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 <eduma...@google.com>
Cc: Marcelo Ricardo Leitner <mleit...@redhat.com>
Cc: Flavio Leitner <f...@redhat.com>
---
net/ipv4/inet_connection_sock.c | 14 ++++++++++++++
1 file changed, 14 insertions(+)
diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index b95fb263a13f..60021d0d9326 100644
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c
@@ -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 @@ again:
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
--
2.2.0.rc0.207.ga3a616c
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