From c59279437eda91841b9d26079c70b8a540d41204 Mon Sep 17 00:00:00 2001
From: Samuel Thibault <samuel.thibault@ens-lyon.org>
Date: Mon, 26 Aug 2019 00:55:03 +0200
Subject: [PATCH] ip_reass: Fix use after free

Using ip_deq after m_free might read pointers from an allocation reuse.

This would be difficult to exploit, but that is still related with
CVE-2019-14378 which generates fragmented IP packets that would trigger this
issue and at least produce a DoS.

Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
---
 src/ip_input.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff -up slirp4netns-4992082b2af77c09bca6bd8504e2ebfa5e118c18/qemu/slirp/src/ip_input.c.CVE-2019-15890 slirp4netns-4992082b2af77c09bca6bd8504e2ebfa5e118c18/qemu/slirp/src/ip_input.c
--- slirp4netns-4992082b2af77c09bca6bd8504e2ebfa5e118c18/qemu/slirp/src/ip_input.c.CVE-2019-15890	2020-02-26 14:58:52.081548244 +0100
+++ slirp4netns-4992082b2af77c09bca6bd8504e2ebfa5e118c18/qemu/slirp/src/ip_input.c	2020-02-26 15:00:48.144123448 +0100
@@ -297,6 +297,7 @@ ip_reass(Slirp *slirp, struct ip *ip, st
 	 */
 	while (q != (struct ipasfrag*)&fp->frag_link &&
             ip->ip_off + ip->ip_len > q->ipf_off) {
+		struct ipasfrag *prev;
 		i = (ip->ip_off + ip->ip_len) - q->ipf_off;
 		if (i < q->ipf_len) {
 			q->ipf_len -= i;
@@ -304,9 +305,10 @@ ip_reass(Slirp *slirp, struct ip *ip, st
 			m_adj(dtom(slirp, q), i);
 			break;
 		}
+		prev = q;
 		q = q->ipf_next;
-		m_free(dtom(slirp, q->ipf_prev));
-		ip_deq(q->ipf_prev);
+		ip_deq(prev);
+		m_free(dtom(slirp, prev));
 	}
 
 insert: