netdev - Re: inet_hash_connect: source port allocation

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Date:	Mon, 29 Nov 2010 20:07:35 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	John Haxby <john.haxby@...cle.com>
Cc:	NetDev <netdev@...r.kernel.org>,
	Stephen Hemminger <shemminger@...tta.com>
Subject: Re: inet_hash_connect: source port allocation

Le lundi 29 novembre 2010 à 19:46 +0100, Eric Dumazet a écrit :
> Le lundi 29 novembre 2010 à 18:29 +0000, John Haxby a écrit :
> 
> > Sorry,  I think I phrased my question badly.
> > 
> > inet_csk_get_port() starts its search for a free port with
> > 
> >      smallest_rover = rover = net_random() % remaining + low;
> > 
> > whereas __inet_hash_connect() basically misses out that call to 
> > net_random() so you get a predictable port number.
> > 
> > Is there any good reason why that is the case?
> > 
> 
> It seems random select was done at bind() time only in commit
> 6df716340da3a6f ([TCP/DCCP]: Randomize port selection)
> 
> It probably should be done in autobind too.
> 
> 

I'll test following patch :

diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c
index 1b344f3..65c3702 100644
--- a/net/ipv4/inet_hashtables.c
+++ b/net/ipv4/inet_hashtables.c
@@ -466,20 +466,18 @@ int __inet_hash_connect(struct inet_timewait_death_row *death_row,
 	int twrefcnt = 1;
 
 	if (!snum) {
-		int i, remaining, low, high, port;
-		static u32 hint;
-		u32 offset = hint + port_offset;
+		int remaining, low, high, port;
 		struct hlist_node *node;
 		struct inet_timewait_sock *tw = NULL;
 
 		inet_get_local_port_range(&low, &high);
 		remaining = (high - low) + 1;
+		port = net_random() % remaining + low;
 
 		local_bh_disable();
-		for (i = 1; i <= remaining; i++) {
-			port = low + (i + offset) % remaining;
+		do {
 			if (inet_is_reserved_local_port(port))
-				continue;
+				goto next_nolock;
 			head = &hinfo->bhash[inet_bhashfn(net, port,
 					hinfo->bhash_size)];
 			spin_lock(&head->lock);
@@ -510,16 +508,17 @@ int __inet_hash_connect(struct inet_timewait_death_row *death_row,
 			tb->fastreuse = -1;
 			goto ok;
 
-		next_port:
+next_port:
 			spin_unlock(&head->lock);
-		}
+next_nolock:
+			if (++port > high)
+				port = low;
+		} while (--remaining > 0);
 		local_bh_enable();
 
 		return -EADDRNOTAVAIL;
 
 ok:
-		hint += i;
-
 		/* Head lock still held and bh's disabled */
 		inet_bind_hash(sk, tb, port);
 		if (sk_unhashed(sk)) {


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