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SubjectRe: WARNING in strp_data_ready
On Wed, Dec 27, 2017 at 9:08 PM, Ozgur <ozgur@goosey.org> wrote:
>
>
> 27.12.2017, 22:21, "Dmitry Vyukov" <dvyukov@google.com>:
>> On Wed, Dec 27, 2017 at 8:09 PM, Tom Herbert <tom@herbertland.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@google.com> wrote:
>>>> On Wed, Dec 6, 2017 at 4:44 PM, Dmitry Vyukov <dvyukov@google.com> wrote:
>>>>>> <john.fastabend@gmail.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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