[TCP/DCCP]: Randomize port selection

This patch randomizes the port selected on bind() for connections
to help with possible security attacks. It should also be faster
in most cases because there is no need for a global lock.

Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>

1 files changed, 3 insertions, 11 deletions

diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index 94468a76c5b4..3fe021f1a566 100644
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c
@@ -78,17 +78,9 @@ int inet_csk_get_port(struct inet_hashinfo *hashinfo,
                 int low = sysctl_local_port_range[0];
                 int high = sysctl_local_port_range[1];
                 int remaining = (high - low) + 1;
-                int rover;
+                int rover = net_random() % (high - low) + low;
 
-                spin_lock(&hashinfo->portalloc_lock);
-                if (hashinfo->port_rover < low)
-                        rover = low;
-                else
-                        rover = hashinfo->port_rover;
                 do {
-                        rover++;
-                        if (rover > high)
-                                rover = low;
                         head = &hashinfo->bhash[inet_bhashfn(rover, hashinfo->bhash_size)];
                         spin_lock(&head->lock);
                         inet_bind_bucket_for_each(tb, node, &head->chain)
@@ -97,9 +89,9 @@ int inet_csk_get_port(struct inet_hashinfo *hashinfo,
                         break;
                 next:
                         spin_unlock(&head->lock);
+                        if (++rover > high)
+                                rover = low;
                 } while (--remaining > 0);
-                hashinfo->port_rover = rover;
-                spin_unlock(&hashinfo->portalloc_lock);
 
                 /* Exhausted local port range during search?  It is not
                  * possible for us to be holding one of the bind hash