CVE-2024-26780

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

afunix: Fix task hung while purging oobskb in GC.

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

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

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

unixnotinflight() uses listdelinit() to unlink the socket, so the prefetched next socket forms a loop itself and listforeachentry_safe() never stops.

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

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:preemptcount arch/x86/include/asm/preempt.h:26 [inline] RIP: 0010:checkkcovmode kernel/kcov.c:173 [inline] RIP: 0010:sanitizercovtracepc+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: ffff88802a5a3b80 RSI: ffffffff8968488d RDI: ffff88807b077f70 RBP: ffffc900033efbb0 R08: 0000000000000001 R09: fffffbfff27a900c R10: ffffffff93d48067 R11: ffffffff8ae000eb R12: ffff88807b077800 R13: dffffc0000000000 R14: ffff88807b077e40 R15: 0000000000000001 FS: 0000000000000000(0000) GS:ffff8880b9500000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000564f4fc1e3a8 CR3: 000000000d57a000 CR4: 00000000003506f0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: <NMI> </NMI> <TASK> unixgc+0x563/0x13b0 net/unix/garbage.c:319 unixreleasesock+0xa93/0xf80 net/unix/afunix.c:683 unixrelease+0x91/0xf0 net/unix/afunix.c:1064 _sockrelease+0xb0/0x270 net/socket.c:659 sockclose+0x1c/0x30 net/socket.c:1421 _fput+0x270/0xb80 fs/filetable.c:376 taskworkrun+0x14f/0x250 kernel/taskwork.c:180 exittaskwork include/linux/taskwork.h:38 [inline] doexit+0xa8a/0x2ad0 kernel/exit.c:871 dogroupexit+0xd4/0x2a0 kernel/exit.c:1020 _dosysexitgroup kernel/exit.c:1031 [inline] _sesysexitgroup kernel/exit.c:1029 [inline] _x64sysexitgroup+0x3e/0x50 kernel/exit.c:1029 dosyscallx64 arch/x86/entry/common.c:52 [inline] dosyscall64+0xd5/0x270 arch/x86/entry/common.c:83 entrySYSCALL64afterhwframe+0x6f/0x77 RIP: 0033:0x7f9d6cbdac09 Code: Unable to access opcode bytes at 0x7f9d6cbdabdf. RSP: 002b:00007fff5952feb8 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7 RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f9d6cbdac09 RDX: 000000000000003c RSI: 00000000000000e7 RDI: 0000000000000000 RBP: 00007f9d6cc552b0 R08: ffffffffffffffb8 R09: 0000000000000006 R10: 0000000000000006 R11: 0000000000000246 R12: 00007f9d6cc552b0 R13: 0000000000000000 R14: 00007f9d6cc55d00 R15: 00007f9d6cbabe70 </TASK>