Commit 946f9eb2 authored May 20, 2015 by Eric Dumazet Committed by David S. Miller May 21, 2015

tcp: improve REUSEADDR/NOREUSEADDR cohabitation



inet_csk_get_port() randomization effort tends to spread
sockets on all the available range (ip_local_port_range)

This is unfortunate because SO_REUSEADDR sockets have
less requirements than non SO_REUSEADDR ones.

If an application uses SO_REUSEADDR hint, it is to try to
allow source ports being shared.

So instead of picking a random port number in ip_local_port_range,
lets try first in first half of the range.

This gives more chances to use upper half of the range for the
sockets with strong requirements (not using SO_REUSEADDR)

Note this patch does not add a new sysctl, and only changes
the way we try to pick port number.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Marcelo Ricardo Leitner <mleitner@redhat.com>
Cc: Flavio Leitner <fbl@redhat.com>
Acked-by: Flavio Leitner <fbl@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent f5af1f57

net/ipv4/inet_connection_sock.c

+14 −0

Original line number	Diff line number	Diff line
		@@ -99,6 +99,7 @@ int inet_csk_get_port(struct sock *sk, unsigned short snum)
		struct net *net = sock_net(sk);
		int smallest_size = -1, smallest_rover;
		kuid_t uid = sock_i_uid(sk);
		int attempt_half = (sk->sk_reuse == SK_CAN_REUSE) ? 1 : 0;

		local_bh_disable();
		if (!snum) {
		@@ -106,6 +107,14 @@ int inet_csk_get_port(struct sock *sk, unsigned short snum)

		again:
		inet_get_local_port_range(net, &low, &high);
		if (attempt_half) {
		int half = low + ((high - low) >> 1);

		if (attempt_half == 1)
		high = half;
		else
		low = half;
		}
		remaining = (high - low) + 1;
		smallest_rover = rover = prandom_u32() % remaining + low;

		@@ -154,6 +163,11 @@ int inet_csk_get_port(struct sock *sk, unsigned short snum)
		snum = smallest_rover;
		goto have_snum;
		}
		if (attempt_half == 1) {
		/* OK we now try the upper half of the range */
		attempt_half = 2;
		goto again;
		}
		goto fail;
		}
		/* OK, here is the one we will use. HEAD is