Re: [Qemu-devel] [PATCH] slirp: Don't crash on packets from 0.0.0.0/8.

[Jan Kiszka]

On 2012-11-12 15:41, Nickolai Zeldovich wrote:
> On Mon, Nov 12, 2012 at 4:37 AM, Jan Kiszka <address@hidden> wrote:
>> On 2012-11-12 01:59, Nickolai Zeldovich wrote:
>>> LWIP can generate packets with a source of 0.0.0.0, which triggers an
>>> assertion failure in arp_table_add().  Instead of crashing, simply return
>>> to avoid adding an invalid ARP table entry.
>>
>> I would prefer to filter out such invalid packets at a different level.
>> Did you analyzed which path it takes through the stack?
> 
> The particular packet that crashed qemu for me was a gratuitous ARP,
> though it looks like all three calls to arp_table_add() in arp_input()
> can trigger this.
> 
> Popping up one level, I'm not sure why arp_table_add() and
> arp_table_search() need a special case for 0.0.0.0/8 in the first
> place.  I couldn't find any other code that assumes the ARP table
> cannot contain 0.0.0.0/8 entries.  Would anything break if the check
> for 0.0.0.0/8 was removed from arp_table_add() and arp_table_search()
> altogether?

0.0.0.0/8 are source-only, invalid as destination. So they have no place
in the ARP table.

OK, let's follow your path and filter them in arp_table_add. Just add
the missing braces and resend.

Jan

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