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Date:   Wed, 6 Dec 2017 16:44:10 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Tom Herbert <tom@...bertland.com>
Cc:     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, Tom Herbert <tom@...ntonium.net>,
        Cong Wang <xiyou.wangcong@...il.com>
Subject: Re: WARNING in strp_data_ready

On Mon, Oct 30, 2017 at 11:06 PM, Tom Herbert <tom@...bertland.com> wrote:
> On Mon, Oct 30, 2017 at 2:44 PM, John Fastabend
> <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

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