Re: WARNING in strp_data_ready

[Dmitry Vyukov]

On Wed, Dec 27, 2017 at 8:09 PM, Tom Herbert <tom@xxxxxxxxxxxxxxx> wrote:
> Did you try the patch I posted?

Hi Tom,

No. And I didn't know I need to. Why?
If you think the patch needs additional testing, you can ask syzbot to
test it. See https://github.com/google/syzkaller/blob/master/docs/syzbot.md#communication-with-syzbot
Otherwise proceed with committing it. Or what are we waiting for?

Thanks



> On Wed, Dec 27, 2017 at 10:25 AM, Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote:
>> On Wed, Dec 6, 2017 at 4:44 PM, Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote:
>>>> <john.fastabend@xxxxxxxxx> wrote:
>>>>> On 10/24/2017 08:20 AM, syzbot wrote:
>>>>>> Hello,
>>>>>>
>>>>>> syzkaller hit the following crash on 73d3393ada4f70fa3df5639c8d438f2f034c0ecb
>>>>>> git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/master
>>>>>> compiler: gcc (GCC) 7.1.1 20170620
>>>>>> .config is attached
>>>>>> Raw console output is attached.
>>>>>> C reproducer is attached
>>>>>> syzkaller reproducer is attached. See https://goo.gl/kgGztJ
>>>>>> for information about syzkaller reproducers
>>>>>>
>>>>>>
>>>>>> WARNING: CPU: 0 PID: 2996 at ./include/net/sock.h:1505 sock_owned_by_me include/net/sock.h:1505 [inline]
>>>>>> WARNING: CPU: 0 PID: 2996 at ./include/net/sock.h:1505 sock_owned_by_user include/net/sock.h:1511 [inline]
>>>>>> WARNING: CPU: 0 PID: 2996 at ./include/net/sock.h:1505 strp_data_ready+0x2b7/0x390 net/strparser/strparser.c:404
>>>>>> Kernel panic - not syncing: panic_on_warn set ...
>>>>>>
>>>>>> CPU: 0 PID: 2996 Comm: syzkaller142210 Not tainted 4.14.0-rc5+ #138
>>>>>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
>>>>>> Call Trace:
>>>>>>  <IRQ>
>>>>>>  __dump_stack lib/dump_stack.c:16 [inline]
>>>>>>  dump_stack+0x194/0x257 lib/dump_stack.c:52
>>>>>>  panic+0x1e4/0x417 kernel/panic.c:181
>>>>>>  __warn+0x1c4/0x1d9 kernel/panic.c:542
>>>>>>  report_bug+0x211/0x2d0 lib/bug.c:183
>>>>>>  fixup_bug+0x40/0x90 arch/x86/kernel/traps.c:178
>>>>>>  do_trap_no_signal arch/x86/kernel/traps.c:212 [inline]
>>>>>>  do_trap+0x260/0x390 arch/x86/kernel/traps.c:261
>>>>>>  do_error_trap+0x120/0x390 arch/x86/kernel/traps.c:298
>>>>>>  do_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:311
>>>>>>  invalid_op+0x18/0x20 arch/x86/entry/entry_64.S:905
>>>>>> RIP: 0010:sock_owned_by_me include/net/sock.h:1505 [inline]
>>>>>> RIP: 0010:sock_owned_by_user include/net/sock.h:1511 [inline]
>>>>>> RIP: 0010:strp_data_ready+0x2b7/0x390 net/strparser/strparser.c:404
>>>>>> RSP: 0018:ffff8801db206b18 EFLAGS: 00010206
>>>>>> RAX: ffff8801d1e02080 RBX: ffff8801dad74c48 RCX: 0000000000000000
>>>>>> RDX: 0000000000000100 RSI: ffff8801d29fa0a0 RDI: ffffffff85cbede0
>>>>>> RBP: ffff8801db206b38 R08: 0000000000000005 R09: 1ffffffff0ce0bcd
>>>>>> R10: ffff8801db206a00 R11: dffffc0000000000 R12: ffff8801d29fa000
>>>>>> R13: ffff8801dad74c50 R14: ffff8801d4350a92 R15: 0000000000000001
>>>>>>  psock_data_ready+0x56/0x70 net/kcm/kcmsock.c:353
>>>>>
>>>>> Looks like KCM is calling sk_data_ready() without first taking the
>>>>> sock lock.
>>>>>
>>>>> /* Called with lower sock held */
>>>>> static void kcm_rcv_strparser(struct strparser *strp, struct sk_buff *skb)
>>>>> {
>>>>>  [...]
>>>>>         if (kcm_queue_rcv_skb(&kcm->sk, skb)) {
>>>>>
>>>>> In this case kcm->sk is not the same lock the comment is referring to.
>>>>> And kcm_queue_rcv_skb() will eventually call sk_data_ready().
>>>>>
>>>>> @Tom, how about wrapping the sk_data_ready call in {lock|release}_sock?
>>>>> I don't have anything better in mind immediately.
>>>>>
>>>> The sock locks are taken in reverse order in the send path so so
>>>> grabbing kcm sock lock with lower lock held to call sk_data_ready may
>>>> lead to deadlock like I think.
>>>>
>>>> It might be possible to change the order in the send path to do this.
>>>> Something like:
>>>>
>>>> trylock on lower socket lock
>>>> -if trylock fails
>>>>   - release kcm sock lock
>>>>   - lock lower sock
>>>>   - lock kcm sock
>>>> - call sendpage locked function
>>>>
>>>> I admit that dealing with two levels of socket locks in the data path
>>>> is quite a pain :-)
>>>
>>> up
>>>
>>> still happening and we've lost 50K+ test VMs on this
>>
>> up
>>
>> Still happens and number of crashes crossed 60K, can we do something
>> with this please?