netdev - Re: [PATCH] IPv4: skip loopback checksums in ip

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Message-ID: <4ADCD5E1.7060400@gmail.com>
Date:	Mon, 19 Oct 2009 23:10:57 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Torsten Schmidt <torsten.schmidt@...06.tu-chemnitz.de>
CC:	Linux Netdev List <netdev@...r.kernel.org>
Subject: Re: [PATCH] IPv4: skip loopback checksums in ip_rcv()

Torsten Schmidt a écrit :
> Eric Dumazet wrotes:
>> This is bogus IMHO.
>>
>> One bit could be corrupted in iph, and ntohl(iph->daddr) becomes 0x7fxxyyzz,
>> we then accept a bogus frame. This is a RFC violation.
>>
>> This also slows down non loopback devices, adding an extra test.
>>
>> ip_fast_csum() is really fast (about 16 instructions).
> 
> Yes, you are right. So it would be better to only skip csum if *dev is 
> our loopback interface ? Right ?

An application could send a bogus IP packet using RAW interface, and we still should
check IP checksum before delivering this packet, even on loopback device.

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