd", dfd, "cheeky/passwd"); + E_symlinkat("/../cheeky/../etc/../etc/passwd", dfd, "cheeky/abspasswd"); + + E_symlinkat("../../../../../../../../../../../../../../etc/passwd", + dfd, "cheeky/dotdotlink"); + E_symlinkat("/../../../../../../../../../../../../../../etc/passwd", + dfd, "cheeky/garbagelink"); + + return dfd; +} + +struct basic_test { + const char *dir; + const char *path; + struct open_how how; + bool pass; + union { + int err; + const char *path; + } out; +}; + +#define NUM_OPENAT2_OPATH_TESTS 84 + +void test_openat2_opath_tests(void) +{ + int rootfd; + char *procselfexe; + + E_asprintf(&procselfexe, "/proc/%d/exe", getpid()); + rootfd = setup_testdir(); + + struct basic_test tests[] = { + /** RESOLVE_BENEATH **/ + /* Attempts to cross dirfd should be blocked. */ + { .path = "/", .how.resolve = RESOLVE_BENEATH, + .out.err = -EXDEV, .pass = false }, + { .path = "cheeky/absself", .how.resolve = RESOLVE_BENEATH, + .out.err = -EXDEV, .pass = false }, + { .path = "abscheeky/absself", .how.resolve = RESOLVE_BENEATH, + .out.err = -EXDEV, .pass = false }, + { .path = "..", .how.resolve = RESOLVE_BENEATH, + .out.err = -EXDEV, .pass = false }, + { .path = "../root/", .how.resolve = RESOLVE_BENEATH, + .out.err = -EXDEV, .pass = false }, + { .path = "cheeky/self", .how.resolve = RESOLVE_BENEATH, + .out.err = -EXDEV, .pass = false }, + { .path = "abscheeky/self", .how.resolve = RESOLVE_BENEATH, + .out.err = -EXDEV, .pass = false }, + { .path = "cheeky/garbageself", .how.resolve = RESOLVE_BENEATH, + .out.err = -EXDEV, .pass = false }, + { .path = "abscheeky/garbageself", .how.resolve = RESOLVE_BENEATH, + .out.err = -EXDEV, .pass = false }, + /* Only relative paths that stay inside dirfd should work. */ + { .path = "root", .how.resolve = RESOLVE_BENEATH, + .out.path = "root", .pass = true }, + { .path = "etc", .how.resolve = RESOLVE_BENEATH, + .out.path = "etc", .pass = true }, + { .path = "etc/passwd", .how.resolve = RESOLVE_BENEATH, + .out.path = "etc/passwd", .pass = true }, + { .path = "relsym", .how.resolve = RESOLVE_BENEATH, + .out.path = "etc/passwd", .pass = true }, + { .path = "cheeky/passwd", .how.resolve = RESOLVE_BENEATH, + .out.path = "etc/passwd", .pass = true }, + { .path = "abscheeky/passwd", .how.resolve = RESOLVE_BENEATH, + .out.err = -EXDEV, .pass = false }, + { .path = "abssym", .how.resolve = RESOLVE_BENEATH, + .out.err = -EXDEV, .pass = false }, + { .path = "/etc/passwd", .how.resolve = RESOLVE_BENEATH, + .out.err = -EXDEV, .pass = false }, + { .path = "cheeky/abspasswd", .how.resolve = RESOLVE_BENEATH, + .out.err = -EXDEV, .pass = false }, + { .path = "abscheeky/abspasswd", .how.resolve = RESOLVE_BENEATH, + .out.err = -EXDEV, .pass = false }, + /* Tricky paths should fail. */ + { .path = "cheeky/dotdotlink", .how.resolve = RESOLVE_BENEATH, + .out.err = -EXDEV, .pass = false }, + { .path = "abscheeky/dotdotlink", .how.resolve = RESOLVE_BENEATH, + .out.err = -EXDEV, .pass = false }, + { .path = "cheeky/garbagelink", .how.resolve = RESOLVE_BENEATH, + .out.err = -EXDEV, .pass = false }, + { .path = "abscheeky/garbagelink", .how.resolve = RESOLVE_BENEATH, + .out.err = -EXDEV, .pass = false }, + + /** RESOLVE_IN_ROOT **/ + /* All attempts to cross the dirfd will be scoped-to-root. */ + { .path = "/", .how.resolve = RESOLVE_IN_ROOT, + .out.path = NULL, .pass = true }, + { .path = "cheeky/absself", .how.resolve = RESOLVE_IN_ROOT, + .out.path = NULL, .pass = true }, + { .path = "abscheeky/absself", .how.resolve = RESOLVE_IN_ROOT, + .out.path = NULL, .pass = true }, + { .path = "..", .how.resolve = RESOLVE_IN_ROOT, + .out.path = NULL, .pass = true }, + { .path = "../root/", .how.resolve = RESOLVE_IN_ROOT, + .out.path = "root", .pass = true }, + { .path = "../root/", .how.resolve = RESOLVE_IN_ROOT, + .out.path = "root", .pass = true }, + { .path = "cheeky/self", .how.resolve = RESOLVE_IN_ROOT, + .out.path = "root", .pass = true }, + { .path = "cheeky/garbageself", .how.resolve = RESOLVE_IN_ROOT, + .out.path = "root", .pass = true }, + { .path = "abscheeky/garbageself", .how.resolve = RESOLVE_IN_ROOT, + .out.path = "root", .pass = true }, + { .path = "root", .how.resolve = RESOLVE_IN_ROOT, + .out.path = "root", .pass = true }, + { .path = "etc", .how.resolve = RESOLVE_IN_ROOT, + .out.path = "etc", .pass = true }, + { .path = "etc/passwd", .how.resolve = RESOLVE_IN_ROOT, + .out.path = "etc/passwd", .pass = true }, + { .path = "relsym", .how.resolve = RESOLVE_IN_ROOT, + .out.path = "etc/passwd", .pass = true }, + { .path = "cheeky/passwd", .how.resolve = RESOLVE_IN_ROOT, + .out.path = "etc/passwd", .pass = true }, + { .path = "abscheeky/passwd", .how.resolve = RESOLVE_IN_ROOT, + .out.path = "etc/passwd", .pass = true }, + { .path = "abssym", .how.resolve = RESOLVE_IN_ROOT, + .out.path = "etc/passwd", .pass = true }, + { .path = "/etc/passwd", .how.resolve = RESOLVE_IN_ROOT, + .out.path = "etc/passwd", .pass = true }, + { .path = "cheeky/abspasswd", .how.resolve = RESOLVE_IN_ROOT, + .out.path = "etc/passwd", .pass = true }, + { .path = "abscheeky/abspasswd", .how.resolve = RESOLVE_IN_ROOT, + .out.path = "etc/passwd", .pass = true }, + { .path = "cheeky/dotdotlink", .how.resolve = RESOLVE_IN_ROOT, + .out.path = "etc/passwd", .pass = true }, + { .path = "abscheeky/dotdotlink", .how.resolve = RESOLVE_IN_ROOT, + .out.path = "etc/passwd", .pass = true }, + { .path = "/../../../../abscheeky/dotdotlink", .how.resolve = RESOLVE_IN_ROOT, + .out.path = "etc/passwd", .pass = true }, + { .path = "cheeky/garbagelink", .how.resolve = RESOLVE_IN_ROOT, + .out.path = "etc/passwd", .pass = true }, + { .path = "abscheeky/garbagelink", .how.resolve = RESOLVE_IN_ROOT, + .out.path = "etc/passwd", .pass = true }, + { .path = "/../../../../abscheeky/garbagelink", .how.resolve = RESOLVE_IN_ROOT, + .out.path = "etc/passwd", .pass = true }, + /* O_CREAT should handle trailing symlinks correctly. */ + { .path = "newfile1", .how.flags = O_CREAT, + .how.mode = 0700, + .how.resolve = RESOLVE_IN_ROOT, + .out.path = "newfile1", .pass = true }, + { .path = "/newfile2", .how.flags = O_CREAT, + .how.mode = 0700, + .how.resolve = RESOLVE_IN_ROOT, + .out.path = "newfile2", .pass = true }, + { .path = "/creatlink", .how.flags = O_CREAT, + .how.mode = 0700, + .how.resolve = RESOLVE_IN_ROOT, + .out.path = "newfile3", .pass = true }, + + /** RESOLVE_NO_XDEV **/ + /* Crossing *down* into a mountpoint is disallowed. */ + { .path = "mnt", .how.resolve = RESOLVE_NO_XDEV, + .out.err = -EXDEV, .pass = false }, + { .path = "mnt/", .how.resolve = RESOLVE_NO_XDEV, + .out.err = -EXDEV, .pass = false }, + { .path = "mnt/.", .how.resolve = RESOLVE_NO_XDEV, + .out.err = -EXDEV, .pass = false }, + /* Crossing *up* out of a mountpoint is disallowed. */ + { .dir = "mnt", .path = ".", .how.resolve = RESOLVE_NO_XDEV, + .out.path = "mnt", .pass = true }, + { .dir = "mnt", .path = "..", .how.resolve = RESOLVE_NO_XDEV, + .out.err = -EXDEV, .pass = false }, + { .dir = "mnt", .path = "../mnt", .how.resolve = RESOLVE_NO_XDEV, + .out.err = -EXDEV, .pass = false }, + { .dir = "mnt", .path = "self", .how.resolve = RESOLVE_NO_XDEV, + .out.err = -EXDEV, .pass = false }, + { .dir = "mnt", .path = "absself", .how.resolve = RESOLVE_NO_XDEV, + .out.err = -EXDEV, .pass = false }, + /* Jumping to "/" is ok, but later components cannot cross. */ + { .dir = "mnt", .path = "/", .how.resolve = RESOLVE_NO_XDEV, + .out.path = "/", .pass = true }, + { .dir = "/", .path = "/", .how.resolve = RESOLVE_NO_XDEV, + .out.path = "/", .pass = true }, + { .path = "/proc/1", .how.resolve = RESOLVE_NO_XDEV, + .out.err = -EXDEV, .pass = false }, + { .path = "/tmp", .how.resolve = RESOLVE_NO_XDEV, + .out.err = -EXDEV, .pass = false }, + + /** RESOLVE_NO_MAGICLINKS **/ + /* Regular symlinks should work. */ + { .path = "relsym", .how.resolve = RESOLVE_NO_MAGICLINKS, + .out.path = "etc/passwd", .pass = true }, + /* Magic-links should not work. */ + { .path = "procexe", .how.resolve = RESOLVE_NO_MAGICLINKS, + .out.err = -ELOOP, .pass = false }, + { .path = "/proc/self/exe", .how.resolve = RESOLVE_NO_MAGICLINKS, + .out.err = -ELOOP, .pass = false }, + { .path = "procroot/etc", .how.resolve = RESOLVE_NO_MAGICLINKS, + .out.err = -ELOOP, .pass = false }, + { .path = "/proc/self/root/etc", .how.resolve = RESOLVE_NO_MAGICLINKS, + .out.err = -ELOOP, .pass = false }, + { .path = "/proc/self/root/etc", .how.flags = O_NOFOLLOW, + .how.resolve = RESOLVE_NO_MAGICLINKS, + .out.err = -ELOOP, .pass = false }, + { .path = "/proc/self/exe", .how.flags = O_NOFOLLOW, + .how.resolve = RESOLVE_NO_MAGICLINKS, + .out.path = procselfexe, .pass = true }, + + /** RESOLVE_NO_SYMLINKS **/ + /* Normal paths should work. */ + { .path = ".", .how.resolve = RESOLVE_NO_SYMLINKS, + .out.path = NULL, .pass = true }, + { .path = "root", .how.resolve = RESOLVE_NO_SYMLINKS, + .out.path = "root", .pass = true }, + { .path = "etc", .how.resolve = RESOLVE_NO_SYMLINKS, + .out.path = "etc", .pass = true }, + { .path = "etc/passwd", .how.resolve = RESOLVE_NO_SYMLINKS, + .out.path = "etc/passwd", .pass = true }, + /* Regular symlinks are blocked. */ + { .path = "relsym", .how.resolve = RESOLVE_NO_SYMLINKS, + .out.err = -ELOOP, .pass = false }, + { .path = "abssym", .how.resolve = RESOLVE_NO_SYMLINKS, + .out.err = -ELOOP, .pass = false }, + { .path = "cheeky/garbagelink", .how.resolve = RESOLVE_NO_SYMLINKS, + .out.err = -ELOOP, .pass = false }, + { .path = "abscheeky/garbagelink", .how.resolve = RESOLVE_NO_SYMLINKS, + .out.err = -ELOOP, .pass = false }, + { .path = "abscheeky/absself", .how.resolve = RESOLVE_NO_SYMLINKS, + .out.err = -ELOOP, .pass = false }, + /* Trailing symlinks with NO_FOLLOW. */ + { .path = "relsym", .how.flags = O_NOFOLLOW, + .how.resolve = RESOLVE_NO_SYMLINKS, + .out.path = "relsym", .pass = true }, + { .path = "abssym", .how.flags = O_NOFOLLOW, + .how.resolve = RESOLVE_NO_SYMLINKS, + .out.path = "abssym", .pass = true }, + { .path = "cheeky/garbagelink", .how.flags = O_NOFOLLOW, + .how.resolve = RESOLVE_NO_SYMLINKS, + .out.path = "cheeky/garbagelink", .pass = true }, + { .path = "abscheeky/garbagelink", .how.flags = O_NOFOLLOW, + .how.resolve = RESOLVE_NO_SYMLINKS, + .out.err = -ELOOP, .pass = false }, + { .path = "abscheeky/absself", .how.flags = O_NOFOLLOW, + .how.resolve = RESOLVE_NO_SYMLINKS, + .out.err = -ELOOP, .pass = false }, + }; + + BUILD_BUG_ON(ARRAY_LEN(tests) != NUM_OPENAT2_OPATH_TESTS); + + for (int i = 0; i < ARRAY_LEN(tests); i++) { + int dfd, fd; + bool failed; + void (*resultfn)(const char *msg, ...) = ksft_test_result_pass; + struct basic_test *test = &tests[i]; + char *flagstr; + + /* Auto-set O_PATH. */ + if (!(test->how.flags & O_CREAT)) + test->how.flags |= O_PATH; + flagstr = openat2_flags(&test->how); + + if (test->dir) + dfd = openat(rootfd, test->dir, O_PATH | O_DIRECTORY); + else + dfd = dup(rootfd); + if (dfd < 0) { + resultfn = ksft_test_result_error; + goto next; + } + + fd = sys_openat2(dfd, test->path, &test->how); + if (test->pass) + failed = (fd < 0 || !fdequal(fd, rootfd, test->out.path)); + else + failed = (fd != test->out.err); + if (fd >= 0) + close(fd); + close(dfd); + + if (failed) + resultfn = ksft_test_result_fail; + +next: + if (test->pass) + resultfn("openat2(root[%s], %s, %s) ==> %s\n", + test->dir ?: ".", test->path, flagstr, + test->out.path ?: "."); + else + resultfn("openat2(root[%s], %s, %s) ==> %d (%s)\n", + test->dir ?: ".", test->path, flagstr, + test->out.err, strerror(-test->out.err)); + fflush(stdout); + + free(flagstr); + } + + free(procselfexe); + close(rootfd); +} + +int main(int argc, char **argv) +{ + ksft_print_header(); + ksft_set_plan(NUM_OPENAT2_OPATH_TESTS); + test_openat2_supported(); + + /* NOTE: We should be checking for CAP_SYS_ADMIN here... */ + if (geteuid() != 0) + ksft_exit_skip("openat2(2) tests require euid == 0\n"); + + test_openat2_opath_tests(); + + if (ksft_get_fail_cnt() + ksft_get_error_cnt() > 0) + ksft_exit_fail(); + else + ksft_exit_pass(); +}
linux-kselftest-mirror@lists.linaro.org
-
Aleksa Sarai -
Daniel Colascione -
Rasmus Villemoes