netdev - Re: [PATCH net v3] ipv4: try to cache dst_entries which would cause a redirect

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Message-Id: <20150126.172905.2265431683987062613.davem@davemloft.net>
Date:	Mon, 26 Jan 2015 17:29:05 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	hannes@...essinduktion.org
Cc:	netdev@...r.kernel.org, ja@....bg, mleitner@...hat.com,
	fw@...len.de
Subject: Re: [PATCH net v3] ipv4: try to cache dst_entries which would
 cause a redirect

From: Hannes Frederic Sowa <hannes@...essinduktion.org>
Date: Fri, 23 Jan 2015 12:01:26 +0100

> Not caching dst_entries which cause redirects could be exploited by hosts
> on the same subnet, causing a severe DoS attack. This effect aggravated
> since commit f88649721268999 ("ipv4: fix dst race in sk_dst_get()").
> 
> Lookups causing redirects will be allocated with DST_NOCACHE set which
> will force dst_release to free them via RCU.  Unfortunately waiting for
> RCU grace period just takes too long, we can end up with >1M dst_entries
> waiting to be released and the system will run OOM. rcuos threads cannot
> catch up under high softirq load.
> 
> Attaching the flag to emit a redirect later on to the specific skb allows
> us to cache those dst_entries thus reducing the pressure on allocation
> and deallocation.
> 
> This issue was discovered by Marcelo Leitner.
> 
> Cc: Julian Anastasov <ja@....bg>
> Signed-off-by: Marcelo Leitner <mleitner@...hat.com>
> Signed-off-by: Florian Westphal <fw@...len.de>
> Signed-off-by: Hannes Frederic Sowa <hannes@...essinduktion.org>

Applied and queued up for -stable, thanks.
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