netdev - Re: [PATCH v3 net] ip: make IP identifiers less predictable

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Date:	Mon, 28 Jul 2014 18:47:00 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	netdev@...r.kernel.org, jeffk@...unm.edu, crandall@...unm.edu,
	torvalds@...ux-foundation.org, w@....eu, security@...nel.org,
	hannes@...hat.com
Subject: Re: [PATCH v3 net] ip: make IP identifiers less predictable

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Sat, 26 Jul 2014 08:58:10 +0200

> From: Eric Dumazet <edumazet@...gle.com>
> 
> In "Counting Packets Sent Between Arbitrary Internet Hosts", Jeffrey and
> Jedidiah describe ways exploiting linux IP identifier generation to
> infer whether two machines are exchanging packets.
> 
> With commit 73f156a6e8c1 ("inetpeer: get rid of ip_id_count"), we
> changed IP id generation, but this does not really prevent this
> side-channel technique.
> 
> This patch adds a random amount of perturbation so that IP identifiers
> for a given destination [1] are no longer monotonically increasing after
> an idle period.
> 
> Note that prandom_u32_max(1) returns 0, so if generator is used at most
> once per jiffy, this patch inserts no hole in the ID suite and do not
> increase collision probability.
> 
> This is jiffies based, so in the worst case (HZ=1000), the id can
> rollover after ~65 seconds of idle time, which should be fine.
> 
> We also change the hash used in __ip_select_ident() to not only hash
> on daddr, but also saddr and protocol, so that ICMP probes can not be
> used to infer information for other protocols.
> 
> For IPv6, adds saddr into the hash as well, but not nexthdr.
> 
> If I ping the patched target, we can see ID are now hard to predict.
 ...
> [1] TCP sessions uses a per flow ID generator not changed by this patch.
> 
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Reported-by: Jeffrey Knockel <jeffk@...unm.edu>
> Reported-by: Jedidiah R. Crandall <crandall@...unm.edu>

Applied and queued up for -stable, thanks everyone.
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