inet_hash_connect: source port allocation

Hello,

Please forgive me if this is a stupid question, but is there any particular reason why the source port allocation in __inet_hash_connect() shouldn't use the same random allocation that inet_csk_get_port() uses? The latter, of course, is used when bind() doesn't specify a source port but the implicit "bind" for a connect() gets its port allocated by __inet_hash_connect().

jch

Quoted 9 lines · John Haxby

Hello,

Please forgive me if this is a stupid question, but is there any particular reason why the source port allocation in __inet_hash_connect() shouldn't use the same random allocation that inet_csk_get_port() uses? The latter, of course, is used when bind() doesn't specify a source port but the implicit "bind" for a connect() gets its port allocated by __inet_hash_connect().

Quoted 1 line

jch

autobind vs bind

bind() gives more information, like local address (if any)

autobind(), we dont know local address, it'll be chose later by routing.

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?

Quoted 9 lines · John Haxby

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.

Quoted 2 lines

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.

Quoted 14 lines · Eric Dumazet

Quoted 11 lines · John Haxby

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?

Quoted 6 lines

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 :

Quoted 11 lines · Eric Dumazet

Quoted 9 lines · John Haxby

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.

Quoted 9 lines

Quoted 2 lines

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 :

net/ipv4/inet_hashtables.c +9 -8

index 1b344f3..65c3702 100644
@@ -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);