netdev - Re: PROBLEM: raw sockets rewriting IP ID in rare cases.

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Date:	Sun, 15 Aug 2010 13:57:41 -0400
From:	Morgon.J.Kanter@...tmouth.edu
To:	David Miller <davem@...emloft.net>
Cc:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: PROBLEM: raw sockets rewriting IP ID in rare cases.

Quoting David Miller <davem@...emloft.net>:
>> I have stumbled across what I think is a rare bug in the raw socket  
>>  mechanism
>> of the kernel. When attempting to send a certain packet with an IP   
>> ID of zero
>> from a raw socket created with the call "socket(AF_INET, SOCK_RAW,
>> IPPROTO_RAW)", the kernel will modify the IP ID field and update   
>> the checksum.
>> It only seems to do it with this specific packet for some reason, similar
>> packets with an IP ID of zero do not get so mangled.
>
> Even when using hdrinclude mode of RAW ipv4 sockets, if you specify
> a zero ID field, the kernel will fill it in with the usual value.
>
> It is expected behavior.
>
> If you want the kernel to leave your ID field alone, provide a
> non-zero one.

Is there a way to turn this behavior off, then, with raw sockets? Zero  
is the desired ID value.

Thanks,
-- Morgon
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