Re: [PATCH] af_packet: prevent information leak

[Eric Dumazet <eric.dumazet@gmail.com>]

Le lundi 06 juin 2011 à 22:24 -0700, David Miller a écrit :
> From: Eric Dumazet <eric.dumazet@gmail.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@gmail.com>
> > CC: Patrick McHardy <kaber@trash.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 ;)