[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>

include/net/inet_hashtables.h

@@ -125,9 +125,7 @@ struct inet_hashinfo {
 	rwlock_t			lhash_lock ____cacheline_aligned;
 	atomic_t			lhash_users;
 	wait_queue_head_t		lhash_wait;
-	spinlock_t			portalloc_lock;
 	kmem_cache_t			*bind_bucket_cachep;
-	int				port_rover;
 };
 
 static inline unsigned int inet_ehashfn(const __u32 laddr, const __u16 lport,

net/dccp/ipv4.c

@@ -31,8 +31,6 @@ struct inet_hashinfo __cacheline_aligned dccp_hashinfo = {
 	.lhash_lock	= RW_LOCK_UNLOCKED,
 	.lhash_users	= ATOMIC_INIT(0),
 	.lhash_wait = __WAIT_QUEUE_HEAD_INITIALIZER(dccp_hashinfo.lhash_wait),
-	.portalloc_lock	= SPIN_LOCK_UNLOCKED,
-	.port_rover	= 1024 - 1,
 };
 
 EXPORT_SYMBOL_GPL(dccp_hashinfo);
@@ -125,36 +123,15 @@ static int dccp_v4_hash_connect(struct sock *sk)
 	int ret;
 
  	if (snum == 0) {
- 		int rover;
  		int low = sysctl_local_port_range[0];
  		int high = sysctl_local_port_range[1];
  		int remaining = (high - low) + 1;
+ 		int rover = net_random() % (high - low) + low;
 		struct hlist_node *node;
  		struct inet_timewait_sock *tw = NULL;
 
  		local_bh_disable();
-
- 		/* TODO. Actually it is not so bad idea to remove
- 		 * dccp_hashinfo.portalloc_lock before next submission to
-		 * Linus.
- 		 * As soon as we touch this place at all it is time to think.
- 		 *
- 		 * Now it protects single _advisory_ variable
-		 * dccp_hashinfo.port_rover, hence it is mostly useless.
- 		 * Code will work nicely if we just delete it, but
- 		 * I am afraid in contented case it will work not better or
- 		 * even worse: another cpu just will hit the same bucket
- 		 * and spin there.
- 		 * So some cpu salt could remove both contention and
- 		 * memory pingpong. Any ideas how to do this in a nice way?
- 		 */
- 		spin_lock(&dccp_hashinfo.portalloc_lock);
- 		rover = dccp_hashinfo.port_rover;
-
  		do {
- 			rover++;
- 			if ((rover < low) || (rover > high))
- 				rover = low;
  			head = &dccp_hashinfo.bhash[inet_bhashfn(rover,
 						    dccp_hashinfo.bhash_size)];
  			spin_lock(&head->lock);
@@ -187,9 +164,9 @@ static int dccp_v4_hash_connect(struct sock *sk)
 
  		next_port:
  			spin_unlock(&head->lock);
+ 			if (++rover > high)
+ 				rover = low;
  		} while (--remaining > 0);
- 		dccp_hashinfo.port_rover = rover;
- 		spin_unlock(&dccp_hashinfo.portalloc_lock);
 
  		local_bh_enable();
 
@@ -197,9 +174,6 @@ static int dccp_v4_hash_connect(struct sock *sk)
 
 ok:
  		/* All locks still held and bhs disabled */
- 		dccp_hashinfo.port_rover = rover;
- 		spin_unlock(&dccp_hashinfo.portalloc_lock);
-
  		inet_bind_hash(sk, tb, rover);
 		if (sk_unhashed(sk)) {
  			inet_sk(sk)->sport = htons(rover);

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

net/ipv4/tcp.c

@@ -2112,7 +2112,6 @@ void __init tcp_init(void)
 		sysctl_tcp_max_orphans >>= (3 - order);
 		sysctl_max_syn_backlog = 128;
 	}
-	tcp_hashinfo.port_rover = sysctl_local_port_range[0] - 1;
 
 	sysctl_tcp_mem[0] =  768 << order;
 	sysctl_tcp_mem[1] = 1024 << order;

net/ipv4/tcp_ipv4.c

@@ -93,8 +93,6 @@ struct inet_hashinfo __cacheline_aligned tcp_hashinfo = {
 	.lhash_lock	= RW_LOCK_UNLOCKED,
 	.lhash_users	= ATOMIC_INIT(0),
 	.lhash_wait	= __WAIT_QUEUE_HEAD_INITIALIZER(tcp_hashinfo.lhash_wait),
-	.portalloc_lock	= SPIN_LOCK_UNLOCKED,
-	.port_rover	= 1024 - 1,
 };
 
 static int tcp_v4_get_port(struct sock *sk, unsigned short snum)

net/ipv6/tcp_ipv6.c

@@ -114,16 +114,9 @@ static int tcp_v6_get_port(struct sock *sk, unsigned short snum)
 		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(&tcp_hashinfo.portalloc_lock);
-		if (tcp_hashinfo.port_rover < low)
-			rover = low;
-		else
-			rover = tcp_hashinfo.port_rover;
-		do {	rover++;
-			if (rover > high)
-				rover = low;
+		do {
 			head = &tcp_hashinfo.bhash[inet_bhashfn(rover, tcp_hashinfo.bhash_size)];
 			spin_lock(&head->lock);
 			inet_bind_bucket_for_each(tb, node, &head->chain)
@@ -132,9 +125,9 @@ static int tcp_v6_get_port(struct sock *sk, unsigned short snum)
 			break;
 		next:
 			spin_unlock(&head->lock);
+			if (++rover > high)
+				rover = low;
 		} while (--remaining > 0);
-		tcp_hashinfo.port_rover = rover;
-		spin_unlock(&tcp_hashinfo.portalloc_lock);
 
 		/* Exhausted local port range during search?  It is not
 		 * possible for us to be holding one of the bind hash