diff options
Diffstat (limited to 'security/landlock')
| -rw-r--r-- | security/landlock/errata/abi-1.h | 23 | ||||
| -rw-r--r-- | security/landlock/fs.c | 41 |
2 files changed, 55 insertions, 9 deletions
diff --git a/security/landlock/errata/abi-1.h b/security/landlock/errata/abi-1.h index 3f099555f059..315ea7e0fe50 100644 --- a/security/landlock/errata/abi-1.h +++ b/security/landlock/errata/abi-1.h @@ -22,3 +22,26 @@ * from their original mount points. */ LANDLOCK_ERRATUM(3) + +/** + * DOC: erratum_4 + * + * Erratum 4: Creation of whiteout objects + * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + * + * This fix changes the access rights required for the creation of whiteout + * objects through :manpage:`mknod(2)`, :manpage:`renameat2(2)`, or + * :manpage:`link(2)`. Creating whiteout objects is now guarded by + * ``LANDLOCK_ACCESS_FS_MAKE_REG`` instead of ``LANDLOCK_ACCESS_FS_MAKE_CHAR``. + * + * Whiteout objects are used in OverlayFS to mark the absence of a file in an + * upper file system. Despite being created with ``S_IFCHR``, whiteout objects + * do not count as character devices. + * + * Impact: + * + * Sandboxed programs that create OverlayFS whiteouts (such as fuse-overlayfs) + * now require ``LANDLOCK_ACCESS_FS_MAKE_REG`` instead of + * ``LANDLOCK_ACCESS_FS_MAKE_CHAR``. + */ +LANDLOCK_ERRATUM(4) diff --git a/security/landlock/fs.c b/security/landlock/fs.c index f7e5e4ef9eac..8fc7f82a374a 100644 --- a/security/landlock/fs.c +++ b/security/landlock/fs.c @@ -20,6 +20,7 @@ #include <linux/falloc.h> #include <linux/fs.h> #include <linux/init.h> +#include <linux/kdev_t.h> #include <linux/kernel.h> #include <linux/limits.h> #include <linux/list.h> @@ -983,7 +984,8 @@ static int current_check_access_path(const struct path *const path, return -EACCES; } -static __attribute_const__ access_mask_t get_mode_access(const umode_t mode) +static __attribute_const__ access_mask_t get_mode_access(const umode_t mode, + const dev_t dev) { switch (mode & S_IFMT) { case S_IFLNK: @@ -991,6 +993,9 @@ static __attribute_const__ access_mask_t get_mode_access(const umode_t mode) case S_IFDIR: return LANDLOCK_ACCESS_FS_MAKE_DIR; case S_IFCHR: + /* Whiteout objects are guarded with MAKE_REG. */ + if (dev == WHITEOUT_DEV) + return LANDLOCK_ACCESS_FS_MAKE_REG; return LANDLOCK_ACCESS_FS_MAKE_CHAR; case S_IFBLK: return LANDLOCK_ACCESS_FS_MAKE_BLOCK; @@ -1007,6 +1012,13 @@ static __attribute_const__ access_mask_t get_mode_access(const umode_t mode) } } +static access_mask_t get_dentry_access(const struct dentry *const dentry) +{ + const struct inode *const inode = d_backing_inode(dentry); + + return get_mode_access(inode->i_mode, inode->i_rdev); +} + static access_mask_t maybe_remove(const struct dentry *const dentry) { if (d_is_negative(dentry)) @@ -1093,6 +1105,7 @@ static bool collect_domain_accesses(const struct landlock_ruleset *const domain, * @new_dentry: Destination file or directory. * @removable: Sets to true if it is a rename operation. * @exchange: Sets to true if it is a rename operation with RENAME_EXCHANGE. + * @whiteout: Sets to true if it is a rename operation with RENAME_WHITEOUT. * * Because of its unprivileged constraints, Landlock relies on file hierarchies * (and not only inodes) to tie access rights to files. Being able to link or @@ -1140,7 +1153,8 @@ static bool collect_domain_accesses(const struct landlock_ruleset *const domain, static int current_check_refer_path(struct dentry *const old_dentry, const struct path *const new_dir, struct dentry *const new_dentry, - const bool removable, const bool exchange) + const bool removable, const bool exchange, + const bool whiteout) { const struct landlock_cred_security *const subject = landlock_get_applicable_subject(current_cred(), any_fs, NULL); @@ -1159,18 +1173,25 @@ static int current_check_refer_path(struct dentry *const old_dentry, if (exchange) { if (unlikely(d_is_negative(new_dentry))) return -ENOENT; - access_request_parent1 = - get_mode_access(d_backing_inode(new_dentry)->i_mode); + access_request_parent1 = get_dentry_access(new_dentry); } else { access_request_parent1 = 0; } - access_request_parent2 = - get_mode_access(d_backing_inode(old_dentry)->i_mode); + access_request_parent2 = get_dentry_access(old_dentry); if (removable) { access_request_parent1 |= maybe_remove(old_dentry); access_request_parent2 |= maybe_remove(new_dentry); } + /* + * In case of renameat2(2) with RENAME_WHITEOUT, a whiteout object is + * created in the source location, so we require an additional access + * right there. + */ + if (whiteout) + access_request_parent1 |= + get_mode_access(S_IFCHR | WHITEOUT_MODE, WHITEOUT_DEV); + /* The mount points are the same for old and new paths, cf. EXDEV. */ if (old_dentry->d_parent == new_dir->dentry) { /* @@ -1520,7 +1541,7 @@ static int hook_path_link(struct dentry *const old_dentry, struct dentry *const new_dentry) { return current_check_refer_path(old_dentry, new_dir, new_dentry, false, - false); + false, false); } static int hook_path_rename(const struct path *const old_dir, @@ -1531,7 +1552,8 @@ static int hook_path_rename(const struct path *const old_dir, { /* old_dir refers to old_dentry->d_parent and new_dir->mnt */ return current_check_refer_path(old_dentry, new_dir, new_dentry, true, - !!(flags & RENAME_EXCHANGE)); + !!(flags & RENAME_EXCHANGE), + !!(flags & RENAME_WHITEOUT)); } static int hook_path_mkdir(const struct path *const dir, @@ -1544,7 +1566,8 @@ static int hook_path_mknod(const struct path *const dir, struct dentry *const dentry, const umode_t mode, const unsigned int dev) { - return current_check_access_path(dir, get_mode_access(mode)); + return current_check_access_path( + dir, get_mode_access(mode, new_decode_dev(dev))); } static int hook_path_symlink(const struct path *const dir, |