netfilter: nat: limit port clash resolution attempts

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In case almost or all available ports are taken, clash resolution can
take a very long time, resulting in soft lockup.

This can happen when many to-be-natted hosts connect to same
destination:port (e.g. a proxy) and all connections pass the same SNAT.

Pick a random offset in the acceptable range, then try ever smaller
number of adjacent port numbers, until either the limit is reached or a
useable port was found.  This results in at most 248 attempts
(128 + 64 + 32 + 16 + 8, i.e. 4 restarts with new search offset)
instead of 64000+,

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

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Florian Westphal 2018-12-10 17:18:46 +01:00 • committed by Pablo Neira Ayuso

parent b635cbf68f

commit a504b703bb

1 changed files with 23 additions and 6 deletions

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net/netfilter/nf_nat_proto_common.c

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