tcp: improve fastopen icmp handling

If a fast open socket is already accepted by the user, it should
be treated like a connected socket to record the ICMP error in
sk_softerr, so the user can fetch it. Do that in both tcp_v4_err
and tcp_v6_err.

Also refactor the sequence window check to improve readability
(e.g., there were two local variables named 'req').

Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Daniel Lee <longinus00@gmail.com>
Signed-off-by: Jerry Chu <hkchu@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 14 insertions, 21 deletions

diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 1665f0f84233..a2780e5334c9 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -336,8 +336,8 @@ void tcp_v4_err(struct sk_buff *icmp_skb, u32 info)
         const int code = icmp_hdr(icmp_skb)->code;
         struct sock *sk;
         struct sk_buff *skb;
-        struct request_sock *req;
-        __u32 seq;
+        struct request_sock *fastopen;
+        __u32 seq, snd_una;
         __u32 remaining;
         int err;
         struct net *net = dev_net(icmp_skb->dev);
@@ -378,12 +378,12 @@ void tcp_v4_err(struct sk_buff *icmp_skb, u32 info)
 
         icsk = inet_csk(sk);
         tp = tcp_sk(sk);
-        req = tp->fastopen_rsk;
         seq = ntohl(th->seq);
+        /* XXX (TFO) - tp->snd_una should be ISN (tcp_create_openreq_child() */
+        fastopen = tp->fastopen_rsk;
+        snd_una = fastopen ? tcp_rsk(fastopen)->snt_isn : tp->snd_una;
         if (sk->sk_state != TCP_LISTEN &&
-            !between(seq, tp->snd_una, tp->snd_nxt) &&
-            (req == NULL || seq != tcp_rsk(req)->snt_isn)) {
-                /* For a Fast Open socket, allow seq to be snt_isn. */
+            !between(seq, snd_una, tp->snd_nxt)) {
                 NET_INC_STATS_BH(net, LINUX_MIB_OUTOFWINDOWICMPS);
                 goto out;
         }
@@ -426,11 +426,9 @@ void tcp_v4_err(struct sk_buff *icmp_skb, u32 info)
                 if (code != ICMP_NET_UNREACH && code != ICMP_HOST_UNREACH)
                         break;
                 if (seq != tp->snd_una  || !icsk->icsk_retransmits ||
-                    !icsk->icsk_backoff)
+                    !icsk->icsk_backoff || fastopen)
                         break;
 
-                /* XXX (TFO) - revisit the following logic for TFO */
-
                 if (sock_owned_by_user(sk))
                         break;
 
@@ -462,14 +460,6 @@ void tcp_v4_err(struct sk_buff *icmp_skb, u32 info)
                 goto out;
         }
 
-        /* XXX (TFO) - if it's a TFO socket and has been accepted, rather
-         * than following the TCP_SYN_RECV case and closing the socket,
-         * we ignore the ICMP error and keep trying like a fully established
-         * socket. Is this the right thing to do?
-         */
-        if (req && req->sk == NULL)
-                goto out;
-
         switch (sk->sk_state) {
                 struct request_sock *req, **prev;
         case TCP_LISTEN:
@@ -502,10 +492,13 @@ void tcp_v4_err(struct sk_buff *icmp_skb, u32 info)
                 goto out;
 
         case TCP_SYN_SENT:
-        case TCP_SYN_RECV:  /* Cannot happen.
-                               It can f.e. if SYNs crossed,
-                               or Fast Open.
-                             */
+        case TCP_SYN_RECV:
+                /* Only in fast or simultaneous open. If a fast open socket is
+                 * is already accepted it is treated as a connected one below.
+                 */
+                if (fastopen && fastopen->sk == NULL)
+                        break;
+
                 if (!sock_owned_by_user(sk)) {
                         sk->sk_err = err;