From: Christian Brauner <christian.brauner@xxxxxxxxxx>
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 <clm@xxxxxx>
Cc: Josef Bacik <josef@xxxxxxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Cc: David Sterba <dsterba@xxxxxxxx>
Cc: linux-btrfs@xxxxxxxxxxxxxxx
Signed-off-by: Christian Brauner <christian.brauner@xxxxxxxxxx>
---
fs/btrfs/ioctl.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 8ec67e52fde3..f332de258058 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);
}
--
2.30.2
