6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx> commit aa82ac51d63328714645c827775d64dbfd9941f3 upstream. syzbot reported another task hung in __unix_gc(). [0] The current while loop assumes that all of the left candidates have oob_skb and calling kfree_skb(oob_skb) releases the remaining candidates. However, I missed a case that oob_skb has self-referencing fd and another fd and the latter sk is placed before the former in the candidate list. Then, the while loop never proceeds, resulting the task hung. __unix_gc() has the same loop just before purging the collected skb, so we can call kfree_skb(oob_skb) there and let __skb_queue_purge() release all inflight sockets. [0]: Sending NMI from CPU 0 to CPUs 1: NMI backtrace for cpu 1 CPU: 1 PID: 2784 Comm: kworker/u4:8 Not tainted 6.8.0-rc4-syzkaller-01028-g71b605d32017 #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/25/2024 Workqueue: events_unbound __unix_gc RIP: 0010:__sanitizer_cov_trace_pc+0x0/0x70 kernel/kcov.c:200 Code: 89 fb e8 23 00 00 00 48 8b 3d 84 f5 1a 0c 48 89 de 5b e9 43 26 57 00 0f 1f 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 <f3> 0f 1e fa 48 8b 04 24 65 48 8b 0d 90 52 70 7e 65 8b 15 91 52 70 RSP: 0018:ffffc9000a17fa78 EFLAGS: 00000287 RAX: ffffffff8a0a6108 RBX: ffff88802b6c2640 RCX: ffff88802c0b3b80 RDX: 0000000000000000 RSI: 0000000000000002 RDI: 0000000000000000 RBP: ffffc9000a17fbf0 R08: ffffffff89383f1d R09: 1ffff1100ee5ff84 R10: dffffc0000000000 R11: ffffed100ee5ff85 R12: 1ffff110056d84ee R13: ffffc9000a17fae0 R14: 0000000000000000 R15: ffffffff8f47b840 FS: 0000000000000000(0000) GS:ffff8880b9500000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007ffef5687ff8 CR3: 0000000029b34000 CR4: 00000000003506f0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: <NMI> </NMI> <TASK> __unix_gc+0xe69/0xf40 net/unix/garbage.c:343 process_one_work kernel/workqueue.c:2633 [inline] process_scheduled_works+0x913/0x1420 kernel/workqueue.c:2706 worker_thread+0xa5f/0x1000 kernel/workqueue.c:2787 kthread+0x2ef/0x390 kernel/kthread.c:388 ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147 ret_from_fork_asm+0x1b/0x30 arch/x86/entry/entry_64.S:242 </TASK> Reported-and-tested-by: syzbot+ecab4d36f920c3574bf9@xxxxxxxxxxxxxxxxxxxxxxxxx Closes: https://syzkaller.appspot.com/bug?extid=ecab4d36f920c3574bf9 Fixes: 25236c91b5ab ("af_unix: Fix task hung while purging oob_skb in GC.") Signed-off-by: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- net/unix/garbage.c | 22 +++++++++------------- 1 file changed, 9 insertions(+), 13 deletions(-) --- a/net/unix/garbage.c +++ b/net/unix/garbage.c @@ -284,9 +284,17 @@ void unix_gc(void) * which are creating the cycle(s). */ skb_queue_head_init(&hitlist); - list_for_each_entry(u, &gc_candidates, link) + list_for_each_entry(u, &gc_candidates, link) { scan_children(&u->sk, inc_inflight, &hitlist); +#if IS_ENABLED(CONFIG_AF_UNIX_OOB) + if (u->oob_skb) { + kfree_skb(u->oob_skb); + u->oob_skb = NULL; + } +#endif + } + /* not_cycle_list contains those sockets which do not make up a * cycle. Restore these to the inflight list. */ @@ -314,18 +322,6 @@ void unix_gc(void) /* Here we are. Hitlist is filled. Die. */ __skb_queue_purge(&hitlist); -#if IS_ENABLED(CONFIG_AF_UNIX_OOB) - while (!list_empty(&gc_candidates)) { - u = list_entry(gc_candidates.next, struct unix_sock, link); - if (u->oob_skb) { - struct sk_buff *skb = u->oob_skb; - - u->oob_skb = NULL; - kfree_skb(skb); - } - } -#endif - spin_lock(&unix_gc_lock); /* There could be io_uring registered files, just push them back to
