Btrfs: allow subvol deletion by unprivileged user with -o user_subvol_rm_allowed

Add a mount option user_subvol_rm_allowed that allows users to delete a
(potentially non-empty!) subvol when they would otherwise we allowed to do
an rmdir(2).  We duplicate the may_delete() checks from the core VFS code
to implement identical security checks (minus the directory size check).
We additionally require that the user has write+exec permission on the
subvol root inode.

Signed-off-by: Sage Weil <sage@newdream.net>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index e5d66b13c175..8db9234f6b41 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1234,6 +1234,7 @@ struct btrfs_root {
 #define BTRFS_MOUNT_FORCE_COMPRESS      (1 << 11)
 #define BTRFS_MOUNT_SPACE_CACHE         (1 << 12)
 #define BTRFS_MOUNT_CLEAR_CACHE         (1 << 13)
+#define BTRFS_MOUNT_USER_SUBVOL_RM_ALLOWED (1 << 14)
 
 #define btrfs_clear_opt(o, opt)         ((o) &= ~BTRFS_MOUNT_##opt)
 #define btrfs_set_opt(o, opt)           ((o) |= BTRFS_MOUNT_##opt)