netdev - Re: [PATCH] netfilter: xt

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Date:	Mon, 14 May 2012 20:28:52 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Hans Schillstrom <hans.schillstrom@...csson.com>
Cc:	Jan Engelhardt <jengelh@...i.de>,
	Pablo Neira Ayuso <pablo@...filter.org>,
	"kaber@...sh.net" <kaber@...sh.net>,
	"jengelh@...ozas.de" <jengelh@...ozas.de>,
	"netfilter-devel@...r.kernel.org" <netfilter-devel@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"dan.carpenter@...cle.com" <dan.carpenter@...cle.com>,
	"hans@...illstrom.com" <hans@...illstrom.com>
Subject: Re: [PATCH] netfilter: xt_HMARK: endian bugs

On Mon, 2012-05-14 at 19:51 +0200, Hans Schillstrom wrote:
> On Monday 14 May 2012 18:24:34 Eric Dumazet wrote:
> > On Mon, 2012-05-14 at 18:09 +0200, Hans Schillstrom wrote:
> > 
> > > This context can contain both le & be machines,
> > > so at least in hmark it make sense
> > 
> > Before jhash() and its shuffle ? What do you mean ?
> 
> I want that a Big endian machine should produce the same
> hash value independent of flow direction as a Little endian.
> 

So one machine can be both le and be ? at the same time ?

> OK, I missed ntohl() before calling jhash_3words()
> 
> Correct me if I'm wrong here (have no big endian machine available for test)
> jhash_3words() and __jhash_final() seems to be "endian" safe.
> 
> So by doing the expensive ntohl on addresses and ports into jhash_3words()
> it will produce the same value on both be and le.
> 

And what is the purpose of the jhash output ? Is is sent to other
machines on the network, or only localy used ?

> That's why I want to have the ntohs() / ntohl() when comparing.

If xt_HMARK depends on a particular bit ordering to jhash() input, then
something is really wrong. I mean it.

jhash() primary purpose it to shuffle input.

We use (__force u32) everywhere in network tree to avoid sparse
warnings. Please grep for them.



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