Subject: Re: oops in net/ipv4/icmp.c:icmp_send() with icmp_errors_use_inbound_ifaddr (fwd)

From: Patrick McHardy <[email-masked]>
Date: Mon, 14 May 2007 20:46:29 +0200

James Morris wrote:
> ---------- Forwarded message ----------
> Date: Mon, 14 May 2007 08:15:50 -0700 (PDT)
> From: Curtis Doty <[email-masked]>
> To: Linux Kernel <[email-masked]>
> Subject: oops in net/ipv4/icmp.c:icmp_send() with icmp_errors_use_inbound_ifaddr
> 
> Summary: On a multi-homed box, after turning on
> /proc/sys/net/ipv4/icmp_errors_use_inbound_ifaddr, it now periodically oopses
> when trying to lookup the source address to use for sending an ICMP in response
> to a jump ipt_REJECT.
> 
> I'm still trying to figure out what makes this test case unique. It spuriously
> occurs with many fedora builds of 2.6.{18,19,20} all of which don't appear to
> have any patches in this area of the kernel. Just _maybe_ it's because of a
> combination of dogleg routing and overloading one vlan with multiple subnets:
> 
> [..]
> 
> BUG: unable to handle kernel NULL pointer dereference at virtual address
> 000000a8
> [...]
> EIP is at inet_select_addr+0x4/0x9f
> eax: 00000000   ebx: f8b97046   ecx: 000000fd   edx: 00000000
> esi: 000000fd   edi: 00000001   ebp: f71cd0ac   esp: c078bc9c
> ds: 007b   es: 007b   ss: 0068
> Process swapper (pid: 0, ti=c078b000 task=c06fc480 task.ti=c0746000)
> Stack: f8b97046 f601b130 c05fd0b6 f728b980 f728b980 f8b5adbb c05bcb6e c078bd74
>        00000003 00000003 00000246 00000246 00000000 f887e014 f8a611a6 f7c1ea80
>        f728b9a8 00000000 f727d220 f887e000 00000001 00000072 f7383800 f728b980
> Call Trace:
>  [<f8b97046>] reject+0x0/0x4ae [ipt_REJECT]
>  [<c05fd0b6>] icmp_send+0x14d/0x39b

A REJECT target in the output chain will trigger this in combination
with icmp_errors_use_inbound_ifaddr because skb->dev is still NULL
at this point and its passed to inet_select_addr.

I'll look into this.