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

[David Miller <davem@davemloft.net>]

From: Hannes Frederic Sowa <hannes@stressinduktion.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@ssi.bg>
> Signed-off-by: Marcelo Leitner <mleitner@redhat.com>
> Signed-off-by: Florian Westphal <fw@strlen.de>
> Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>

Applied and queued up for -stable, thanks.