tcp/dccp: fix behavior of stale SYN_RECV request sockets

When a TCP/DCCP listener is closed, its pending SYN_RECV request sockets
become stale, meaning 3WHS can not complete.

But current behavior is wrong :
incoming packets finding such stale sockets are dropped.

We need instead to cleanup the request socket and perform another
lookup :
- Incoming ACK will give a RST answer,
- SYN rtx might find another listener if available.
- We expedite cleanup of request sockets and old listener socket.

Fixes: 079096f103fa ("tcp/dccp: install syn_recv requests into ehash table")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 7 insertions, 8 deletions

diff --git a/net/dccp/ipv4.c b/net/dccp/ipv4.c
index 8e99681c8189..0dcf1963b323 100644
--- a/net/dccp/ipv4.c
+++ b/net/dccp/ipv4.c
@@ -799,15 +799,10 @@ static int dccp_v4_rcv(struct sk_buff *skb)
                                   DCCP_SKB_CB(skb)->dccpd_ack_seq);
         }
 
-        /* Step 2:
-         *      Look up flow ID in table and get corresponding socket */
+lookup:
         sk = __inet_lookup_skb(&dccp_hashinfo, skb,
                                dh->dccph_sport, dh->dccph_dport);
-        /*
-         * Step 2:
-         *      If no socket ...
-         */
-        if (sk == NULL) {
+        if (!sk) {
                 dccp_pr_debug("failed to look up flow ID in table and "
                               "get corresponding socket\n");
                 goto no_dccp_socket;
@@ -830,8 +825,12 @@ static int dccp_v4_rcv(struct sk_buff *skb)
                 struct sock *nsk = NULL;
 
                 sk = req->rsk_listener;
-                if (sk->sk_state == DCCP_LISTEN)
+                if (likely(sk->sk_state == DCCP_LISTEN)) {
                         nsk = dccp_check_req(sk, skb, req);
+                } else {
+                        inet_csk_reqsk_queue_drop(sk, req);
+                        goto lookup;
+                }
                 if (!nsk) {
                         reqsk_put(req);
                         goto discard_it;