Fix CVE-2017-13711:

https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2017-13711

Patch copied from upstream source repository:

https://git.qemu.org/?p=qemu.git;a=commitdiff;h=1201d308519f1e915866d7583d5136d03cc1d384

From 1201d308519f1e915866d7583d5136d03cc1d384 Mon Sep 17 00:00:00 2001
From: Samuel Thibault <samuel.thibault@ens-lyon.org>
Date: Fri, 25 Aug 2017 01:35:53 +0200
Subject: [PATCH] slirp: fix clearing ifq_so from pending packets
MIME-Version: 1.0
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The if_fastq and if_batchq contain not only packets, but queues of packets
for the same socket. When sofree frees a socket, it thus has to clear ifq_so
from all the packets from the queues, not only the first.

Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Cc: qemu-stable@nongnu.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
 slirp/socket.c | 39 +++++++++++++++++++++++----------------
 1 file changed, 23 insertions(+), 16 deletions(-)

diff --git a/slirp/socket.c b/slirp/socket.c
index ecec0295a9..cb7b5b608d 100644
--- a/slirp/socket.c
+++ b/slirp/socket.c
@@ -59,6 +59,27 @@ socreate(Slirp *slirp)
   return(so);
 }
 
+/*
+ * Remove references to so from the given message queue.
+ */
+static void
+soqfree(struct socket *so, struct quehead *qh)
+{
+    struct mbuf *ifq;
+
+    for (ifq = (struct mbuf *) qh->qh_link;
+             (struct quehead *) ifq != qh;
+             ifq = ifq->ifq_next) {
+        if (ifq->ifq_so == so) {
+            struct mbuf *ifm;
+            ifq->ifq_so = NULL;
+            for (ifm = ifq->ifs_next; ifm != ifq; ifm = ifm->ifs_next) {
+                ifm->ifq_so = NULL;
+            }
+        }
+    }
+}
+
 /*
  * remque and free a socket, clobber cache
  */
@@ -66,23 +87,9 @@ void
 sofree(struct socket *so)
 {
   Slirp *slirp = so->slirp;
-  struct mbuf *ifm;
 
-  for (ifm = (struct mbuf *) slirp->if_fastq.qh_link;
-       (struct quehead *) ifm != &slirp->if_fastq;
-       ifm = ifm->ifq_next) {
-    if (ifm->ifq_so == so) {
-      ifm->ifq_so = NULL;
-    }
-  }
-
-  for (ifm = (struct mbuf *) slirp->if_batchq.qh_link;
-       (struct quehead *) ifm != &slirp->if_batchq;
-       ifm = ifm->ifq_next) {
-    if (ifm->ifq_so == so) {
-      ifm->ifq_so = NULL;
-    }
-  }
+  soqfree(so, &slirp->if_fastq);
+  soqfree(so, &slirp->if_batchq);
 
   if (so->so_emu==EMU_RSH && so->extra) {
 	sofree(so->extra);
-- 
2.14.1

