Re: [PATCH v2 net-next] rds-tcp: Add sysctl tunables for sndbuf/rcvbuf on rds-tcp socket

On Tue, 2016-03-15 at 12:58 -0400, Sowmini Varadhan wrote:

On (03/15/16 09:38), santosh shilimkar wrote:

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+	if (rtn->sndbuf_size > 0) {

So value of 1 is allowed as well. There should be some
minimum default or multiple of it. Of course above check
can remain as is as long as you validate the user input
in handlers.

yes, just as user-space SO_SNDBUF allows ridiculous values
for buffer size..

Well... Not really.

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@@ -309,6 +352,7 @@ static void __net_exit rds_tcp_exit_net(struct net *net)
 {
 	struct rds_tcp_net *rtn = net_generic(net, rds_tcp_netid);

+	unregister_net_sysctl_table(rtn->rds_tcp_sysctl);
 	/* If rds_tcp_exit_net() is called as a result of netns deletion,
 	 * the rds_tcp_kill_sock() device notifier would already have cleaned
 	 * up the listen socket, thus there is no work to do in this function.

You need to unregister it on rds_tcp_listen_init() failure.

Ok, good point.

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+	rtn->sndbuf_size = user_atoi(buffer, *lenp);

As mentioned above, you should make sure the buffer lengths are
legitimate.

As above. We allow any values that the TCP socket itself allows.
If the user wants to shoot themself in the foot, we dont stop them.

Look at SO_SNDBUF and SO_RCVBUF implementation.

sk->sk_sndbuf = max_t(u32, val * 2, SOCK_MIN_SNDBUF);

sk->sk_rcvbuf = max_t(u32, val * 2, SOCK_MIN_RCVBUF);

kernel definitely has some logic here.

If you believe SOCK_MIN_SNDBUF and/or SOCK_MIN_RCVBUF are wrong, please
elaborate.