Date:   Wed, 27 Dec 2017 21:14:21 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Ozgur <ozgur@...sey.org>
Cc:     Tom Herbert <tom@...bertland.com>,
        John Fastabend <john.fastabend@...il.com>,
        syzbot 
        <bot+c91c53af67f9ebe599a337d2e70950366153b295@...kaller.appspotmail.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Biggers <ebiggers@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        "syzkaller-bugs@...glegroups.com" <syzkaller-bugs@...glegroups.com>,
        Tom Herbert <tom@...ntonium.net>,
        Cong Wang <xiyou.wangcong@...il.com>
Subject: Re: WARNING in strp_data_ready

On Wed, Dec 27, 2017 at 9:08 PM, Ozgur <ozgur@...sey.org> wrote:
>
>
> 27.12.2017, 22:21, "Dmitry Vyukov" <dvyukov@...gle.com>:
>> On Wed, Dec 27, 2017 at 8:09 PM, Tom Herbert <tom@...bertland.com> wrote:
>>>  Did you try the patch I posted?
>>
>> Hi Tom,
>
> Hello Dmitry,
>
>> 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
>
> I think we need to fixed patch for crash, in fact check to patch code and test solve the bug.
> How do test it because there is no patch in the following bug?

Hi Ozgur,

I am not sure I completely understand what you mean. But the
reproducer for this bug (which one can use for testing) is here:
https://groups.google.com/forum/#!topic/syzkaller-bugs/Kxs05ziCpgY
Tom also mentions there is some patch for this, but I don't know where
it is, it doesn't seem to be referenced from this thread.


> The fix patch should be for this net/kcm/kcmsock.c file and  lock functions must be added calling sk_data_ready ().
> Regards
>
> Ozgur
>
>>>  On Wed, Dec 27, 2017 at 10:25 AM, Dmitry Vyukov <dvyukov@...gle.com> wrote:
>>>>  On Wed, Dec 6, 2017 at 4:44 PM, Dmitry Vyukov <dvyukov@...gle.com> wrote:
>>>>>>  <john.fastabend@...il.com> 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?

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