Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: AW: PROBLEM: Kernel Oops in UDP stack
To:     David Laight <David.Laight@ACULAB.COM>,
        'Marcel Hellwig' <mhellwig@mut-group.com>,
        'Eric Dumazet' <eric.dumazet@gmail.com>,
        "'davem@davemloft.net'" <davem@davemloft.net>,
        "'kuznet@ms2.inr.ac.ru'" <kuznet@ms2.inr.ac.ru>,
        "'yoshfuji@linux-ipv6.org'" <yoshfuji@linux-ipv6.org>,
        "'andrew@lunn.ch'" <andrew@lunn.ch>
Cc:     "'netdev@vger.kernel.org'" <netdev@vger.kernel.org>,
        "'linux-kernel@vger.kernel.org'" <linux-kernel@vger.kernel.org>,
        Matthias Wystrik <mwystrik@mut-group.com>
References: <18092446dfa7435aaa8deaab65afbf23@ZCOM03.mut-group.com>
 <f1940127-7307-e1ba-7a05-075680a6d3c1@gmail.com>
 <b8ceab2531f345d295686903b003787b@ZCOM03.mut-group.com>
 <96753ca4-88fe-aa26-b439-6e22eaf8b524@gmail.com>
 <9f9d731107594b368504cbbaf698bc3d@ZCOM03.mut-group.com>
 <d16f03bf47b24313ad9f2ff4e37d6274@AcuMS.aculab.com>
From:   Eric Dumazet <eric.dumazet@gmail.com>
Message-ID: <405319c1-2fa0-e1b5-7173-b19d9769d98a@gmail.com>
Date:   Thu, 2 Aug 2018 06:13:02 -0700
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101
 Thunderbird/52.6.0
MIME-Version: 1.0
In-Reply-To: <d16f03bf47b24313ad9f2ff4e37d6274@AcuMS.aculab.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


On 08/02/2018 02:17 AM, David Laight wrote:
> From: Marcel Hellwig
>> Sent: 01 August 2018 11:36
>>>> [<c0228adc>] (udp_recvmsg+0x284/0x33c) from [<c02306e0>] (inet_recvmsg+0x38/0x4c):
>> net/ipv4/udp.c:1234
>>>
>>>              sin->sin_addr.s_addr = ip_hdr(skb)->saddr;
>>>
>>> Unaligned access trap (virtual address c14fe63a), so either sin or ip_hdr(skb) are not on a 32bit
>> alignment
>>>
>>> Can you produce the disassembly of the trapping instruction ?
>>
>> https://gist.github.com/hellow554/6b11c6c0827d5db80a7e66f71f5636ff#file-net_uipv4_udp-lst-L1892-L1895
>>
>> 		sin->sin_addr.s_addr = ip_hdr(skb)->saddr;
>> c0228ad8:	e5943080 	ldr	r3, [r4, #128]	; 0x80
>> c0228adc:	e593300c 	ldr	r3, [r3, #12]
>> c0228ae0: 	e5823004	str	r3, [r2, #4]
> 
> There are actually 2 faults, difficult to quickly sort out the merged tracebacks.
> You are also running a rather old kernel: Linux version 3.4.113.
> 
> It may well be that whichever ethernet driver generated the misaligned frame
> has since been fixed.

A misalign frame driver problem would have faulted earlier in IP stack,
much before we perform the copy to user space in udp_recvmsg()