In the Linux kernel, the following vulnerability has been resolved:
btrfs: release path before iget_failed() in btrfs_read_locked_inode()
In btrfs_read_locked_inode() if we fail to lookup the inode, we jump to
the 'out' label with a path that has a read locked leaf and then we call
iget_failed(). This can result in a ABBA deadlock, since iget_failed()
triggers inode eviction and that causes the release of the delayed inode,
which must lock the delayed inode's mutex, and a task updating a delayed
inode starts by taking the node's mutex and then modifying the inode's
subvolume btree.
Syzbot reported the following lockdep splat for this:
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
btrfs-cleaner/8725 is trying to acquire lock:
ffff0000d6826a48 (&delayed_node->mutex){+.+.}-{4:4}, at: __btrfs_release_delayed_node+0xa0/0x9b0 fs/btrfs/delayed-inode.c:290
but task is already holding lock:
ffff0000dbeba878 (btrfs-tree-00){++++}-{4:4}, at: btrfs_tree_read_lock_nested+0x44/0x2ec fs/btrfs/locking.c:145
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #1 (btrfs-tree-00){++++}-{4:4}:
__lock_release kernel/locking/lockdep.c:5574 [inline]
lock_release+0x198/0x39c kernel/locking/lockdep.c:5889
up_read+0x24/0x3c kernel/locking/rwsem.c:1632
btrfs_tree_read_unlock+0xdc/0x298 fs/btrfs/locking.c:169
btrfs_tree_unlock_rw fs/btrfs/locking.h:218 [inline]
btrfs_search_slot+0xa6c/0x223c fs/btrfs/ctree.c:2133
btrfs_lookup_inode+0xd8/0x38c fs/btrfs/inode-item.c:395
__btrfs_update_delayed_inode+0x124/0xed0 fs/btrfs/delayed-inode.c:1032
btrfs_update_delayed_inode fs/btrfs/delayed-inode.c:1118 [inline]
__btrfs_commit_inode_delayed_items+0x15f8/0x1748 fs/btrfs/delayed-inode.c:1141
__btrfs_run_delayed_items+0x1ac/0x514 fs/btrfs/delayed-inode.c:1176
btrfs_run_delayed_items_nr+0x28/0x38 fs/btrfs/delayed-inode.c:1219
flush_space+0x26c/0xb68 fs/btrfs/space-info.c:828
do_async_reclaim_metadata_space+0x110/0x364 fs/btrfs/space-info.c:1158
btrfs_async_reclaim_metadata_space+0x90/0xd8 fs/btrfs/space-info.c:1226
process_one_work+0x7e8/0x155c kernel/workqueue.c:3263
process_scheduled_works kernel/workqueue.c:3346 [inline]
worker_thread+0x958/0xed8 kernel/workqueue.c:3427
kthread+0x5fc/0x75c kernel/kthread.c:463
ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:844
-> #0 (&delayed_node->mutex){+.+.}-{4:4}:
check_prev_add kernel/locking/lockdep.c:3165 [inline]
check_prevs_add kernel/locking/lockdep.c:3284 [inline]
validate_chain kernel/locking/lockdep.c:3908 [inline]
__lock_acquire+0x1774/0x30a4 kernel/locking/lockdep.c:5237
lock_acquire+0x14c/0x2e0 kernel/locking/lockdep.c:5868
__mutex_lock_common+0x1d0/0x2678 kernel/locking/mutex.c:598
__mutex_lock kernel/locking/mutex.c:760 [inline]
mutex_lock_nested+0x2c/0x38 kernel/locking/mutex.c:812
__btrfs_release_delayed_node+0xa0/0x9b0 fs/btrfs/delayed-inode.c:290
btrfs_release_delayed_node fs/btrfs/delayed-inode.c:315 [inline]
btrfs_remove_delayed_node+0x68/0x84 fs/btrfs/delayed-inode.c:1326
btrfs_evict_inode+0x578/0xe28 fs/btrfs/inode.c:5587
evict+0x414/0x928 fs/inode.c:810
iput_final fs/inode.c:1914 [inline]
iput+0x95c/0xad4 fs/inode.c:1966
iget_failed+0xec/0x134 fs/bad_inode.c:248
btrfs_read_locked_inode+0xe1c/0x1234 fs/btrfs/inode.c:4101
btrfs_iget+0x1b0/0x264 fs/btrfs/inode.c:5837
btrfs_run_defrag_inode fs/btrfs/defrag.c:237 [inline]
btrfs_run_defrag_inodes+0x520/0xdc4 fs/btrf
---truncated---
