[PATCH v2 net] udpv6: reset daddr and dport in sk if connect() fails

[PATCH v2 net] udpv6: reset daddr and dport in sk if connect() fails

[Wei Wang]

From: Wei Wang <weiwan@google.com>

In __ip6_datagram_connect(), reset sk->sk_v6_daddr and inet->dport if
error occurs so that udp_v6_early_demux() won't consider this socket
as a valid candidate for early demux.

v2: fix compilation error

Signed-off-by: Wei Wang <weiwan@google.com>
Acked-by: Maciej Żenczykowski <maze@google.com>
---
 net/ipv6/datagram.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/net/ipv6/datagram.c b/net/ipv6/datagram.c
index e011122ebd43..5c786f5ab961 100644
--- a/net/ipv6/datagram.c
+++ b/net/ipv6/datagram.c
@@ -250,8 +250,14 @@ int __ip6_datagram_connect(struct sock *sk, struct sockaddr *uaddr,
 	 */
 
 	err = ip6_datagram_dst_update(sk, true);
-	if (err)
+	if (err) {
+		/* Reset daddr and dport so that udp_v6_early_demux()
+		 * fails to find this socket
+		 */
+		memset(&sk->sk_v6_daddr, 0, sizeof(sk->sk_v6_daddr));
+		inet->inet_dport = 0;
 		goto out;
+	}
 
 	sk->sk_state = TCP_ESTABLISHED;
 	sk_set_txhash(sk);
-- 
2.13.1.611.g7e3b11ae1-goog

Re: [PATCH v2 net] udpv6: reset daddr and dport in sk if connect() fails

[Maciej Żenczykowski]

So this is clearly an improvement over the current state of things.

However, I think there is still a very slight race condition in the
error case, since I imagine udp early demux might find the socket
while ip6_datagram_dst_update() is running.

It's possible that inet_dport assignment could simply be postponed
until after the ip6_datagram_dst_update() call.

Another possibility would be to make the early demux code only capable
of finding TCP_ESTABLISHED sockets.

That said, I'm not sure what the right call would be.

Re: [PATCH v2 net] udpv6: reset daddr and dport in sk if connect() fails

[David Miller]

From: Wei Wang <tracywwnj@gmail.com>
Date: Thu, 22 Jun 2017 12:03:41 -0700

> From: Wei Wang <weiwan@google.com>
> 
> In __ip6_datagram_connect(), reset sk->sk_v6_daddr and inet->dport if
> error occurs so that udp_v6_early_demux() won't consider this socket
> as a valid candidate for early demux.
> 
> v2: fix compilation error
> 
> Signed-off-by: Wei Wang <weiwan@google.com>
> Acked-by: Maciej Żenczykowski <maze@google.com>

Please also add a state test against TCP_ESTABLISHED in UDP v6 early
demux to close this race completely.

Thanks.