Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1753824AbaLASIn (ORCPT <rfc822;w@1wt.eu>);
	Mon, 1 Dec 2014 13:08:43 -0500
Received: from mx1.redhat.com ([209.132.183.28]:60314 "EHLO mx1.redhat.com"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1753330AbaLASIl (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Mon, 1 Dec 2014 13:08:41 -0500
Message-ID: <547CAEA3.3090906@redhat.com>
Date: Mon, 01 Dec 2014 19:08:35 +0100
From: Daniel Borkmann <dborkman@redhat.com>
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/17.0 Thunderbird/17.0
MIME-Version: 1.0
To: =?UTF-8?B?Um9iZXJ0IMWad2nEmWNraQ==?= <robert@swiecki.net>
CC: linux-sctp@vger.kernel.org, linux-kernel@vger.kernel.org,
        vyasevich@gmail.com
Subject: Re: panic in skb_push via sctp
References: <CAP145pgZ2rbALf-Ce=uGc72DBCNXBvkrEPG43VUkSqkpiLuKsA@mail.gmail.com> <547CA719.6060101@redhat.com> <CAP145pggcEUKz3QhDEGdzWZDusPfwJsZ8juqjbRr+8g6RxuJfA@mail.gmail.com>
In-Reply-To: <CAP145pggcEUKz3QhDEGdzWZDusPfwJsZ8juqjbRr+8g6RxuJfA@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On 12/01/2014 07:02 PM, Robert Święcki wrote:
> Thanks for looking into it. I can try with your patch, but no
> guarantees that the fuzzer will hit the same condition in some
> reasonable time-frame. Will get back in some time with results.

Ok, thanks!

> PS. If you think it's possible to create a repro (userland code) which
> can trigger this, I can give it a try.

Did by accident trinity create tunnels? It looks that upper layer
protocols (except SCTP) all allocate and reserve MAX_HEADER to
accommodate enough head room in worst case for possible tunnels.

> 2014-12-01 18:36 GMT+01:00 Daniel Borkmann <dborkman@redhat.com>:
>> On 12/01/2014 05:49 PM, Robert Święcki wrote:
>>>
>>> I don't have much more, cause my kernel is kASLRNized and gdb cannot
>>> handle that, but pasting output from kdb. Maybe somebody will be able
>>> to see something obvious.
>>>
>>>    <0>[93699.703244] skbuff: skb_under_panic: text:ffffffff83cff03e
>>> len:104 put:56 head:ffff8803bd804ec0 data:ffff8803bd804ebc tail:0x64
>>> end:0xc0 dev:<NULL>
>>
>>
>> Thanks for the report!
>>
>> On a first view, it looks like we should be using MAX_HEADER instead
>> of LL_MAX_HEADER here, could you try with the following patch:
>>
>> diff --git a/net/sctp/output.c b/net/sctp/output.c
>> index 42dffd4..fc5e45b 100644
>> --- a/net/sctp/output.c
>> +++ b/net/sctp/output.c
>> @@ -401,12 +401,12 @@ int sctp_packet_transmit(struct sctp_packet *packet)
>>          sk = chunk->skb->sk;
>>
>>          /* Allocate the new skb.  */
>> -       nskb = alloc_skb(packet->size + LL_MAX_HEADER, GFP_ATOMIC);
>> +       nskb = alloc_skb(packet->size + MAX_HEADER, GFP_ATOMIC);
>>          if (!nskb)
>>                  goto nomem;
>>
>>          /* Make sure the outbound skb has enough header room reserved. */
>> -       skb_reserve(nskb, packet->overhead + LL_MAX_HEADER);
>> +       skb_reserve(nskb, packet->overhead + MAX_HEADER);
>>
>>          /* Set the owning socket so that we know where to get the
>>           * destination IP address.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/