From ab9ebc29bb9bb142e73a160750a451d40bfe9746 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Philippe=20Mathieu-Daud=C3=A9?= <philmd@redhat.com>
Date: Mon, 16 Sep 2019 17:07:00 +0100
Subject: Using ip_deq after m_free might read pointers from an allocation
 reuse.
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RH-Author: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-id: <20190916170700.647-2-philmd@redhat.com>
Patchwork-id: 90470
O-Subject: [RHEL-AV-8.1.0 qemu-kvm PATCH 1/1] Using ip_deq after m_free might read pointers from an allocation reuse.
Bugzilla: 1749737
RH-Acked-by: Danilo de Paula <ddepaula@redhat.com>
RH-Acked-by: John Snow <jsnow@redhat.com>

From: Samuel Thibault <samuel.thibault@ens-lyon.org>

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>
(cherry picked from libslirp commit c59279437eda91841b9d26079c70b8a540d41204)
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>

Signed-off-by: Danilo C. L. de Paula <ddepaula@redhat.com>
---
 slirp/src/ip_input.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/slirp/src/ip_input.c b/slirp/src/ip_input.c
index 8c75d91495..df1c846ade 100644
--- a/slirp/src/ip_input.c
+++ b/slirp/src/ip_input.c
@@ -292,6 +292,7 @@ static struct ip *ip_reass(Slirp *slirp, struct ip *ip, struct ipq *fp)
      */
     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;
@@ -299,9 +300,11 @@ static struct ip *ip_reass(Slirp *slirp, struct ip *ip, struct ipq *fp)
             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:
-- 
2.21.0