netdev - Re: Asterisk deadlocks since Kernel 4.1

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Date:	Wed, 18 Nov 2015 22:23:49 +0100
From:	Stefan Priebe <s.priebe@...fihost.ag>
To:	Florian Weimer <fweimer@...hat.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>, netdev@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Asterisk deadlocks since Kernel 4.1


Am 18.11.2015 um 22:18 schrieb Florian Weimer:
> On 11/18/2015 09:23 PM, Stefan Priebe wrote:
>>
>> Am 17.11.2015 um 20:43 schrieb Thomas Gleixner:
>>> On Tue, 17 Nov 2015, Stefan Priebe wrote:
>>>> I've now also two gdb backtraces from two crashes:
>>>> http://pastebin.com/raw.php?i=yih5jNt8
>>>>
>>>> http://pastebin.com/raw.php?i=kGEcvH4T
>>>
>>> They don't tell me anything as I have no idea of the inner workings of
>>> asterisk. You might be better of to talk to the asterisk folks to help
>>> you track down what that thing is waiting for, so we can actually look
>>> at a well defined area.
>>
>> The asterisk guys told me it's a livelock asterisk is waiting for
>> getaddrinfo / recvmsg.
>>
>> Thread 2 (Thread 0x7fbe989c6700 (LWP 12890)):
>> #0  0x00007fbeb9eb487d in recvmsg () from /lib/x86_64-linux-gnu/libc.so.6
>> #1  0x00007fbeb9ed4fcc in ?? () from /lib/x86_64-linux-gnu/libc.so.6
>> #2  0x00007fbeb9ed544a in ?? () from /lib/x86_64-linux-gnu/libc.so.6
>> #3  0x00007fbeb9e92007 in getaddrinfo () from
>> /lib/x86_64-linux-gnu/libc.so.6
>
> Stefan,
>
> please try to get a backtrace with debugging information.  It is likely
> that this is the make_request/__check_pf functionality in glibc, but it
> would be nice to get some certainty.
>
> Which glibc version do you use?  Has it got a fix for CVE-2013-7423?

It's Debians 2.13-38+deb7u8 Debians issue tracker says it is fixed: 
https://security-tracker.debian.org/tracker/CVE-2013-7423

> So far, the only known cause for a hang in this place (that is, lack of
> return from recvmsg) is incorrect file descriptor use.  (CVE-2013-7423
> is such an issue in glibc itself.)  The kernel upgrade could change
> scheduling behavior, and the actual bug might have been latent before.
>
> Theoretically, recvmsg could also hang if the Netlink query was dropped
> by the kernel, or the final packet in the response was dropped.  We
> never saw that happen, even under extreme load, but I didn't test with
> recent kernels.

The load is very low in this system. Just 30 phones and only 1-6 calling.

> The glibc change Hannes mentioned won't detect the hang, but if there is
> incorrect file descriptor reuse going on, it is possible that the new
> assert catches it.
>
> Florian
>


Stefan
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