CVE-2024-26750

In the Linux kernel, the following vulnerability has been resolved:
af_unix: Drop oob_skb ref before purging queue in GC. 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>