[v4,12/21] btrfs/ioctl: check whether fs{g,u}id are mapped during subvolume creation

Commit Message

Christian Brauner July 27, 2021, 10:48 a.m. UTC

From: Christian Brauner <[e-mail]>

When a new subvolume is created btrfs currently doesn't check whether the
fs{g,u}id of the caller actually have a mapping in the user namespace attached
to the filesystem. The vfs always checks this to make sure that the caller's
fs{g,u}id can be represented on-disk. This is most relevant for filesystems
that can be mounted inside user namespaces but it is in general a good
hardening measure to prevent unrepresentable {g,u}ids from being written to
disk.
Since we want to support idmapped mounts for btrfs ioctls to create subvolumes
in follow-up patches this becomes important since we want to make sure the
fs{g,u}id of the caller as mapped according to the idmapped mount can be
represented on-disk. Simply add the missing fsuidgid_has_mapping() line from
the vfs may_create() version to btrfs_may_create().

Cc: Chris Mason <[e-mail]>
Cc: Josef Bacik <[e-mail]>
Cc: Christoph Hellwig <[e-mail]>
Cc: David Sterba <[e-mail]>
Cc: [e-mail]
Reviewed-by: Josef Bacik <[e-mail]>
Signed-off-by: Christian Brauner <[e-mail]>
---
/* v2 */
unchanged

/* v3 */
unchanged

/* v4 */
unchanged
---
 fs/btrfs/ioctl.c | 2 ++
 1 file changed, 2 insertions(+)

Patch

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 0ba98e08a029..7a6a886df7c4 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -870,6 +870,8 @@  static inline int btrfs_may_create(struct inode *dir, struct dentry *child)
 		return -EEXIST;
 	if (IS_DEADDIR(dir))
 		return -ENOENT;
+	if (!fsuidgid_has_mapping(dir->i_sb, &init_user_ns))
+		return -EOVERFLOW;
 	return inode_permission(&init_user_ns, dir, MAY_WRITE | MAY_EXEC);
 }