netdev - Re: [RFC] sctp/tcp: Question -- ICMPv4 length check (not) redundant?

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Message-ID: <20080729015649.GA15441@gondor.apana.org.au>
Date:	Tue, 29 Jul 2008 09:56:49 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Vlad Yasevich <vladislav.yasevich@...com>
Cc:	Gerrit Renker <gerrit@....abdn.ac.uk>,
	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [RFC] sctp/tcp: Question -- ICMPv4 length check (not) redundant?

On Mon, Jul 28, 2008 at 01:27:46PM -0400, Vlad Yasevich wrote:
> 
> So the suggestion really is then to remove the length check icmp_unreach()?

Yes.

> Because as it stands right now, the protocol error handler will not be invoked
> if we don't have the iphdr + 8 bytes worth of data.  That's is actually a requirement
> from the ICMP rfc 792.

That requirement only makes sense if the original packet has at
least 8 bytes of payload.  Since the RFC doesn't talk about
padding in case it doesn't have 8 byte, the behaviour in that
case is clearly undefined.

As far as Linux is concerned, we've never done padding if there
is less than 8 bytes of payload.  So as such we must be prepared
to deal with that on the input side as well.

Cheers,
-- 
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Email: Herbert Xu ~{PmV>HI~} <herbert@...dor.apana.org.au>
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