/* Background. */ For a very long time, extending openat(2) with new features has been incredibly frustrating. This stems from the fact that openat(2) is possibly the most famous counter-example to the mantra "don't silently accept garbage from userspace" -- it doesn't check whether unknown flags are present[1].
This means that (generally) the addition of new flags to openat(2) has been fraught with backwards-compatibility issues (O_TMPFILE has to be defined as __O_TMPFILE|O_DIRECTORY|[O_RDWR or O_WRONLY] to ensure old kernels gave errors, since it's insecure to silently ignore the flag[2]). All new security-related flags therefore have a tough road to being added to openat(2).
Userspace also has a hard time figuring out whether a particular flag is supported on a particular kernel. While it is now possible with contemporary kernels (thanks to [3]), older kernels will expose unknown flag bits through fcntl(F_GETFL). Giving a clear -EINVAL during openat(2) time matches modern syscall designs and is far more fool-proof.
In addition, the newly-added path resolution restriction LOOKUP flags (which we would like to expose to user-space) don't feel related to the pre-existing O_* flag set -- they affect all components of path lookup. We'd therefore like to add a new flag argument.
Adding a new syscall allows us to finally fix the flag-ignoring problem, and we can make it extensible enough so that we will hopefully never need an openat3(2).
/* Syscall Prototype. */ /* * open_how is an extensible structure (similar in interface to * clone3(2) or sched_setattr(2)). The size parameter must be set to * sizeof(struct open_how), to allow for future extensions. All future * extensions will be appended to open_how, with their zero value * acting as a no-op default. */ struct open_how { /* ... */ };
int openat2(int dfd, const char *pathname, struct open_how *how, size_t size);
/* Description. */ The initial version of 'struct open_how' contains the following fields:
flags Used to specify openat(2)-style flags. However, any unknown flag bits or otherwise incorrect flag combinations (like O_PATH|O_RDWR) will result in -EINVAL. In addition, this field is 64-bits wide to allow for more O_ flags than currently permitted with openat(2).
mode The file mode for O_CREAT or O_TMPFILE.
Must be set to zero if flags does not contain O_CREAT or O_TMPFILE.
resolve Restrict path resolution (in contrast to O_* flags they affect all path components). The current set of flags are as follows (at the moment, all of the RESOLVE_ flags are implemented as just passing the corresponding LOOKUP_ flag).
RESOLVE_NO_XDEV => LOOKUP_NO_XDEV RESOLVE_NO_SYMLINKS => LOOKUP_NO_SYMLINKS RESOLVE_NO_MAGICLINKS => LOOKUP_NO_MAGICLINKS RESOLVE_BENEATH => LOOKUP_BENEATH RESOLVE_IN_ROOT => LOOKUP_IN_ROOT
open_how does not contain an embedded size field, because it is of little benefit (userspace can figure out the kernel open_how size at runtime fairly easily without it). It also only contains u64s (even though ->mode arguably should be a u16) to avoid having padding fields which are never used in the future.
Note that as a result of the new how->flags handling, O_PATH|O_TMPFILE is no longer permitted for openat(2). As far as I can tell, this has always been a bug and appears to not be used by userspace (and I've not seen any problems on my machines by disallowing it). If it turns out this breaks something, we can special-case it and only permit it for openat(2) but not openat2(2).
After input from Florian Weimer, the new open_how and flag definitions are inside a separate header from uapi/linux/fcntl.h, to avoid problems that glibc has with importing that header.
/* Testing. */ In a follow-up patch there are over 200 selftests which ensure that this syscall has the correct semantics and will correctly handle several attack scenarios.
In addition, I've written a userspace library[4] which provides convenient wrappers around openat2(RESOLVE_IN_ROOT) (this is necessary because no other syscalls support RESOLVE_IN_ROOT, and thus lots of care must be taken when using RESOLVE_IN_ROOT'd file descriptors with other syscalls). During the development of this patch, I've run numerous verification tests using libpathrs (showing that the API is reasonably usable by userspace).
/* Future Work. */ Additional RESOLVE_ flags have been suggested during the review period. These can be easily implemented separately (such as blocking auto-mount during resolution).
Furthermore, there are some other proposed changes to the openat(2) interface (the most obvious example is magic-link hardening[5]) which would be a good opportunity to add a way for userspace to restrict how O_PATH file descriptors can be re-opened.
Another possible avenue of future work would be some kind of CHECK_FIELDS[6] flag which causes the kernel to indicate to userspace which openat2(2) flags and fields are supported by the current kernel (to avoid userspace having to go through several guesses to figure it out).
[1]: https://lwn.net/Articles/588444/ [2]: https://lore.kernel.org/lkml/CA+55aFyyxJL1LyXZeBsf2ypriraj5ut1XkNDsunRBqgVjZ... [3]: commit 629e014bb834 ("fs: completely ignore unknown open flags") [4]: https://sourceware.org/bugzilla/show_bug.cgi?id=17523 [5]: https://lore.kernel.org/lkml/20190930183316.10190-2-cyphar@cyphar.com/ [6]: https://youtu.be/ggD-eb3yPVs
Suggested-by: Christian Brauner christian.brauner@ubuntu.com Signed-off-by: Aleksa Sarai cyphar@cyphar.com Signed-off-by: Al Viro viro@zeniv.linux.org.uk --- CREDITS | 4 +- MAINTAINERS | 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/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 | 147 +++++++++++++++----- include/linux/fcntl.h | 16 ++- include/linux/syscalls.h | 3 + include/uapi/asm-generic/unistd.h | 5 +- include/uapi/linux/fcntl.h | 2 +- include/uapi/linux/openat2.h | 39 ++++++ 26 files changed, 198 insertions(+), 39 deletions(-) create mode 100644 include/uapi/linux/openat2.h
diff --git a/CREDITS b/CREDITS index 9602b0fa1c95..a97d3280a627 100644 --- a/CREDITS +++ b/CREDITS @@ -3302,7 +3302,9 @@ S: France N: Aleksa Sarai E: cyphar@cyphar.com W: https://www.cyphar.com/ -D: `pids` cgroup subsystem +D: /sys/fs/cgroup/pids +D: openat2(2) +S: Sydney, Australia
N: Dipankar Sarma E: dipankar@in.ibm.com diff --git a/MAINTAINERS b/MAINTAINERS index bd5847e802de..737ada377ac3 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -6397,6 +6397,7 @@ F: fs/* F: include/linux/fs.h F: include/linux/fs_types.h F: include/uapi/linux/fs.h +F: include/uapi/linux/openat2.h
FINTEK F75375S HARDWARE MONITOR AND FAN CONTROLLER DRIVER M: Riku Voipio riku.voipio@iki.fi diff --git a/arch/alpha/kernel/syscalls/syscall.tbl b/arch/alpha/kernel/syscalls/syscall.tbl index 8e13b0b2928d..4d7f2ffa957c 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 e7c5ab38e403..68c9ec06851f 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 n32 clone3 __sys_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 13cd66581f3b..42a72d010050 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 n64 clone3 __sys_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 353539ea4140..f114c4aed0ed 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 o32 clone3 __sys_clone3 +437 o32 openat2 sys_openat2 diff --git a/arch/parisc/kernel/syscalls/syscall.tbl b/arch/parisc/kernel/syscalls/syscall.tbl index 285ff516150c..b550ae9a7fea 100644 --- a/arch/parisc/kernel/syscalls/syscall.tbl +++ b/arch/parisc/kernel/syscalls/syscall.tbl @@ -433,3 +433,4 @@ 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 15908eb9b17e..d22a8b5c3fab 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 b62f5c0923a8..8cdb2b675867 100644 --- a/fs/open.c +++ b/fs/open.c @@ -955,48 +955,84 @@ 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) +#define WILL_CREATE(flags) (flags & (O_CREAT | __O_TMPFILE)) +#define O_PATH_FLAGS (O_DIRECTORY | O_NOFOLLOW | O_PATH | O_CLOEXEC) + +static inline struct open_how build_open_how(int flags, umode_t mode) +{ + struct open_how how = { + .flags = flags & VALID_OPEN_FLAGS, + .mode = mode & S_IALLUGO, + }; + + /* O_PATH beats everything else. */ + if (how.flags & O_PATH) + how.flags &= O_PATH_FLAGS; + /* Modes should only be set for create-like flags. */ + if (!WILL_CREATE(how.flags)) + how.mode = 0; + return how; +} + +static inline int build_open_flags(const struct open_how *how, + struct open_flags *op) { + int flags = how->flags; int lookup_flags = 0; int acc_mode = ACC_MODE(flags);
+ /* Must never be set by userspace */ + flags &= ~(FMODE_NONOTIFY | O_CLOEXEC); + /* - * 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 implicitly clear all of the invalid flags or argument + * values before calling build_open_flags(), but openat2(2) checks all + * of its arguments. */ - flags &= VALID_OPEN_FLAGS; + if (flags & ~VALID_OPEN_FLAGS) + return -EINVAL; + if (how->resolve & ~VALID_RESOLVE_FLAGS) + return -EINVAL;
- if (flags & (O_CREAT | __O_TMPFILE)) - op->mode = (mode & S_IALLUGO) | S_IFREG; - else + /* Deal with the mode. */ + if (WILL_CREATE(flags)) { + if (how->mode & ~S_IALLUGO) + return -EINVAL; + op->mode = how->mode | S_IFREG; + } else { + if (how->mode != 0) + return -EINVAL; op->mode = 0; - - /* Must never be set by userspace */ - flags &= ~FMODE_NONOTIFY & ~O_CLOEXEC; + }
/* - * O_SYNC is implemented as __O_SYNC|O_DSYNC. As many places only - * check for O_DSYNC if the need any syncing at all we enforce it's - * always set instead of having to deal with possibly weird behaviour - * for malicious applications setting only __O_SYNC. + * In order to ensure programs get explicit errors when trying to use + * O_TMPFILE on old kernels, O_TMPFILE is implemented such that it + * looks like (O_DIRECTORY|O_RDWR & ~O_CREAT) to old kernels. But we + * have to require userspace to explicitly set it. */ - if (flags & __O_SYNC) - flags |= O_DSYNC; - if (flags & __O_TMPFILE) { if ((flags & O_TMPFILE_MASK) != O_TMPFILE) return -EINVAL; if (!(acc_mode & MAY_WRITE)) return -EINVAL; - } else if (flags & O_PATH) { - /* - * If we have O_PATH in the open flag. Then we - * cannot have anything other than the below set of flags - */ - flags &= O_DIRECTORY | O_NOFOLLOW | O_PATH; + } + if (flags & O_PATH) { + /* O_PATH only permits certain other flags to be set. */ + if (flags & ~O_PATH_FLAGS) + return -EINVAL; acc_mode = 0; }
+ /* + * O_SYNC is implemented as __O_SYNC|O_DSYNC. As many places only + * check for O_DSYNC if the need any syncing at all we enforce it's + * always set instead of having to deal with possibly weird behaviour + * for malicious applications setting only __O_SYNC. + */ + if (flags & __O_SYNC) + flags |= O_DSYNC; + op->open_flag = flags;
/* O_TRUNC implies we need access checks for write permissions */ @@ -1022,6 +1058,18 @@ 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 (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; } @@ -1040,8 +1088,11 @@ 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 = build_open_how(flags, mode); + int err = build_open_flags(&how, &op); + if (err) + return ERR_PTR(err); + return do_filp_open(AT_FDCWD, name, &op); }
/** @@ -1072,17 +1123,19 @@ 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 = build_open_how(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) +static long do_sys_openat2(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); struct filename *tmp;
if (fd) @@ -1092,7 +1145,7 @@ long do_sys_open(int dfd, const char __user *filename, int flags, umode_t mode) if (IS_ERR(tmp)) return PTR_ERR(tmp);
- 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)) { @@ -1107,12 +1160,16 @@ long do_sys_open(int dfd, const char __user *filename, int flags, umode_t mode) return fd; }
-SYSCALL_DEFINE3(open, const char __user *, filename, int, flags, umode_t, mode) +long do_sys_open(int dfd, const char __user *filename, int flags, umode_t mode) { - if (force_o_largefile()) - flags |= O_LARGEFILE; + struct open_how how = build_open_how(flags, mode); + return do_sys_openat2(dfd, filename, &how); +}
- return do_sys_open(AT_FDCWD, filename, flags, mode); + +SYSCALL_DEFINE3(open, const char __user *, filename, int, flags, umode_t, mode) +{ + return ksys_open(filename, flags, mode); }
SYSCALL_DEFINE4(openat, int, dfd, const char __user *, filename, int, flags, @@ -1120,10 +1177,32 @@ SYSCALL_DEFINE4(openat, int, dfd, const char __user *, filename, int, flags, { if (force_o_largefile()) flags |= O_LARGEFILE; - return do_sys_open(dfd, filename, flags, mode); }
+SYSCALL_DEFINE4(openat2, int, dfd, const char __user *, filename, + struct open_how __user *, how, size_t, usize) +{ + int err; + struct open_how tmp; + + BUILD_BUG_ON(sizeof(struct open_how) < OPEN_HOW_SIZE_VER0); + BUILD_BUG_ON(sizeof(struct open_how) != OPEN_HOW_SIZE_LATEST); + + if (unlikely(usize < OPEN_HOW_SIZE_VER0)) + return -EINVAL; + + err = copy_struct_from_user(&tmp, sizeof(tmp), how, usize); + if (err) + return err; + + /* O_LARGEFILE is only allowed for non-O_PATH. */ + if (!(tmp.flags & O_PATH) && force_o_largefile()) + tmp.flags |= O_LARGEFILE; + + return do_sys_openat2(dfd, filename, &tmp); +} + #ifdef CONFIG_COMPAT /* * Exactly like sys_open(), except that it doesn't set the diff --git a/include/linux/fcntl.h b/include/linux/fcntl.h index d019df946cb2..7bcdcf4f6ab2 100644 --- a/include/linux/fcntl.h +++ b/include/linux/fcntl.h @@ -2,15 +2,29 @@ #ifndef _LINUX_FCNTL_H #define _LINUX_FCNTL_H
+#include <linux/stat.h> #include <uapi/linux/fcntl.h>
-/* list of all valid flags for the open/openat flags argument: */ +/* 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)
+/* 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) + +/* List of all open_how "versions". */ +#define OPEN_HOW_SIZE_VER0 24 /* sizeof first published struct */ +#define OPEN_HOW_SIZE_LATEST OPEN_HOW_SIZE_VER0 + #ifndef force_o_largefile #define force_o_largefile() (!IS_ENABLED(CONFIG_ARCH_32BIT_OFF_T)) #endif diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h index d0391cc2dae9..cd9f27cbc567 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, + struct open_how *how, size_t size); asmlinkage long sys_close(unsigned int fd); asmlinkage long sys_vhangup(void);
diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h index 1fc8faa6e973..d4122c091472 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 1f97b33c840e..ca88b7bce553 100644 --- a/include/uapi/linux/fcntl.h +++ b/include/uapi/linux/fcntl.h @@ -3,6 +3,7 @@ #define _UAPI_LINUX_FCNTL_H
#include <asm/fcntl.h> +#include <linux/openat2.h>
#define F_SETLEASE (F_LINUX_SPECIFIC_BASE + 0) #define F_GETLEASE (F_LINUX_SPECIFIC_BASE + 1) @@ -100,5 +101,4 @@
#define AT_RECURSIVE 0x8000 /* Apply to the entire subtree */
- #endif /* _UAPI_LINUX_FCNTL_H */ diff --git a/include/uapi/linux/openat2.h b/include/uapi/linux/openat2.h new file mode 100644 index 000000000000..58b1eb711360 --- /dev/null +++ b/include/uapi/linux/openat2.h @@ -0,0 +1,39 @@ +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */ +#ifndef _UAPI_LINUX_OPENAT2_H +#define _UAPI_LINUX_OPENAT2_H + +#include <linux/types.h> + +/* + * Arguments for how openat2(2) should open the target path. If only @flags and + * @mode are non-zero, then openat2(2) operates very similarly to openat(2). + * + * However, unlike openat(2), unknown or invalid bits in @flags result in + * -EINVAL rather than being silently ignored. @mode must be zero unless one of + * {O_CREAT, O_TMPFILE} are set. + * + * @flags: O_* flags. + * @mode: O_CREAT/O_TMPFILE file mode. + * @resolve: RESOLVE_* flags. + */ +struct open_how { + __u64 flags; + __u64 mode; + __u64 resolve; +}; + +/* 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 /* _UAPI_LINUX_OPENAT2_H */