From a6a92d42f99de4fc19f74606a920bd33b7235fc0 Mon Sep 17 00:00:00 2001
From: sg <goldsimon@gmx.de>
Date: Thu, 26 Feb 2015 21:23:40 +0100
Subject: [PATCH] Fixed bug #41700 (Call to tcp_listen_dual() should not accept
 IPv4 listen PCB args)

---
 src/core/tcp.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/src/core/tcp.c b/src/core/tcp.c
index 2bcf2dc4..3cbde688 100644
--- a/src/core/tcp.c
+++ b/src/core/tcp.c
@@ -591,6 +591,21 @@ struct tcp_pcb *
 tcp_listen_dual_with_backlog(struct tcp_pcb *pcb, u8_t backlog)
 {
   struct tcp_pcb *lpcb;
+  struct tcp_pcb_listen *l;
+
+  /* Dual listen only works on bound pcbs (or else we cannot check for
+      duplicate port use. */
+  if (pcb->local_port == 0) {
+    return NULL;
+  }
+  /* Check that there's noone listening on this port already
+     (don't check the IP address since we'll set it to ANY */
+  for(l = tcp_listen_pcbs.listen_pcbs; l != NULL; l = l->next) {
+    if (l->local_port == pcb->local_port) {
+      /* this port is already used */
+      return NULL;
+    }
+  }
 
   lpcb = tcp_listen_with_backlog(pcb, backlog);
   if ((lpcb != NULL) &&