From baf30f5eaef823950e8b337d9e5e47bb4e1e4524 Mon Sep 17 00:00:00 2001
From: kieranm <kieranm>
Date: Tue, 31 Mar 2009 10:55:31 +0000
Subject: [PATCH] BUG20779: cope with SYN packets received during established
 states, and retransmission of initial SYN.

---
 CHANGELOG         |  3 +++
 src/core/tcp_in.c | 12 ++++++++++--
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/CHANGELOG b/CHANGELOG
index 5732efba..522a9791 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -76,6 +76,9 @@ HISTORY
   ++ Bugfixes:
 
   2009-03-31 Kieran Mansley
+  * tcp_in.c: cope with SYN packets received during established states,
+    and retransmission of initial SYN.
+
   * tcp_out.c: set push bit correctly when tcp segments are merged
 
   2009-03-27 Kieran Mansley
diff --git a/src/core/tcp_in.c b/src/core/tcp_in.c
index a1e52fcd..ee83dac3 100644
--- a/src/core/tcp_in.c
+++ b/src/core/tcp_in.c
@@ -536,6 +536,12 @@ tcp_process(struct tcp_pcb *pcb)
     }
   }
 
+  if ((flags & TCP_SYN) && (pcb->state != SYN_SENT && pcb->state != SYN_RCVD)) { 
+    /* Cope with new connection attempt after remote end crashed */
+    tcp_ack_now(pcb);
+    return ERR_OK;
+  }
+  
   /* Update the PCB (in)activity timer. */
   pcb->tmr = tcp_ticks;
   pcb->keep_cnt_sent = 0;
@@ -597,8 +603,7 @@ tcp_process(struct tcp_pcb *pcb)
     }
     break;
   case SYN_RCVD:
-    if (flags & TCP_ACK &&
-       !(flags & TCP_RST)) {
+    if (flags & TCP_ACK) {
       /* expected ACK number? */
       if (TCP_SEQ_BETWEEN(ackno, pcb->lastack+1, pcb->snd_nxt)) {
         u16_t old_cwnd;
@@ -633,6 +638,9 @@ tcp_process(struct tcp_pcb *pcb)
         tcp_rst(ackno, seqno + tcplen, &(iphdr->dest), &(iphdr->src),
                 tcphdr->dest, tcphdr->src);
       }
+    } else if ((flags & TCP_SYN) && (seqno == pcb->rcv_nxt - 1)) {
+      /* Looks like another copy of the SYN - retransmit our SYN-ACK */
+      tcp_rexmit(pcb);
     }
     break;
   case CLOSE_WAIT: