diff options
author | Florian Westphal <fw@strlen.de> | 2018-12-10 17:18:46 +0100 |
---|---|---|
committer | Pablo Neira Ayuso <pablo@netfilter.org> | 2018-12-17 23:32:08 +0100 |
commit | a504b703bb1da526a01593da0e4be2af9d9f5fa8 (patch) | |
tree | aac0ccf650669f9822080b7884020ff976afbcfe /net/netfilter | |
parent | b635cbf68ff35817d5a1634b0ade41f96ef70daf (diff) |
netfilter: nat: limit port clash resolution attempts
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>
Diffstat (limited to 'net/netfilter')
-rw-r--r-- | net/netfilter/nf_nat_proto_common.c | 29 |
1 files changed, 23 insertions, 6 deletions
diff --git a/net/netfilter/nf_nat_proto_common.c b/net/netfilter/nf_nat_proto_common.c index 136ab65c4082..dcb5d11688a1 100644 --- a/net/netfilter/nf_nat_proto_common.c +++ b/net/netfilter/nf_nat_proto_common.c @@ -40,9 +40,10 @@ void nf_nat_l4proto_unique_tuple(const struct nf_nat_l3proto *l3proto, enum nf_nat_manip_type maniptype, const struct nf_conn *ct) { - unsigned int range_size, min, max, i; + unsigned int range_size, min, max, i, attempts; __be16 *portptr; - u_int16_t off; + u16 off; + static const unsigned int max_attempts = 128; if (maniptype == NF_NAT_MANIP_SRC) portptr = &tuple->src.u.all; @@ -86,12 +87,28 @@ void nf_nat_l4proto_unique_tuple(const struct nf_nat_l3proto *l3proto, off = prandom_u32(); } - for (i = 0; ; ++off) { + attempts = range_size; + if (attempts > max_attempts) + attempts = max_attempts; + + /* We are in softirq; doing a search of the entire range risks + * soft lockup when all tuples are already used. + * + * If we can't find any free port from first offset, pick a new + * one and try again, with ever smaller search window. + */ +another_round: + for (i = 0; i < attempts; i++, off++) { *portptr = htons(min + off % range_size); - if (++i != range_size && nf_nat_used_tuple(tuple, ct)) - continue; - return; + if (!nf_nat_used_tuple(tuple, ct)) + return; } + + if (attempts >= range_size || attempts < 16) + return; + attempts /= 2; + off = prandom_u32(); + goto another_round; } EXPORT_SYMBOL_GPL(nf_nat_l4proto_unique_tuple); |