On 10/9/23 9:43AM, Max Kellermann wrote:
One important implementation detail of the posix_acl_create() function is that it applies the umask to the "mode" parameter. If CONFIG_FS_POSIX_ACL is disabled, this detail is missing and the umask may not get applied. This patch adds the missing code to posix_acl_create() and to three filesystems that omit the posix_acl_create() call if their individual ACL support is disabled (CONFIG_EXT2_FS_POSIX_ACL, CONFIG_JFS_POSIX_ACL, CONFIG_CEPH_FS_POSIX_ACL). If posix_acl_create() never gets called, the umask needs to be applied anyway. This bug used to be exploitable easily with O_TMPFILE (see https://bugzilla.kernel.org/show_bug.cgi?id=203625) but that part was fixed by commit ac6800e279a2 ("fs: Add missing umask strip in vfs_tmpfile") last year. The bug may not be reachable by userspace anymore, but since it is apparently still necessary to apply the umask again in posix_acl_create(), there is no reason to assume it's not necessary with ACL support is disabled. Signed-off-by: Max Kellermann <max.kellermann@xxxxxxxxx>
Acked-by: Dave Kleikamp <dave.kleikamp@xxxxxxxxxx>
--- fs/ceph/super.h | 6 ++++++ fs/ext2/acl.h | 6 ++++++ fs/jfs/jfs_acl.h | 6 ++++++ include/linux/posix_acl.h | 1 + 4 files changed, 19 insertions(+) diff --git a/fs/ceph/super.h b/fs/ceph/super.h index 51c7f2b14f6f..58349639bd57 100644 --- a/fs/ceph/super.h +++ b/fs/ceph/super.h @@ -1194,6 +1194,12 @@ static inline void ceph_forget_all_cached_acls(struct inode *inode) static inline int ceph_pre_init_acls(struct inode *dir, umode_t *mode, struct ceph_acl_sec_ctx *as_ctx) { + /* usually, the umask is applied by posix_acl_create(), but if + * ACL support is disabled at compile time, we need to do it + * here, because posix_acl_create() will never be called + */ + *mode &= ~current_umask(); + return 0; } static inline void ceph_init_inode_acls(struct inode *inode, diff --git a/fs/ext2/acl.h b/fs/ext2/acl.h index 4a8443a2b8ec..0ecaa9c20c0c 100644 --- a/fs/ext2/acl.h +++ b/fs/ext2/acl.h @@ -67,6 +67,12 @@ extern int ext2_init_acl (struct inode *, struct inode *);static inline int ext2_init_acl (struct inode *inode, struct inode *dir){ + /* usually, the umask is applied by posix_acl_create(), but if + * ACL support is disabled at compile time, we need to do it + * here, because posix_acl_create() will never be called + */ + inode->i_mode &= ~current_umask(); + return 0; } #endif diff --git a/fs/jfs/jfs_acl.h b/fs/jfs/jfs_acl.h index f892e54d0fcd..64a05e663a45 100644 --- a/fs/jfs/jfs_acl.h +++ b/fs/jfs/jfs_acl.h @@ -17,6 +17,12 @@ int jfs_init_acl(tid_t, struct inode *, struct inode *); static inline int jfs_init_acl(tid_t tid, struct inode *inode, struct inode *dir) { + /* usually, the umask is applied by posix_acl_create(), but if + * ACL support is disabled at compile time, we need to do it + * here, because posix_acl_create() will never be called + */ + inode->i_mode &= ~current_umask(); + return 0; }diff --git a/include/linux/posix_acl.h b/include/linux/posix_acl.hindex 0e65b3d634d9..54bc9b1061ca 100644 --- a/include/linux/posix_acl.h +++ b/include/linux/posix_acl.h @@ -128,6 +128,7 @@ static inline void cache_no_acl(struct inode *inode) static inline int posix_acl_create(struct inode *inode, umode_t *mode, struct posix_acl **default_acl, struct posix_acl **acl) { + *mode &= ~current_umask(); *default_acl = *acl = NULL; return 0; }
