[PATCH net] udp6: set dst cache for a connected sk before udp_v6_send_skb

[Alexey Kodanev <alexey.kodanev@oracle.com>]

After commit 33c162a980fe ("ipv6: datagram: Update dst cache of a
connected datagram sk during pmtu update"), when the error occurs on
sending datagram in udpv6_sendmsg() due to ICMPV6_PKT_TOOBIG type,
error handler can trigger the following path and call ip6_dst_store():

    udpv6_err()
        ip6_sk_update_pmtu()
            ip6_datagram_dst_update()
                ip6_dst_lookup_flow(), can create a RTF_CACHE clone
                ...
                ip6_dst_store()

It can happen before a connected UDP socket invokes ip6_dst_store()
in the end of udpv6_sendmsg(), on destination release, as a result,
the last one changes dst to the old one, preventing getting updated
dst cache on the next udpv6_sendmsg() call.

This patch moves ip6_dst_store() in udpv6_sendmsg(), so that it is
invoked after ip6_sk_dst_lookup_flow() and before udp_v6_send_skb().

Signed-off-by: Alexey Kodanev <alexey.kodanev@oracle.com>
---
 net/ipv6/udp.c | 22 +++++++++++-----------
 1 file changed, 11 insertions(+), 11 deletions(-)

diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index 52e3ea0..0d413c6 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -1299,6 +1299,16 @@ int udpv6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 	if (ipc6.hlimit < 0)
 		ipc6.hlimit = ip6_sk_dst_hoplimit(np, &fl6, dst);
 
+	if (connected)
+		ip6_dst_store(sk, dst,
+			      ipv6_addr_equal(&fl6.daddr, &sk->sk_v6_daddr) ?
+			      &sk->sk_v6_daddr : NULL,
+#ifdef CONFIG_IPV6_SUBTREES
+			      ipv6_addr_equal(&fl6.saddr, &np->saddr) ?
+			      &np->saddr :
+#endif
+			      NULL);
+
 	if (msg->msg_flags&MSG_CONFIRM)
 		goto do_confirm;
 back_from_confirm:
@@ -1350,18 +1360,8 @@ int udpv6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 
 release_dst:
 	if (dst) {
-		if (connected) {
-			ip6_dst_store(sk, dst,
-				      ipv6_addr_equal(&fl6.daddr, &sk->sk_v6_daddr) ?
-				      &sk->sk_v6_daddr : NULL,
-#ifdef CONFIG_IPV6_SUBTREES
-				      ipv6_addr_equal(&fl6.saddr, &np->saddr) ?
-				      &np->saddr :
-#endif
-				      NULL);
-		} else {
+		if (!connected)
 			dst_release(dst);
-		}
 		dst = NULL;
 	}
 
-- 
1.8.3.1