From e89f5983be6a993efa26f24f31d1d0aa9ace51d4 Mon Sep 17 00:00:00 2001
From: fbernon <fbernon>
Date: Sun, 17 Jun 2007 16:15:34 +0000
Subject: [PATCH] tcp_in.c: Fix bug #20126 : Zero ssthresh bug (by Per-Henrik
 Lundblom and Kieran Mansley).

---
 src/core/tcp_in.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/src/core/tcp_in.c b/src/core/tcp_in.c
index e385525c..110d1484 100644
--- a/src/core/tcp_in.c
+++ b/src/core/tcp_in.c
@@ -701,12 +701,18 @@ tcp_receive(struct tcp_pcb *pcb)
             /*pcb->ssthresh = LWIP_MAX((pcb->snd_max -
                                       pcb->lastack) / 2,
                                       2 * pcb->mss);*/
-            /* Set ssthresh to half of the minimum of the currenct cwnd and the advertised window */
+            /* Set ssthresh to half of the minimum of the current cwnd and the advertised window */
             if (pcb->cwnd > pcb->snd_wnd)
               pcb->ssthresh = pcb->snd_wnd / 2;
             else
               pcb->ssthresh = pcb->cwnd / 2;
 
+            /* The minimum value for ssthresh should be 2 MSS */
+            if (pcb->ssthresh < 2*pcb->mss) {
+              LWIP_DEBUGF(TCP_FR_DEBUG, ("tcp_receive: The minimum value for ssthresh %"U16_F" should be min 2 mss %"U16_F"...\n", pcb->ssthresh, 2*pcb->mss));
+              pcb->ssthresh = 2*pcb->mss;
+            }
+
             pcb->cwnd = pcb->ssthresh + 3 * pcb->mss;
             pcb->flags |= TF_INFR;
           } else {