netdev - Re: [PATCH] af_packet: prevent information leak

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Date:	Mon, 06 Jun 2011 22:42:44 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	netdev@...r.kernel.org, kaber@...sh.net
Subject: Re: [PATCH] af_packet: prevent information leak

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Tue, 07 Jun 2011 07:38:39 +0200

> Le lundi 06 juin 2011 à 22:24 -0700, David Miller a écrit :
>> From: Eric Dumazet <eric.dumazet@...il.com>
>> Date: Tue, 07 Jun 2011 07:02:19 +0200
>> 
>> > In 2.6.27, commit 393e52e33c6c2 (packet: deliver VLAN TCI to userspace)
>> > added a small information leak.
>> > 
>> > Add padding field and make sure its zeroed before copy to user.
>> > 
>> > Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
>> > CC: Patrick McHardy <kaber@...sh.net>
>> 
>> I fear this will change the size of these structures on some weird
>> architecture.  Doesn't ARM, for example, have weird rules
>> wrt. alignment and structure sizing when "smaller than word" elements
>> are involved?
>> 
>> That's why we need __packed on:
>> 
>> struct nd_opt_hdr {
>> 	__u8		nd_opt_type;
>> 	__u8		nd_opt_len;
>> } __packed;
>> 
>> for example.
>> 
>> Probably safe to just do a memset of the tail, and the constant length
>> will evaluate to zero on these weird platforms.  On others, where the
>> padding does matter, the memset will emit the same code as your new
>> assignments do.
> 
> It should not matter for these structures, or 393e52e33c6c2 would have
> break applications on all arches (not only ARM), since it enlarged them
> without any warning ;)

Indeed.  Ok, I'm convinced.

Applied and queued up for -stable, thanks!
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