netdev - Re: ip6_dst_lookup

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Message-ID: <20130118124809.GA15977@hmsreliant.think-freely.org>
Date:	Fri, 18 Jan 2013 07:48:09 -0500
From:	Neil Horman <nhorman@...driver.com>
To:	Dave Jones <davej@...hat.com>
Cc:	netdev@...r.kernel.org
Subject: Re: ip6_dst_lookup_tail oops

On Thu, Jan 17, 2013 at 10:25:04AM -0500, Dave Jones wrote:
> On Wed, Jan 16, 2013 at 09:55:07AM -0500, Dave Jones wrote:
> 
>  > BUG: unable to handle kernel NULL pointer dereference at 000000000000017e
>  > IP: [<ffffffff81626308>] ip6_dst_lookup_tail+0xe8/0x200
>  > RIP: 0010:[<ffffffff81626308>]  [<ffffffff81626308>] ip6_dst_lookup_tail+0xe8/0x200
>  > RAX: 0000000000000011 RBX: 0000000000000000 RCX: 0000000000000000
>  > ..
>  > Call Trace:
>  >  [<ffffffff816266cb>] ip6_sk_dst_lookup_flow+0xcb/0x1b0
>  >  [<ffffffff8164803e>] udpv6_sendmsg+0x66e/0xb80
>  >  [<ffffffff815e6391>] inet_sendmsg+0x111/0x220
>  >  [<ffffffff81547220>] sock_sendmsg+0xb0/0xe0
>  >  [<ffffffff815486bc>] __sys_sendmsg+0x3ac/0x3c0
>  >  [<ffffffff8154afb9>] sys_sendmsg+0x49/0x90
>  >  [<ffffffff816a6802>] system_call_fastpath+0x16/0x1b
>  > 
>  >    0:	f6 80 6d 01 00 00 de 	testb  $0xde,0x16d(%rax)
>  >    7:	75 b9                	jne    0xffffffffffffffc2
>  >    9:	48 8b 56 18          	mov    0x18(%rsi),%rdx
>  >    d:	49 8d 75 24          	lea    0x24(%r13),%rsi
>  >   11:	b9                   	.byte 0xb9
>  >   12:	01 00                	add    %eax,(%rax)
>  > 	...
>  > 
>  > This looks like the GPF in this function I reported last September.
>  > http://www.spinics.net/lists/netdev/msg211894.html
>  > 
>  > In those reports, I ended up with an rt->n == 0x8000000000000011,
>  > but this time, it's just 0x11.
> 
> Now I've hit it with rt->n = 2000000000000010. So I'm starting to
> think this is getting passed in directly from userspace somehow, as
> these values look like the output of my 'set a few random bits' routine
> that sometimes gets called for params.
> 
> I'm having trouble mapping a corrupt sendmsg parameter to a messed up rt->n though.
> 
> Any clues ?
> 
> 	Dave
> 
Well, neighbor table entries for ipv6 get added over rtnetlink, but it seems you
would have to be able to memory map the socket to get a pointer like that into
place.  Trinity doesn't record the syscalls it makes does it?  That might be
helpful in tracking this down.
Neil

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