From: Florian Westphal <fw@xxxxxxxxx> commit a504b703bb1da526a01593da0e4be2af9d9f5fa8 upstream. 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@xxxxxxxxx> Signed-off-by: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- net/netfilter/nf_nat_proto_common.c | 29 +++++++++++++++++++++++------ 1 file changed, 23 insertions(+), 6 deletions(-) --- 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 s 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 s 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); Patches currently in stable-queue which might be from fw@xxxxxxxxx are queue-4.9/netfilter-nat-limit-port-clash-resolution-attempts.patch queue-4.9/netfilter-nat-remove-l4-protocol-port-rovers.patch