In the Linux kernel, the following vulnerability has been resolved:
btrfs: handle lack of space when cleaning up verity items
When enable_verity() hits the qgroup limit, rollback_verity() needs its
own metadata reservation. When the qgroup limit or lack of space refuses
the rollback, the whole filesystem is forced read-only even though the
qgroup limit was for one subvolume only. Also orphan cleanup at the next
mount fails the same way, so the leftover items are never removed: with
-EDQUOT the subvolume stays unreachable, and with -ENOSPC on a full
filesystem the next read-write mount fails.
Start transactions with btrfs_start_transaction_fallback_global_rsv() in
btrfs_orphan_cleanup(), drop_verity_items() and rollback_verity(). Those
calls only delete items and free the space in the end, so they may use
the global reserve and skip the qgroup limit, which avoids -ENOSPC and
-EDQUOT.