hostfs creates a new inode for each opened or created file, which created useless inode allocations and forbade identifying a host file with a kernel inode.

Fix this uncommon filesystem behavior by tying kernel inodes to host file's inode and device IDs. Even if the host filesystem inodes may be recycled, this cannot happen while a file referencing it is open, which is the case with hostfs. It should be noted that hostfs inode IDs may not be unique for the same hostfs superblock because multiple host's (backed) superblocks may be used.

Delete inodes when dropping them to force backed host's file descriptors closing.

This enables to entirely remove ARCH_EPHEMERAL_INODES, and then makes Landlock fully supported by UML. This is very useful for testing (ongoing and backported) changes.

These changes also factor out and simplify some helpers thanks to the new hostfs_inode_update() and the hostfs_iget() revamp: read_name(), hostfs_create(), hostfs_lookup(), hostfs_mknod(), and hostfs_fill_sb_common().

A following commit with new Landlock tests check this new hostfs inode consistency.

Cc: Anton Ivanov anton.ivanov@cambridgegreys.com Cc: Johannes Berg johannes@sipsolutions.net Cc: Richard Weinberger richard@nod.at Cc: stable@vger.kernel.org # 5.15.x: ce72750f04d6: hostfs: Fix writeback of dirty pages Cc: stable@vger.kernel.org # 5.15+ Signed-off-by: Mickaël Salaün mic@digikod.net Link: https://lore.kernel.org/r/20230309165455.175131-2-mic@digikod.net --- arch/Kconfig | 7 -- arch/um/Kconfig | 1 - fs/hostfs/hostfs.h | 1 + fs/hostfs/hostfs_kern.c | 213 +++++++++++++++++++------------------- fs/hostfs/hostfs_user.c | 1 + security/landlock/Kconfig | 2 +- 6 files changed, 109 insertions(+), 116 deletions(-)

diff --git a/arch/Kconfig b/arch/Kconfig index e3511afbb7f2..d5f0841ac3c1 100644 --- a/arch/Kconfig +++ b/arch/Kconfig @@ -1156,13 +1156,6 @@ config COMPAT_32BIT_TIME config ARCH_NO_PREEMPT bool

-config ARCH_EPHEMERAL_INODES - def_bool n - help - An arch should select this symbol if it doesn't keep track of inode - instances on its own, but instead relies on something else (e.g. the - host kernel for an UML kernel). - config ARCH_SUPPORTS_RT bool

diff --git a/arch/um/Kconfig b/arch/um/Kconfig index 541a9b18e343..4057d5267c6a 100644 --- a/arch/um/Kconfig +++ b/arch/um/Kconfig @@ -5,7 +5,6 @@ menu "UML-specific options" config UML bool default y - select ARCH_EPHEMERAL_INODES select ARCH_HAS_FORTIFY_SOURCE select ARCH_HAS_GCOV_PROFILE_ALL select ARCH_HAS_KCOV diff --git a/fs/hostfs/hostfs.h b/fs/hostfs/hostfs.h index 69cb796f6270..0239e3af3945 100644 --- a/fs/hostfs/hostfs.h +++ b/fs/hostfs/hostfs.h @@ -65,6 +65,7 @@ struct hostfs_stat { unsigned long long blocks; unsigned int maj; unsigned int min; + dev_t dev; };

extern int stat_file(const char *path, struct hostfs_stat *p, int fd); diff --git a/fs/hostfs/hostfs_kern.c b/fs/hostfs/hostfs_kern.c index 28b4f15c19eb..19496f732016 100644 --- a/fs/hostfs/hostfs_kern.c +++ b/fs/hostfs/hostfs_kern.c @@ -26,6 +26,7 @@ struct hostfs_inode_info { fmode_t mode; struct inode vfs_inode; struct mutex open_mutex; + dev_t dev; };

static inline struct hostfs_inode_info *HOSTFS_I(struct inode *inode) @@ -182,14 +183,6 @@ static char *follow_link(char *link) return ERR_PTR(n); }

-static struct inode *hostfs_iget(struct super_block *sb) -{ - struct inode *inode = new_inode(sb); - if (!inode) - return ERR_PTR(-ENOMEM); - return inode; -} - static int hostfs_statfs(struct dentry *dentry, struct kstatfs *sf) { /* @@ -228,6 +221,7 @@ static struct inode *hostfs_alloc_inode(struct super_block *sb) return NULL; hi->fd = -1; hi->mode = 0; + hi->dev = 0; inode_init_once(&hi->vfs_inode); mutex_init(&hi->open_mutex); return &hi->vfs_inode; @@ -240,6 +234,7 @@ static void hostfs_evict_inode(struct inode *inode) if (HOSTFS_I(inode)->fd != -1) { close_file(&HOSTFS_I(inode)->fd); HOSTFS_I(inode)->fd = -1; + HOSTFS_I(inode)->dev = 0; } }

@@ -265,6 +260,7 @@ static int hostfs_show_options(struct seq_file *seq, struct dentry *root) static const struct super_operations hostfs_sbops = { .alloc_inode = hostfs_alloc_inode, .free_inode = hostfs_free_inode, + .drop_inode = generic_delete_inode, .evict_inode = hostfs_evict_inode, .statfs = hostfs_statfs, .show_options = hostfs_show_options, @@ -512,18 +508,31 @@ static const struct address_space_operations hostfs_aops = { .write_end = hostfs_write_end, };

-static int read_name(struct inode *ino, char *name) +static int hostfs_inode_update(struct inode *ino, const struct hostfs_stat *st) +{ + set_nlink(ino, st->nlink); + i_uid_write(ino, st->uid); + i_gid_write(ino, st->gid); + ino->i_atime = + (struct timespec64){ st->atime.tv_sec, st->atime.tv_nsec }; + ino->i_mtime = + (struct timespec64){ st->mtime.tv_sec, st->mtime.tv_nsec }; + ino->i_ctime = + (struct timespec64){ st->ctime.tv_sec, st->ctime.tv_nsec }; + ino->i_size = st->size; + ino->i_blocks = st->blocks; + return 0; +} + +static int hostfs_inode_set(struct inode *ino, void *data) { + struct hostfs_stat *st = data; dev_t rdev; - struct hostfs_stat st; - int err = stat_file(name, &st, -1); - if (err) - return err;

/* Reencode maj and min with the kernel encoding.*/ - rdev = MKDEV(st.maj, st.min); + rdev = MKDEV(st->maj, st->min);

- switch (st.mode & S_IFMT) { + switch (st->mode & S_IFMT) { case S_IFLNK: ino->i_op = &hostfs_link_iops; break; @@ -535,7 +544,7 @@ static int read_name(struct inode *ino, char *name) case S_IFBLK: case S_IFIFO: case S_IFSOCK: - init_special_inode(ino, st.mode & S_IFMT, rdev); + init_special_inode(ino, st->mode & S_IFMT, rdev); ino->i_op = &hostfs_iops; break; case S_IFREG: @@ -547,17 +556,42 @@ static int read_name(struct inode *ino, char *name) return -EIO; }

- ino->i_ino = st.ino; - ino->i_mode = st.mode; - set_nlink(ino, st.nlink); - i_uid_write(ino, st.uid); - i_gid_write(ino, st.gid); - ino->i_atime = (struct timespec64){ st.atime.tv_sec, st.atime.tv_nsec }; - ino->i_mtime = (struct timespec64){ st.mtime.tv_sec, st.mtime.tv_nsec }; - ino->i_ctime = (struct timespec64){ st.ctime.tv_sec, st.ctime.tv_nsec }; - ino->i_size = st.size; - ino->i_blocks = st.blocks; - return 0; + HOSTFS_I(ino)->dev = st->dev; + ino->i_ino = st->ino; + ino->i_mode = st->mode; + return hostfs_inode_update(ino, st); +} + +static int hostfs_inode_test(struct inode *inode, void *data) +{ + const struct hostfs_stat *st = data; + + return inode->i_ino == st->ino && HOSTFS_I(inode)->dev == st->dev; +} + +static struct inode *hostfs_iget(struct super_block *sb, char *name) +{ + struct inode *inode; + struct hostfs_stat st; + int err = stat_file(name, &st, -1); + + if (err) + return ERR_PTR(err); + + inode = iget5_locked(sb, st.ino, hostfs_inode_test, hostfs_inode_set, + &st); + if (!inode) + return ERR_PTR(-ENOMEM); + + if (inode->i_state & I_NEW) { + unlock_new_inode(inode); + } else { + spin_lock(&inode->i_lock); + hostfs_inode_update(inode, &st); + spin_unlock(&inode->i_lock); + } + + return inode; }

static int hostfs_create(struct mnt_idmap *idmap, struct inode *dir, @@ -565,62 +599,48 @@ static int hostfs_create(struct mnt_idmap *idmap, struct inode *dir, { struct inode *inode; char *name; - int error, fd; - - inode = hostfs_iget(dir->i_sb); - if (IS_ERR(inode)) { - error = PTR_ERR(inode); - goto out; - } + int fd;

- error = -ENOMEM; name = dentry_name(dentry); if (name == NULL) - goto out_put; + return -ENOMEM;

fd = file_create(name, mode & 0777); - if (fd < 0) - error = fd; - else - error = read_name(inode, name); + if (fd < 0) { + __putname(name); + return fd; + }

+ inode = hostfs_iget(dir->i_sb, name); __putname(name); - if (error) - goto out_put; + if (IS_ERR(inode)) + return PTR_ERR(inode);

HOSTFS_I(inode)->fd = fd; HOSTFS_I(inode)->mode = FMODE_READ | FMODE_WRITE; d_instantiate(dentry, inode); return 0; - - out_put: - iput(inode); - out: - return error; }

static struct dentry *hostfs_lookup(struct inode *ino, struct dentry *dentry, unsigned int flags) { - struct inode *inode; + struct inode *inode = NULL; char *name; - int err; - - inode = hostfs_iget(ino->i_sb); - if (IS_ERR(inode)) - goto out;

- err = -ENOMEM; name = dentry_name(dentry); - if (name) { - err = read_name(inode, name); - __putname(name); - } - if (err) { - iput(inode); - inode = (err == -ENOENT) ? NULL : ERR_PTR(err); + if (name == NULL) + return ERR_PTR(-ENOMEM); + + inode = hostfs_iget(ino->i_sb, name); + __putname(name); + if (IS_ERR(inode)) { + if (PTR_ERR(inode) == -ENOENT) + inode = NULL; + else + return ERR_CAST(inode); } - out: + return d_splice_alias(inode, dentry); }

@@ -704,35 +724,23 @@ static int hostfs_mknod(struct mnt_idmap *idmap, struct inode *dir, char *name; int err;

- inode = hostfs_iget(dir->i_sb); - if (IS_ERR(inode)) { - err = PTR_ERR(inode); - goto out; - } - - err = -ENOMEM; name = dentry_name(dentry); if (name == NULL) - goto out_put; + return -ENOMEM;

err = do_mknod(name, mode, MAJOR(dev), MINOR(dev)); - if (err) - goto out_free; + if (err) { + __putname(name); + return err; + }

- err = read_name(inode, name); + inode = hostfs_iget(dir->i_sb, name); __putname(name); - if (err) - goto out_put; + if (IS_ERR(inode)) + return PTR_ERR(inode);

d_instantiate(dentry, inode); return 0; - - out_free: - __putname(name); - out_put: - iput(inode); - out: - return err; }

static int hostfs_rename2(struct mnt_idmap *idmap, @@ -929,49 +937,40 @@ static int hostfs_fill_sb_common(struct super_block *sb, void *d, int silent) sb->s_maxbytes = MAX_LFS_FILESIZE; err = super_setup_bdi(sb); if (err) - goto out; + return err;

/* NULL is printed as '(null)' by printf(): avoid that. */ if (req_root == NULL) req_root = "";

- err = -ENOMEM; sb->s_fs_info = host_root_path = kasprintf(GFP_KERNEL, "%s/%s", root_ino, req_root); if (host_root_path == NULL) - goto out; - - root_inode = new_inode(sb); - if (!root_inode) - goto out; + return -ENOMEM;

- err = read_name(root_inode, host_root_path); - if (err) - goto out_put; + root_inode = hostfs_iget(sb, host_root_path); + if (IS_ERR(root_inode)) + return PTR_ERR(root_inode);

if (S_ISLNK(root_inode->i_mode)) { - char *name = follow_link(host_root_path); - if (IS_ERR(name)) { - err = PTR_ERR(name); - goto out_put; - } - err = read_name(root_inode, name); + char *name; + + iput(root_inode); + name = follow_link(host_root_path); + if (IS_ERR(name)) + return PTR_ERR(name); + + root_inode = hostfs_iget(sb, name); kfree(name); - if (err) - goto out_put; + if (IS_ERR(root_inode)) + return PTR_ERR(root_inode); }

- err = -ENOMEM; sb->s_root = d_make_root(root_inode); if (sb->s_root == NULL) - goto out; + return -ENOMEM;

return 0; - -out_put: - iput(root_inode); -out: - return err; }

static struct dentry *hostfs_read_sb(struct file_system_type *type, diff --git a/fs/hostfs/hostfs_user.c b/fs/hostfs/hostfs_user.c index 5ecc4706172b..840619e39a1a 100644 --- a/fs/hostfs/hostfs_user.c +++ b/fs/hostfs/hostfs_user.c @@ -36,6 +36,7 @@ static void stat64_to_hostfs(const struct stat64 *buf, struct hostfs_stat *p) p->blocks = buf->st_blocks; p->maj = os_major(buf->st_rdev); p->min = os_minor(buf->st_rdev); + p->dev = buf->st_dev; }

int stat_file(const char *path, struct hostfs_stat *p, int fd) diff --git a/security/landlock/Kconfig b/security/landlock/Kconfig index 8e33c4e8ffb8..c1e862a38410 100644 --- a/security/landlock/Kconfig +++ b/security/landlock/Kconfig @@ -2,7 +2,7 @@

config SECURITY_LANDLOCK bool "Landlock support" - depends on SECURITY && !ARCH_EPHEMERAL_INODES + depends on SECURITY select SECURITY_PATH help Landlock is a sandboxing mechanism that enables processes to restrict

Replace supports_overlayfs() with supports_filesystem() to be able to check several filesystems. This will be useful in a following commit.

Only check for overlay filesystem once in the setup step, and then rely on self->skip_test.

Cc: Guenter Roeck groeck@chromium.org Cc: Jeff Xu jeffxu@google.com Cc: stable@vger.kernel.org Signed-off-by: Mickaël Salaün mic@digikod.net Link: https://lore.kernel.org/r/20230309165455.175131-4-mic@digikod.net --- tools/testing/selftests/landlock/fs_test.c | 36 ++++++++++++++-------- 1 file changed, 23 insertions(+), 13 deletions(-)

diff --git a/tools/testing/selftests/landlock/fs_test.c b/tools/testing/selftests/landlock/fs_test.c index 0438651f61d2..c1e655fc06bb 100644 --- a/tools/testing/selftests/landlock/fs_test.c +++ b/tools/testing/selftests/landlock/fs_test.c @@ -107,8 +107,10 @@ static bool fgrep(FILE *const inf, const char *const str) return false; }

-static bool supports_overlayfs(void) +static bool supports_filesystem(const char *const filesystem) { + char str[32]; + int len; bool res; FILE *const inf = fopen("/proc/filesystems", "r");

@@ -119,7 +121,12 @@ static bool supports_overlayfs(void) if (!inf) return true;

- res = fgrep(inf, "nodev\toverlay\n"); + len = snprintf(str, sizeof(str), "nodev\t%s\n", filesystem); + if (len >= sizeof(str)) + /* Ignores too-long filesystem names. */ + return true; + + res = fgrep(inf, str); fclose(inf); return res; } @@ -4044,14 +4051,17 @@ static const char (*merge_sub_files[])[] = { * └── work */

-/* clang-format off */ -FIXTURE(layout2_overlay) {}; -/* clang-format on */ +FIXTURE(layout2_overlay) +{ + bool skip_test; +};

FIXTURE_SETUP(layout2_overlay) { - if (!supports_overlayfs()) - SKIP(return, "overlayfs is not supported"); + if (!supports_filesystem("overlay")) { + self->skip_test = true; + SKIP(return, "overlayfs is not supported (setup)"); + }

prepare_layout(_metadata);

@@ -4089,8 +4099,8 @@ FIXTURE_SETUP(layout2_overlay)

FIXTURE_TEARDOWN(layout2_overlay) { - if (!supports_overlayfs()) - SKIP(return, "overlayfs is not supported"); + if (self->skip_test) + SKIP(return, "overlayfs is not supported (teardown)");

EXPECT_EQ(0, remove_path(lower_do1_fl3)); EXPECT_EQ(0, remove_path(lower_dl1_fl2)); @@ -4123,8 +4133,8 @@ FIXTURE_TEARDOWN(layout2_overlay)

TEST_F_FORK(layout2_overlay, no_restriction) { - if (!supports_overlayfs()) - SKIP(return, "overlayfs is not supported"); + if (self->skip_test) + SKIP(return, "overlayfs is not supported (test)");

ASSERT_EQ(0, test_open(lower_fl1, O_RDONLY)); ASSERT_EQ(0, test_open(lower_dl1, O_RDONLY)); @@ -4289,8 +4299,8 @@ TEST_F_FORK(layout2_overlay, same_content_different_file) size_t i; const char *path_entry;

- if (!supports_overlayfs()) - SKIP(return, "overlayfs is not supported"); + if (self->skip_test) + SKIP(return, "overlayfs is not supported (test)");

/* Sets rules on base directories (i.e. outside overlay scope). */ ruleset_fd = create_ruleset(_metadata, ACCESS_RW, layer1_base);

Add generic and read-only tests for 7 pseudo filesystems to make sure they have a consistent inode management, which is required for Landlock's file hierarchy identification: - ramfs - tmpfs - cgroup - cgroup2 - proc - sysfs - hostfs

Update related kernel configuration to support these new filesystems, and sort all entries. If these filesystems are not supported by the kernel running tests, the related tests are skipped.

Expanding variants, this adds 35 new tests for layout3_fs: - tag_inode_dir_parent - tag_inode_dir_mnt - tag_inode_dir_child - tag_inode_dir_file - release_inodes

The hostfs filesystem, only available for an User-Mode Linux kernel, is special because we cannot explicitly mount it. The layout3_fs.hostfs variant tests are skipped if the current test directory is not backed by this filesystem.

The layout3_fs.hostfs.tag_inode_dir_child and layout3_fs.hostfs.tag_inode_file tests pass thanks to a previous commit fixing hostfs inode management. Without this fix, the deny-by-default policy would apply and all access requests would be denied.

Cc: stable@vger.kernel.org # 5.15.x: 63e6b2a42342: selftests/harness: Run TEARDOWN for ASSERT failures Cc: stable@vger.kernel.org # 5.15.x: 79ee8aa31d51: selftests/harness: Pass variant to teardown Cc: stable@vger.kernel.org # 5.15+ Signed-off-by: Mickaël Salaün mic@digikod.net Link: https://lore.kernel.org/r/20230309165455.175131-6-mic@digikod.net --- tools/testing/selftests/landlock/config | 8 +- tools/testing/selftests/landlock/fs_test.c | 285 +++++++++++++++++++++ 2 files changed, 291 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/landlock/config b/tools/testing/selftests/landlock/config index 0f0a65287bac..5501108d00b7 100644 --- a/tools/testing/selftests/landlock/config +++ b/tools/testing/selftests/landlock/config @@ -1,7 +1,11 @@ +CONFIG_CGROUPS=y +CONFIG_CGROUP_SCHED=y CONFIG_OVERLAY_FS=y +CONFIG_PROC_FS=y +CONFIG_SECURITY=y CONFIG_SECURITY_LANDLOCK=y CONFIG_SECURITY_PATH=y -CONFIG_SECURITY=y CONFIG_SHMEM=y -CONFIG_TMPFS_XATTR=y +CONFIG_SYSFS=y CONFIG_TMPFS=y +CONFIG_TMPFS_XATTR=y diff --git a/tools/testing/selftests/landlock/fs_test.c b/tools/testing/selftests/landlock/fs_test.c index de29c8c9e194..f6a80ad738e1 100644 --- a/tools/testing/selftests/landlock/fs_test.c +++ b/tools/testing/selftests/landlock/fs_test.c @@ -10,6 +10,7 @@ #define _GNU_SOURCE #include <fcntl.h> #include <linux/landlock.h> +#include <linux/magic.h> #include <sched.h> #include <stdio.h> #include <string.h> @@ -19,6 +20,7 @@ #include <sys/sendfile.h> #include <sys/stat.h> #include <sys/sysmacros.h> +#include <sys/vfs.h> #include <unistd.h>

#include "common.h" @@ -121,6 +123,10 @@ static bool supports_filesystem(const char *const filesystem) if (!inf) return true;

+ /* filesystem can be null for bind mounts. */ + if (!filesystem) + return true; + len = snprintf(str, sizeof(str), "nodev\t%s\n", filesystem); if (len >= sizeof(str)) /* Ignores too-long filesystem names. */ @@ -131,6 +137,19 @@ static bool supports_filesystem(const char *const filesystem) return res; }

+static bool cwd_matches_fs(unsigned int fs_magic) +{ + struct statfs statfs_buf; + + if (!fs_magic) + return true; + + if (statfs(".", &statfs_buf)) + return true; + + return statfs_buf.f_type == fs_magic; +} + static void mkdir_parents(struct __test_metadata *const _metadata, const char *const path) { @@ -307,11 +326,13 @@ static void remove_layout1(struct __test_metadata *const _metadata) EXPECT_EQ(0, remove_path(file1_s1d3)); EXPECT_EQ(0, remove_path(file1_s1d2)); EXPECT_EQ(0, remove_path(file1_s1d1)); + EXPECT_EQ(0, remove_path(dir_s1d3));

EXPECT_EQ(0, remove_path(file2_s2d3)); EXPECT_EQ(0, remove_path(file1_s2d3)); EXPECT_EQ(0, remove_path(file1_s2d2)); EXPECT_EQ(0, remove_path(file1_s2d1)); + EXPECT_EQ(0, remove_path(dir_s2d2));

EXPECT_EQ(0, remove_path(file1_s3d1)); EXPECT_EQ(0, remove_path(dir_s3d3)); @@ -4471,4 +4492,268 @@ TEST_F_FORK(layout2_overlay, same_content_different_file) } }

+FIXTURE(layout3_fs) +{ + bool has_created_dir; + bool has_created_file; + char *dir_path; + bool skip_test; +}; + +FIXTURE_VARIANT(layout3_fs) +{ + const struct mnt_opt mnt; + const char *const file_path; + unsigned int cwd_fs_magic; +}; + +/* clang-format off */ +FIXTURE_VARIANT_ADD(layout3_fs, tmpfs) { + /* clang-format on */ + .mnt = mnt_tmp, + .file_path = file1_s1d1, +}; + +FIXTURE_VARIANT_ADD(layout3_fs, ramfs) { + .mnt = { + .type = "ramfs", + .data = "mode=700", + }, + .file_path = TMP_DIR "/dir/file", +}; + +FIXTURE_VARIANT_ADD(layout3_fs, cgroup) { + .mnt = { + .type = "cgroup", + }, + .file_path = TMP_DIR "/test/tasks", +}; + +FIXTURE_VARIANT_ADD(layout3_fs, cgroup2) { + .mnt = { + .type = "cgroup2", + }, + .file_path = TMP_DIR "/test/cgroup.procs", +}; + +FIXTURE_VARIANT_ADD(layout3_fs, proc) { + .mnt = { + .type = "proc", + }, + .file_path = TMP_DIR "/self/status", +}; + +FIXTURE_VARIANT_ADD(layout3_fs, sysfs) { + .mnt = { + .type = "sysfs", + }, + .file_path = TMP_DIR "/kernel/notes", +}; + +FIXTURE_VARIANT_ADD(layout3_fs, hostfs) { + .mnt = { + .source = TMP_DIR, + .flags = MS_BIND, + }, + .file_path = TMP_DIR "/dir/file", + .cwd_fs_magic = HOSTFS_SUPER_MAGIC, +}; + +FIXTURE_SETUP(layout3_fs) +{ + struct stat statbuf; + const char *slash; + size_t dir_len; + + if (!supports_filesystem(variant->mnt.type) || + !cwd_matches_fs(variant->cwd_fs_magic)) { + self->skip_test = true; + SKIP(return, "this filesystem is not supported (setup)"); + } + + slash = strrchr(variant->file_path, '/'); + ASSERT_NE(slash, NULL); + dir_len = (size_t)slash - (size_t)variant->file_path; + ASSERT_LT(0, dir_len); + self->dir_path = malloc(dir_len + 1); + self->dir_path[dir_len] = '\0'; + strncpy(self->dir_path, variant->file_path, dir_len); + + prepare_layout_opt(_metadata, &variant->mnt); + + /* Creates directory when required. */ + if (stat(self->dir_path, &statbuf)) { + set_cap(_metadata, CAP_DAC_OVERRIDE); + EXPECT_EQ(0, mkdir(self->dir_path, 0700)) + { + TH_LOG("Failed to create directory "%s": %d %s", + self->dir_path, errno, strerror(errno)); + free(self->dir_path); + self->dir_path = NULL; + } + self->has_created_dir = true; + clear_cap(_metadata, CAP_DAC_OVERRIDE); + } + + /* Creates file when required. */ + if (stat(variant->file_path, &statbuf)) { + int fd; + + set_cap(_metadata, CAP_DAC_OVERRIDE); + fd = creat(variant->file_path, 0600); + EXPECT_LE(0, fd) + { + TH_LOG("Failed to create file "%s": %d %s", + variant->file_path, errno, strerror(errno)); + } + EXPECT_EQ(0, close(fd)); + self->has_created_file = true; + clear_cap(_metadata, CAP_DAC_OVERRIDE); + } +} + +FIXTURE_TEARDOWN(layout3_fs) +{ + if (self->skip_test) + SKIP(return, "this filesystem is not supported (teardown)"); + + if (self->has_created_file) { + set_cap(_metadata, CAP_DAC_OVERRIDE); + /* + * Don't check for error because the file might already + * have been removed (cf. release_inode test). + */ + unlink(variant->file_path); + clear_cap(_metadata, CAP_DAC_OVERRIDE); + } + + if (self->has_created_dir) { + set_cap(_metadata, CAP_DAC_OVERRIDE); + /* + * Don't check for error because the directory might already + * have been removed (cf. release_inode test). + */ + rmdir(self->dir_path); + clear_cap(_metadata, CAP_DAC_OVERRIDE); + } + free(self->dir_path); + self->dir_path = NULL; + + cleanup_layout(_metadata); +} + +static void layer3_fs_tag_inode(struct __test_metadata *const _metadata, + FIXTURE_DATA(layout3_fs) * self, + const FIXTURE_VARIANT(layout3_fs) * variant, + const char *const rule_path) +{ + const struct rule layer1_allow_read_file[] = { + { + .path = rule_path, + .access = LANDLOCK_ACCESS_FS_READ_FILE, + }, + {}, + }; + const struct landlock_ruleset_attr layer2_deny_everything_attr = { + .handled_access_fs = LANDLOCK_ACCESS_FS_READ_FILE, + }; + const char *const dev_null_path = "/dev/null"; + int ruleset_fd; + + if (self->skip_test) + SKIP(return, "this filesystem is not supported (test)"); + + /* Checks without Landlock. */ + EXPECT_EQ(0, test_open(dev_null_path, O_RDONLY | O_CLOEXEC)); + EXPECT_EQ(0, test_open(variant->file_path, O_RDONLY | O_CLOEXEC)); + + ruleset_fd = create_ruleset(_metadata, LANDLOCK_ACCESS_FS_READ_FILE, + layer1_allow_read_file); + EXPECT_LE(0, ruleset_fd); + enforce_ruleset(_metadata, ruleset_fd); + EXPECT_EQ(0, close(ruleset_fd)); + + EXPECT_EQ(EACCES, test_open(dev_null_path, O_RDONLY | O_CLOEXEC)); + EXPECT_EQ(0, test_open(variant->file_path, O_RDONLY | O_CLOEXEC)); + + /* Forbids directory reading. */ + ruleset_fd = + landlock_create_ruleset(&layer2_deny_everything_attr, + sizeof(layer2_deny_everything_attr), 0); + EXPECT_LE(0, ruleset_fd); + enforce_ruleset(_metadata, ruleset_fd); + EXPECT_EQ(0, close(ruleset_fd)); + + /* Checks with Landlock and forbidden access. */ + EXPECT_EQ(EACCES, test_open(dev_null_path, O_RDONLY | O_CLOEXEC)); + EXPECT_EQ(EACCES, test_open(variant->file_path, O_RDONLY | O_CLOEXEC)); +} + +/* Matrix of tests to check file hierarchy evaluation. */ + +TEST_F_FORK(layout3_fs, tag_inode_dir_parent) +{ + /* The current directory must not be the root for this test. */ + layer3_fs_tag_inode(_metadata, self, variant, "."); +} + +TEST_F_FORK(layout3_fs, tag_inode_dir_mnt) +{ + layer3_fs_tag_inode(_metadata, self, variant, TMP_DIR); +} + +TEST_F_FORK(layout3_fs, tag_inode_dir_child) +{ + layer3_fs_tag_inode(_metadata, self, variant, self->dir_path); +} + +TEST_F_FORK(layout3_fs, tag_inode_file) +{ + layer3_fs_tag_inode(_metadata, self, variant, variant->file_path); +} + +/* Light version of layout1.release_inodes */ +TEST_F_FORK(layout3_fs, release_inodes) +{ + const struct rule layer1[] = { + { + .path = TMP_DIR, + .access = LANDLOCK_ACCESS_FS_READ_DIR, + }, + {}, + }; + int ruleset_fd; + + if (self->skip_test) + SKIP(return, "this filesystem is not supported (test)"); + + /* Clean up for the teardown to not fail. */ + if (self->has_created_file) + EXPECT_EQ(0, remove_path(variant->file_path)); + + if (self->has_created_dir) + /* Don't check for error because of cgroup specificities. */ + remove_path(self->dir_path); + + ruleset_fd = + create_ruleset(_metadata, LANDLOCK_ACCESS_FS_READ_DIR, layer1); + ASSERT_LE(0, ruleset_fd); + + /* Unmount the filesystem while it is being used by a ruleset. */ + set_cap(_metadata, CAP_SYS_ADMIN); + ASSERT_EQ(0, umount(TMP_DIR)); + clear_cap(_metadata, CAP_SYS_ADMIN); + + /* Replaces with a new mount point to simplify FIXTURE_TEARDOWN. */ + set_cap(_metadata, CAP_SYS_ADMIN); + ASSERT_EQ(0, mount("tmp", TMP_DIR, "tmpfs", 0, "size=4m,mode=700")); + clear_cap(_metadata, CAP_SYS_ADMIN); + + enforce_ruleset(_metadata, ruleset_fd); + ASSERT_EQ(0, close(ruleset_fd)); + + /* Checks that access to the new mount point is denied. */ + ASSERT_EQ(EACCES, test_open(TMP_DIR, O_RDONLY)); +} + TEST_HARNESS_MAIN

On 06/06/2023 15:12, Roberto Sassu wrote:

On Thu, 2023-03-09 at 17:54 +0100, Mickaël Salaün wrote:

...

hostfs creates a new inode for each opened or created file, which created useless inode allocations and forbade identifying a host file with a kernel inode.

Fix this uncommon filesystem behavior by tying kernel inodes to host file's inode and device IDs. Even if the host filesystem inodes may be recycled, this cannot happen while a file referencing it is open, which is the case with hostfs. It should be noted that hostfs inode IDs may not be unique for the same hostfs superblock because multiple host's (backed) superblocks may be used.

I hoped that this patch solved an issue when testing the inode_setsecurity and inode_getsecurity combination. Unfortunately, it does not work, since after inode_setsecurity the inode is dropped. At the time inode_getsecurity is called, the security blob is lost.

Indeed, this is because inode[sg]etsecurity() rely on inode's xattr, which are not handled by hostfs. Why not simply use overlayfs with an upper tmpfs that supports xattr? This patch might be needed to such scenario though.

Roberto

...

Delete inodes when dropping them to force backed host's file descriptors closing.

This enables to entirely remove ARCH_EPHEMERAL_INODES, and then makes Landlock fully supported by UML. This is very useful for testing (ongoing and backported) changes.

These changes also factor out and simplify some helpers thanks to the new hostfs_inode_update() and the hostfs_iget() revamp: read_name(), hostfs_create(), hostfs_lookup(), hostfs_mknod(), and hostfs_fill_sb_common().

A following commit with new Landlock tests check this new hostfs inode consistency.

Cc: Anton Ivanov anton.ivanov@cambridgegreys.com Cc: Johannes Berg johannes@sipsolutions.net Cc: Richard Weinberger richard@nod.at Cc: stable@vger.kernel.org # 5.15.x: ce72750f04d6: hostfs: Fix writeback of dirty pages Cc: stable@vger.kernel.org # 5.15+ Signed-off-by: Mickaël Salaün mic@digikod.net Link: https://lore.kernel.org/r/20230309165455.175131-2-mic@digikod.net

---

arch/Kconfig | 7 -- arch/um/Kconfig | 1 - fs/hostfs/hostfs.h | 1 + fs/hostfs/hostfs_kern.c | 213 +++++++++++++++++++------------------- fs/hostfs/hostfs_user.c | 1 + security/landlock/Kconfig | 2 +- 6 files changed, 109 insertions(+), 116 deletions(-)

diff --git a/arch/Kconfig b/arch/Kconfig index e3511afbb7f2..d5f0841ac3c1 100644 --- a/arch/Kconfig +++ b/arch/Kconfig @@ -1156,13 +1156,6 @@ config COMPAT_32BIT_TIME config ARCH_NO_PREEMPT bool -config ARCH_EPHEMERAL_INODES

• def_bool n
• help

•  An arch should select this symbol if it doesn't keep track of inode
  

•  instances on its own, but instead relies on something else (e.g. the
  

•  host kernel for an UML kernel).
  

• config ARCH_SUPPORTS_RT bool

diff --git a/arch/um/Kconfig b/arch/um/Kconfig index 541a9b18e343..4057d5267c6a 100644 --- a/arch/um/Kconfig +++ b/arch/um/Kconfig @@ -5,7 +5,6 @@ menu "UML-specific options" config UML bool default y

• select ARCH_EPHEMERAL_INODES select ARCH_HAS_FORTIFY_SOURCE select ARCH_HAS_GCOV_PROFILE_ALL select ARCH_HAS_KCOV

diff --git a/fs/hostfs/hostfs.h b/fs/hostfs/hostfs.h index 69cb796f6270..0239e3af3945 100644 --- a/fs/hostfs/hostfs.h +++ b/fs/hostfs/hostfs.h @@ -65,6 +65,7 @@ struct hostfs_stat { unsigned long long blocks; unsigned int maj; unsigned int min;

• dev_t dev; };

extern int stat_file(const char *path, struct hostfs_stat *p, int fd); diff --git a/fs/hostfs/hostfs_kern.c b/fs/hostfs/hostfs_kern.c index 28b4f15c19eb..19496f732016 100644 --- a/fs/hostfs/hostfs_kern.c +++ b/fs/hostfs/hostfs_kern.c @@ -26,6 +26,7 @@ struct hostfs_inode_info { fmode_t mode; struct inode vfs_inode; struct mutex open_mutex;

• dev_t dev; };

static inline struct hostfs_inode_info *HOSTFS_I(struct inode *inode) @@ -182,14 +183,6 @@ static char *follow_link(char *link) return ERR_PTR(n); } -static struct inode *hostfs_iget(struct super_block *sb) -{

• struct inode *inode = new_inode(sb);
• if (!inode)

• return ERR_PTR(-ENOMEM);
  

• return inode;

-}

• static int hostfs_statfs(struct dentry *dentry, struct kstatfs *sf) { /*

@@ -228,6 +221,7 @@ static struct inode *hostfs_alloc_inode(struct super_block *sb) return NULL; hi->fd = -1; hi->mode = 0;

• hi->dev = 0; inode_init_once(&hi->vfs_inode); mutex_init(&hi->open_mutex); return &hi->vfs_inode;

@@ -240,6 +234,7 @@ static void hostfs_evict_inode(struct inode *inode) if (HOSTFS_I(inode)->fd != -1) { close_file(&HOSTFS_I(inode)->fd); HOSTFS_I(inode)->fd = -1;

• HOSTFS_I(inode)->dev = 0;
  

  } }

@@ -265,6 +260,7 @@ static int hostfs_show_options(struct seq_file *seq, struct dentry *root) static const struct super_operations hostfs_sbops = { .alloc_inode = hostfs_alloc_inode, .free_inode = hostfs_free_inode,

• .drop_inode = generic_delete_inode, .evict_inode = hostfs_evict_inode, .statfs = hostfs_statfs, .show_options = hostfs_show_options,

@@ -512,18 +508,31 @@ static const struct address_space_operations hostfs_aops = { .write_end = hostfs_write_end, }; -static int read_name(struct inode *ino, char *name) +static int hostfs_inode_update(struct inode *ino, const struct hostfs_stat *st) +{

• set_nlink(ino, st->nlink);
• i_uid_write(ino, st->uid);
• i_gid_write(ino, st->gid);
• ino->i_atime =

• (struct timespec64){ st->atime.tv_sec, st->atime.tv_nsec };
  

• ino->i_mtime =

• (struct timespec64){ st->mtime.tv_sec, st->mtime.tv_nsec };
  

• ino->i_ctime =

• (struct timespec64){ st->ctime.tv_sec, st->ctime.tv_nsec };
  

• ino->i_size = st->size;
• ino->i_blocks = st->blocks;
• return 0;

+}

+static int hostfs_inode_set(struct inode *ino, void *data) {

• struct hostfs_stat *st = data; dev_t rdev;

• struct hostfs_stat st;
• int err = stat_file(name, &st, -1);
• if (err)

• return err;
  

/* Reencode maj and min with the kernel encoding.*/

• rdev = MKDEV(st.maj, st.min);

• rdev = MKDEV(st->maj, st->min);

• switch (st.mode & S_IFMT) {

• switch (st->mode & S_IFMT) { case S_IFLNK: ino->i_op = &hostfs_link_iops; break;

@@ -535,7 +544,7 @@ static int read_name(struct inode *ino, char *name) case S_IFBLK: case S_IFIFO: case S_IFSOCK:

• init_special_inode(ino, st.mode & S_IFMT, rdev);
  

• init_special_inode(ino, st->mode & S_IFMT, rdev);
  

  ino->i_op = &hostfs_iops; break; case S_IFREG:

@@ -547,17 +556,42 @@ static int read_name(struct inode *ino, char *name) return -EIO; }

• ino->i_ino = st.ino;
• ino->i_mode = st.mode;
• set_nlink(ino, st.nlink);
• i_uid_write(ino, st.uid);
• i_gid_write(ino, st.gid);
• ino->i_atime = (struct timespec64){ st.atime.tv_sec, st.atime.tv_nsec };
• ino->i_mtime = (struct timespec64){ st.mtime.tv_sec, st.mtime.tv_nsec };
• ino->i_ctime = (struct timespec64){ st.ctime.tv_sec, st.ctime.tv_nsec };
• ino->i_size = st.size;
• ino->i_blocks = st.blocks;
• return 0;

• HOSTFS_I(ino)->dev = st->dev;
• ino->i_ino = st->ino;
• ino->i_mode = st->mode;
• return hostfs_inode_update(ino, st);

+}

+static int hostfs_inode_test(struct inode *inode, void *data) +{

• const struct hostfs_stat *st = data;
• return inode->i_ino == st->ino && HOSTFS_I(inode)->dev == st->dev;

+}

+static struct inode *hostfs_iget(struct super_block *sb, char *name) +{

• struct inode *inode;
• struct hostfs_stat st;
• int err = stat_file(name, &st, -1);
• if (err)

• return ERR_PTR(err);
  

• inode = iget5_locked(sb, st.ino, hostfs_inode_test, hostfs_inode_set,

• 	     &st);
  

• if (!inode)

• return ERR_PTR(-ENOMEM);
  

• if (inode->i_state & I_NEW) {

• unlock_new_inode(inode);
  

• } else {

• spin_lock(&inode->i_lock);
  

• hostfs_inode_update(inode, &st);
  

• spin_unlock(&inode->i_lock);
  

• }
• return inode; }

static int hostfs_create(struct mnt_idmap *idmap, struct inode *dir, @@ -565,62 +599,48 @@ static int hostfs_create(struct mnt_idmap *idmap, struct inode *dir, { struct inode *inode; char *name;

• int error, fd;
• inode = hostfs_iget(dir->i_sb);
• if (IS_ERR(inode)) {

• error = PTR_ERR(inode);
  

• goto out;
  

• }

• int fd;

• error = -ENOMEM; name = dentry_name(dentry); if (name == NULL)

• goto out_put;
  

• return -ENOMEM;
  

fd = file_create(name, mode & 0777);

• if (fd < 0)

• error = fd;
  

• else

• error = read_name(inode, name);
  

• if (fd < 0) {

• __putname(name);
  

• return fd;
  

• }

• inode = hostfs_iget(dir->i_sb, name); __putname(name);

• if (error)

• goto out_put;
  

• if (IS_ERR(inode))

• return PTR_ERR(inode);
  

HOSTFS_I(inode)->fd = fd; HOSTFS_I(inode)->mode = FMODE_READ | FMODE_WRITE; d_instantiate(dentry, inode); return 0;

• out_put:
• iput(inode);
• out:
• return error; }

static struct dentry *hostfs_lookup(struct inode *ino, struct dentry *dentry, unsigned int flags) {

• struct inode *inode;

• struct inode *inode = NULL; char *name;

• int err;
• inode = hostfs_iget(ino->i_sb);
• if (IS_ERR(inode))

• goto out;
  

• err = -ENOMEM; name = dentry_name(dentry);
• if (name) {

• err = read_name(inode, name);
  

• __putname(name);
  

• }
• if (err) {

• iput(inode);
  

• inode = (err == -ENOENT) ? NULL : ERR_PTR(err);
  

• if (name == NULL)

• return ERR_PTR(-ENOMEM);
  

• inode = hostfs_iget(ino->i_sb, name);
• __putname(name);
• if (IS_ERR(inode)) {

• if (PTR_ERR(inode) == -ENOENT)
  

• 	inode = NULL;
  

• else
  

• 	return ERR_CAST(inode);
  

  }

• out:

• return d_splice_alias(inode, dentry); }

@@ -704,35 +724,23 @@ static int hostfs_mknod(struct mnt_idmap *idmap, struct inode *dir, char *name; int err;

• inode = hostfs_iget(dir->i_sb);
• if (IS_ERR(inode)) {

• err = PTR_ERR(inode);
  

• goto out;
  

• }
• err = -ENOMEM; name = dentry_name(dentry); if (name == NULL)

• goto out_put;
  

• return -ENOMEM;
  

err = do_mknod(name, mode, MAJOR(dev), MINOR(dev));

• if (err)

• goto out_free;
  

• if (err) {

• __putname(name);
  

• return err;
  

• }

• err = read_name(inode, name);

• inode = hostfs_iget(dir->i_sb, name); __putname(name);

• if (err)

• goto out_put;
  

• if (IS_ERR(inode))

• return PTR_ERR(inode);
  

d_instantiate(dentry, inode); return 0;

• out_free:
• __putname(name);
• out_put:
• iput(inode);
• out:
• return err; }

static int hostfs_rename2(struct mnt_idmap *idmap, @@ -929,49 +937,40 @@ static int hostfs_fill_sb_common(struct super_block *sb, void *d, int silent) sb->s_maxbytes = MAX_LFS_FILESIZE; err = super_setup_bdi(sb); if (err)

• goto out;
  

• return err;
  

/* NULL is printed as '(null)' by printf(): avoid that. */ if (req_root == NULL) req_root = "";

• err = -ENOMEM; sb->s_fs_info = host_root_path = kasprintf(GFP_KERNEL, "%s/%s", root_ino, req_root); if (host_root_path == NULL)

• goto out;
  

• root_inode = new_inode(sb);
• if (!root_inode)

• goto out;
  

• return -ENOMEM;
  

• err = read_name(root_inode, host_root_path);
• if (err)

• goto out_put;
  

• root_inode = hostfs_iget(sb, host_root_path);
• if (IS_ERR(root_inode))

• return PTR_ERR(root_inode);
  

if (S_ISLNK(root_inode->i_mode)) {

• char *name = follow_link(host_root_path);
  

• if (IS_ERR(name)) {
  

• 	err = PTR_ERR(name);
  

• 	goto out_put;
  

• }
  

• err = read_name(root_inode, name);
  

• char *name;
  

• iput(root_inode);
  

• name = follow_link(host_root_path);
  

• if (IS_ERR(name))
  

• 	return PTR_ERR(name);
  

• root_inode = hostfs_iget(sb, name);
  

  kfree(name);

• if (err)
  

• 	goto out_put;
  

• if (IS_ERR(root_inode))
  

• 	return PTR_ERR(root_inode);
  

  }

• err = -ENOMEM; sb->s_root = d_make_root(root_inode); if (sb->s_root == NULL)

• goto out;
  

• return -ENOMEM;
  

return 0;

-out_put:

• iput(root_inode);

-out:

• return err; }

static struct dentry *hostfs_read_sb(struct file_system_type *type, diff --git a/fs/hostfs/hostfs_user.c b/fs/hostfs/hostfs_user.c index 5ecc4706172b..840619e39a1a 100644 --- a/fs/hostfs/hostfs_user.c +++ b/fs/hostfs/hostfs_user.c @@ -36,6 +36,7 @@ static void stat64_to_hostfs(const struct stat64 *buf, struct hostfs_stat *p) p->blocks = buf->st_blocks; p->maj = os_major(buf->st_rdev); p->min = os_minor(buf->st_rdev);

• p->dev = buf->st_dev; }

int stat_file(const char *path, struct hostfs_stat *p, int fd) diff --git a/security/landlock/Kconfig b/security/landlock/Kconfig index 8e33c4e8ffb8..c1e862a38410 100644 --- a/security/landlock/Kconfig +++ b/security/landlock/Kconfig @@ -2,7 +2,7 @@ config SECURITY_LANDLOCK bool "Landlock support"

• depends on SECURITY && !ARCH_EPHEMERAL_INODES

• depends on SECURITY select SECURITY_PATH help Landlock is a sandboxing mechanism that enables processes to restrict