netdev - Re: AW: AW: PROBLEM: Kernel Oops in UDP stack

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Date:   Wed, 01 Aug 2018 12:44:22 +0200
From:   Paolo Abeni <pabeni@...hat.com>
To:     Marcel Hellwig <mhellwig@...-group.com>,
        'Eric Dumazet' <eric.dumazet@...il.com>,
        "'davem@...emloft.net'" <davem@...emloft.net>,
        "'kuznet@....inr.ac.ru'" <kuznet@....inr.ac.ru>,
        "'yoshfuji@...ux-ipv6.org'" <yoshfuji@...ux-ipv6.org>,
        "'andrew@...n.ch'" <andrew@...n.ch>
Cc:     "'netdev@...r.kernel.org'" <netdev@...r.kernel.org>,
        "'linux-kernel@...r.kernel.org'" <linux-kernel@...r.kernel.org>,
        Matthias Wystrik <mwystrik@...-group.com>
Subject: Re: AW: AW: PROBLEM: Kernel Oops in UDP stack

On Wed, 2018-08-01 at 10:35 +0000, Marcel Hellwig wrote:
> > > [<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]

I *think* pskb_trim_rcsum() in __udp4_lib_rcv() can copy the ipv4
header to an unaligned address, for cloned skbs. If I understood
correctly the relevant socket is a mcast one, so cloned skbs can land
there.

Paolo