CVE-2024-26780 — af_unix: Fix task hung while purging oob_skb in GC.

Affected: Linux

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

af_unix: Fix task hung while purging oob_skb in GC.

syzbot reported a task hung; at the same time, GC was looping infinitely in list_for_each_entry_safe() for OOB skb. [0]

syzbot demonstrated that the list_for_each_entry_safe() was not actually safe in this case.

A single skb could have references for multiple sockets. If we free such a skb in the list_for_each_entry_safe(), the current and next sockets could be unlinked in a single iteration.

unix_notinflight() uses list_del_init() to unlink the socket, so the prefetched next socket forms a loop itself and list_for_each_entry_safe() never stops.

Here, we must use while() and make sure we always fetch the first socket.

[0]: Sending NMI from CPU 0 to CPUs 1: NMI backtrace for cpu 1 CPU: 1 PID: 5065 Comm: syz-executor236 Not tainted 6.8.0-rc3-syzkaller-00136-g1f719a2f3fa6 #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/25/2024 RIP: 0010:preempt_count arch/x86/include/asm/preempt.h:26 [inline] RIP: 0010:check_kcov_mode kernel/kcov.c:173 [inline] RIP: 0010:__sanitizer_cov_trace_pc+0xd/0x60 kernel/kcov.c:207 Code: cc cc cc cc 66 0f 1f 84 00 00 00 00 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 65 48 8b 14 25 40 c2 03 00 <65> 8b 05 b4 7c 78 7e a9 00 01 ff 00 48 8b 34 24 74 0f f6 c4 01 74 RSP: 0018:ffffc900033efa58 EFLAGS: 00000283 RAX: ffff88807b077800 RBX: ffff88807b077800 RCX: 1ffffffff27b1189 RDX:…

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CVE-2024-26780 — af_unix: Fix task hung while purging oob_skb in GC.