Re: [PATCH net-next] ipv4: tcp: dont cache unconfirmed intput dst

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From: Eric Dumazet <eric.dumazet@xxxxxxxxx>
Date: Wed, 27 Jun 2012 11:14:15 +0200

> From: Eric Dumazet <edumazet@xxxxxxxxxx>
> 
> DDOS synflood attacks hit badly IP route cache.
> 
> On typical machines, this cache is allowed to hold up to 8 Millions dst
> entries, 256 bytes for each, for a total of 2GB of memory.
> 
> rt_garbage_collect() triggers and tries to cleanup things.
> 
> Eventually route cache is disabled but machine is under fire and might
> OOM and crash.
> 
> This patch exploits the new TCP early demux, to set a nocache
> boolean in case incoming TCP frame is for a not yet ESTABLISHED or
> TIMEWAIT socket.
> 
> This 'nocache' boolean is then used in case dst entry is not found in
> route cache, to create an unhashed dst entry (DST_NOCACHE)
> 
> SYN-cookie-ACK sent use a similar mechanism (ipv4: tcp: dont cache
> output dst for syncookies), so after this patch, a machine is able to
> absorb a DDOS synflood attack without polluting its IP route cache.
> 
> Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>

Applied, thanks Eric.
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