netdev - Re: [PATCH] netfilter: xt

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Message-ID: <201205141951.36692.hans.schillstrom@ericsson.com>
Date:	Mon, 14 May 2012 19:51:34 +0200
From:	Hans Schillstrom <hans.schillstrom@...csson.com>
To:	Eric Dumazet <eric.dumazet@...il.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 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.

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.

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

> 
> Please respin your patch using (__force u16/u32) instead of
> useless/expensive ntohs() / ntohl() (in _this_ context of hashing)
> 
> If you compare two 32bits values, of course they must have same
> ordering, but seeding jhash() is another matter.
> 
> (Granted all calls use the same ordering of course)
> 
> sparse is great tool, but if you add useless ntohl() calls to make
> sparse silent, then its probably better to not use sparse.
> 
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