Re: WARNING in strp_data_ready

[Dmitry Vyukov]

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?