[syzbot] [net?] INFO: task hung in unix_dgram_sendmsg

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 1f719a2f3fa6 Merge tag 'net-6.8-rc4' of git://git.kernel.o..
git tree: upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=16a21d04180000
kernel config: https://syzkaller.appspot.com/x/.config?x=53985487b59d9442
dashboard link: https://syzkaller.appspot.com/bug?extid=4fa4a2d1f5a5ee06f006
compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1636f042180000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=141c0cec180000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/b8bd7b1c1c4d/disk-1f719a2f.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/58ee6966cdfc/vmlinux-1f719a2f.xz
kernel image: https://storage.googleapis.com/syzbot-assets/3de15662a476/bzImage-1f719a2f.xz

The issue was bisected to:

commit 1279f9d9dec2d7462823a18c29ad61359e0a007d
Author: Kuniyuki Iwashima <kun...@amazon.com>
Date: Sat Feb 3 18:31:49 2024 +0000

af_unix: Call kfree_skb() for dead unix_(sk)->oob_skb in GC.

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=17e71d7c180000
final oops: https://syzkaller.appspot.com/x/report.txt?x=14171d7c180000
console output: https://syzkaller.appspot.com/x/log.txt?x=10171d7c180000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+4fa4a2...@syzkaller.appspotmail.com
Fixes: 1279f9d9dec2 ("af_unix: Call kfree_skb() for dead unix_(sk)->oob_skb in GC.")

INFO: task klogd:4499 blocked for more than 143 seconds.
Not tainted 6.8.0-rc3-syzkaller-00136-g1f719a2f3fa6 #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:klogd state:D stack:26360 pid:4499 tgid:4499 ppid:1 flags:0x00000002
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5400 [inline]
__schedule+0xf12/0x5c60 kernel/sched/core.c:6727
__schedule_loop kernel/sched/core.c:6802 [inline]
schedule+0xe9/0x280 kernel/sched/core.c:6817
wait_for_unix_gc+0x192/0x200 net/unix/garbage.c:201
unix_dgram_sendmsg+0x10e/0x1d10 net/unix/af_unix.c:1924
sock_sendmsg_nosec net/socket.c:730 [inline]
__sock_sendmsg net/socket.c:745 [inline]
__sys_sendto+0x47f/0x4e0 net/socket.c:2191
__do_sys_sendto net/socket.c:2203 [inline]
__se_sys_sendto net/socket.c:2199 [inline]
__x64_sys_sendto+0xe0/0x1c0 net/socket.c:2199
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xd5/0x270 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x6f/0x77
RIP: 0033:0x7f52bb0e69b5
RSP: 002b:00007ffc4e4eb038 EFLAGS: 00000246 ORIG_RAX: 000000000000002c
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f52bb0e69b5
RDX: 0000000000000058 RSI: 000055b5f9c3e420 RDI: 0000000000000003
RBP: 000055b5f9c382c0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000004000 R11: 0000000000000246 R12: 0000000000000013
R13: 00007f52bb274212 R14: 00007ffc4e4eb138 R15: 0000000000000000
</TASK>
INFO: task dhcpcd:4723 blocked for more than 143 seconds.
Not tainted 6.8.0-rc3-syzkaller-00136-g1f719a2f3fa6 #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:dhcpcd state:D stack:26384 pid:4723 tgid:4723 ppid:1 flags:0x00000002
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5400 [inline]
__schedule+0xf12/0x5c60 kernel/sched/core.c:6727
__schedule_loop kernel/sched/core.c:6802 [inline]
schedule+0xe9/0x280 kernel/sched/core.c:6817
wait_for_unix_gc+0x192/0x200 net/unix/garbage.c:201
unix_dgram_sendmsg+0x10e/0x1d10 net/unix/af_unix.c:1924
sock_sendmsg_nosec net/socket.c:730 [inline]
__sock_sendmsg net/socket.c:745 [inline]
sock_write_iter+0x50a/0x5c0 net/socket.c:1160
call_write_iter include/linux/fs.h:2085 [inline]
new_sync_write fs/read_write.c:497 [inline]
vfs_write+0x6de/0x1110 fs/read_write.c:590
ksys_write+0x1f8/0x260 fs/read_write.c:643
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xd5/0x270 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x6f/0x77
RIP: 0033:0x7f09e4d40bf2
RSP: 002b:00007ffdd90b9f68 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 000055f6a34d4030 RCX: 00007f09e4d40bf2
RDX: 0000000000000047 RSI: 00007ffdd90b9f80 RDI: 0000000000000005
RBP: 00007ffdd90b9f80 R08: 0000000000000008 R09: 0000000000000036
R10: 0000000000000000 R11: 0000000000000246 R12: 000055f6a22eeefc
R13: 00007ffdd90ba3b0 R14: 000055f6a35abbb0 R15: 0000000000000001
</TASK>
INFO: task udevd:5066 blocked for more than 143 seconds.
Not tainted 6.8.0-rc3-syzkaller-00136-g1f719a2f3fa6 #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:udevd state:D stack:26920 pid:5066 tgid:5066 ppid:4510 flags:0x00000006
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5400 [inline]
__schedule+0xf12/0x5c60 kernel/sched/core.c:6727
__schedule_loop kernel/sched/core.c:6802 [inline]
schedule+0xe9/0x280 kernel/sched/core.c:6817
wait_for_unix_gc+0x192/0x200 net/unix/garbage.c:201
unix_dgram_sendmsg+0x10e/0x1d10 net/unix/af_unix.c:1924
sock_sendmsg_nosec net/socket.c:730 [inline]
__sock_sendmsg net/socket.c:745 [inline]
sock_write_iter+0x50a/0x5c0 net/socket.c:1160
call_write_iter include/linux/fs.h:2085 [inline]
new_sync_write fs/read_write.c:497 [inline]
vfs_write+0x6de/0x1110 fs/read_write.c:590
ksys_write+0x1f8/0x260 fs/read_write.c:643
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xd5/0x270 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x6f/0x77
RIP: 0033:0x7f5dea316bf2
RSP: 002b:00007ffe87a832d8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f5dea316bf2
RDX: 0000000000000000 RSI: 00007ffe87a8332f RDI: 000000000000000a
RBP: 00007ffe87a8332f R08: 0000000000000001 R09: bff9cdc4d7b79566
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000000000a
R13: 00007f5dea6d7ae0 R14: 0000000000000000 R15: 0000564f4f9ec2c0
</TASK>

Showing all locks held in the system:
1 lock held by khungtaskd/29:
#0: ffffffff8d7ad160 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:298 [inline]
#0: ffffffff8d7ad160 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:750 [inline]
#0: ffffffff8d7ad160 (rcu_read_lock){....}-{1:2}, at: debug_show_all_locks+0x75/0x340 kernel/locking/lockdep.c:6614
2 locks held by getty/4820:
#0: ffff88802b6b90a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x24/0x80 drivers/tty/tty_ldisc.c:243
#1: ffffc900015d02f0 (&ldata->atomic_read_lock){+.+.}-{3:3}, at: n_tty_read+0xfca/0x1490 drivers/tty/n_tty.c:2201
1 lock held by syz-executor236/5065:

=============================================

NMI backtrace for cpu 0
CPU: 0 PID: 29 Comm: khungtaskd Not tainted 6.8.0-rc3-syzkaller-00136-g1f719a2f3fa6 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/25/2024
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0xd9/0x1b0 lib/dump_stack.c:106
nmi_cpu_backtrace+0x27b/0x390 lib/nmi_backtrace.c:113
nmi_trigger_cpumask_backtrace+0x29c/0x300 lib/nmi_backtrace.c:62
trigger_all_cpu_backtrace include/linux/nmi.h:160 [inline]
check_hung_uninterruptible_tasks kernel/hung_task.c:222 [inline]
watchdog+0xf87/0x1210 kernel/hung_task.c:379
kthread+0x2c6/0x3b0 kernel/kthread.c:388
ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x1b/0x30 arch/x86/entry/entry_64.S:242
</TASK>
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: 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>
unix_gc+0x563/0x13b0 net/unix/garbage.c:319
unix_release_sock+0xa93/0xf80 net/unix/af_unix.c:683
unix_release+0x91/0xf0 net/unix/af_unix.c:1064
__sock_release+0xb0/0x270 net/socket.c:659
sock_close+0x1c/0x30 net/socket.c:1421
__fput+0x270/0xb80 fs/file_table.c:376
task_work_run+0x14f/0x250 kernel/task_work.c:180
exit_task_work include/linux/task_work.h:38 [inline]
do_exit+0xa8a/0x2ad0 kernel/exit.c:871
do_group_exit+0xd4/0x2a0 kernel/exit.c:1020
__do_sys_exit_group kernel/exit.c:1031 [inline]
__se_sys_exit_group kernel/exit.c:1029 [inline]
__x64_sys_exit_group+0x3e/0x50 kernel/exit.c:1029
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xd5/0x270 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+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>
INFO: NMI handler (nmi_cpu_backtrace_handler) took too long to run: 1.801 msecs


---
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syzbot will keep track of this issue. See:
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For information about bisection process see: https://goo.gl/tpsmEJ#bisection

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup

[Kuniyuki Iwashima]

From: syzbot <syzbot+4fa4a2...@syzkaller.appspotmail.com>
Date: Fri, 09 Feb 2024 11:02:22 -0800

> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: 1f719a2f3fa6 Merge tag 'net-6.8-rc4' of git://git.kernel.o..
> git tree: upstream
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=16a21d04180000
> kernel config: https://syzkaller.appspot.com/x/.config?x=53985487b59d9442
> dashboard link: https://syzkaller.appspot.com/bug?extid=4fa4a2d1f5a5ee06f006
> compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1636f042180000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=141c0cec180000

I'll look into it.

Thanks.

[Kuniyuki Iwashima]

From: syzbot <syzbot+4fa4a2...@syzkaller.appspotmail.com>
Date: Fri, 09 Feb 2024 11:02:22 -0800

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 1279f9d9dec2d7462823a18c29ad61359e0a007d

diff --git a/net/unix/garbage.c b/net/unix/garbage.c
index 3e4b986de94b..51acf795f096 100644
--- a/net/unix/garbage.c
+++ b/net/unix/garbage.c
@@ -340,10 +340,11 @@ static void __unix_gc(struct work_struct *work)
__skb_queue_purge(&hitlist);

#if IS_ENABLED(CONFIG_AF_UNIX_OOB)
- list_for_each_entry_safe(u, next, &gc_candidates, link) {
- struct sk_buff *skb = u->oob_skb;
+ 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;

- if (skb) {
u->oob_skb = NULL;
kfree_skb(skb);
}

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-and-tested-by: syzbot+4fa4a2...@syzkaller.appspotmail.com

Tested on:

commit: 1279f9d9 af_unix: Call kfree_skb() for dead unix_(sk)-..
git tree: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=15c46df4180000
kernel config: https://syzkaller.appspot.com/x/.config?x=878fbcf532b1a170

dashboard link: https://syzkaller.appspot.com/bug?extid=4fa4a2d1f5a5ee06f006
compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40

patch: https://syzkaller.appspot.com/x/patch.diff?x=16376320180000

Note: testing is done by a robot and is best-effort only.