Subject: Re: WARNING in kcm_exit_net (2)

From: Eric Biggers <[email-masked]>
Date: Sun, 8 Apr 2018 12:38:10 -0700

On Wed, Nov 29, 2017 at 10:08:01PM -0800, syzbot wrote:
> Hello,
> 
> syzkaller hit the following crash on
> 1d3b78bbc6e983fabb3fbf91b76339bf66e4a12c
> git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next.git/master
> compiler: gcc (GCC) 7.1.1 20170620
> .config is attached
> Raw console output is attached.
> 
> Unfortunately, I don't have any reproducer for this bug yet.
> 
> 
> WARNING: CPU: 1 PID: 4099 at net/kcm/kcmsock.c:2014 kcm_exit_net+0x317/0x360
> net/kcm/kcmsock.c:2014
> Kernel panic - not syncing: panic_on_warn set ...
> 
> CPU: 1 PID: 4099 Comm: kworker/u4:9 Not tainted 4.14.0+ #129
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> Workqueue: netns cleanup_net
> device lo entered promiscuous mode
> Call Trace:
>  __dump_stack lib/dump_stack.c:17 [inline]
>  dump_stack+0x194/0x257 lib/dump_stack.c:53
>  panic+0x1e4/0x41c kernel/panic.c:183
>  __warn+0x1dc/0x200 kernel/panic.c:547
>  report_bug+0x211/0x2d0 lib/bug.c:184
>  fixup_bug.part.11+0x37/0x80 arch/x86/kernel/traps.c:177
>  fixup_bug arch/x86/kernel/traps.c:246 [inline]
>  do_error_trap+0x2d7/0x3e0 arch/x86/kernel/traps.c:295
>  do_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:314
>  invalid_op+0x18/0x20 arch/x86/entry/entry_64.S:926
> RIP: 0010:kcm_exit_net+0x317/0x360 net/kcm/kcmsock.c:2014
> RSP: 0000:ffff8801d9d27198 EFLAGS: 00010293
> RAX: ffff8801c0884540 RBX: 1ffff1003b3a4e33 RCX: ffffffff84a738e7
> RDX: 0000000000000000 RSI: 0000000000000004 RDI: 0000000000000286
> RBP: ffff8801d9d27260 R08: 0000000000000003 R09: 1ffff1003b3a4e0c
> R10: ffff8801c0884540 R11: 0000000000000003 R12: 1ffff1003b3a4e37
> R13: ffff8801d9d27238 R14: ffff8801c5fec8a0 R15: ffff8801c4b62e40
>  ops_exit_list.isra.6+0xae/0x150 net/core/net_namespace.c:142
>  cleanup_net+0x5c7/0xb60 net/core/net_namespace.c:484
>  process_one_work+0xbfd/0x1be0 kernel/workqueue.c:2112
>  worker_thread+0x223/0x1990 kernel/workqueue.c:2246
>  kthread+0x37a/0x440 kernel/kthread.c:238
>  ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:437
> Dumping ftrace buffer:
>    (ftrace buffer empty)
> Kernel Offset: disabled
> Rebooting in 86400 seconds..
> 
> 
> ---
> This bug is generated by a dumb bot. It may contain errors.
> See https://goo.gl/tpsmEJ for details.
> Direct all questions to [email-masked].
> Please credit me with: Reported-by: syzbot <[email-masked]>
> 
> syzbot will keep track of this bug report.
> Once a fix for this bug is committed, please reply to this email with:
> #syz fix: exact-commit-title
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> If it's a one-off invalid bug report, please reply with:
> #syz invalid

No reproducer, this last occurred on Dec 26 (103 days ago, commit fba961ab29e),
and there have been several potentially relevant KCM fixes since then such as
581e7226a5d ("kcm: Only allow TCP sockets to be attached to a KCM mux") and
e5571240236 ("kcm: Check if sk_user_data already set in kcm_attach").  So I am
invalidating this for syzbot, but if anyone thinks this may still be a bug then
feel free to look into it.

#syz invalid

Eric