In the Linux kernel, the following vulnerability has been resolved:

btrfs: do not BUG_ON() when freeing tree block after error

When freeing a tree block, at btrfs_free_tree_block(), if we fail to
create a delayed reference we don't deal with the error and just do a
BUG_ON(). The error most likely to happen is -ENOMEM, and we have a
comment mentioning that only -ENOMEM can happen, but that is not true,
because in case qgroups are enabled any error returned from
btrfs_qgroup_trace_extent_post() (can be -EUCLEAN or anything returned
from btrfs_search_slot() for example) can be propagated back to
btrfs_free_tree_block().

So stop doing a BUG_ON() and return the error to the callers and make
them abort the transaction to prevent leaking space. Syzbot was
triggering this, likely due to memory allocation failure injection.