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From a4c22009a465ebe5fd0c09699e61ad0423b8849d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Philippe=20Mathieu-Daud=C3=A9?= <philmd@redhat.com>
Date: Fri, 6 Sep 2019 14:00:34 +0100
Subject: [PATCH 07/22] 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: <20190906140034.19722-2-philmd@redhat.com>
Patchwork-id: 90306
O-Subject: [RHEL-7.7 qemu-kvm-ma + RHEL-7.7 qemu-kvm-rhev + RHEL-8.1.0 qemu-kvm PATCH 1/1] Using ip_deq after m_free might read pointers from an allocation reuse.
Bugzilla: 1749724
RH-Acked-by: Thomas Huth <thuth@redhat.com>
RH-Acked-by: Stefano Garzarella <sgarzare@redhat.com>
RH-Acked-by: Stefan Hajnoczi <stefanha@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/ip_input.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/slirp/ip_input.c b/slirp/ip_input.c
index 07d8808..7cf0133 100644
--- a/slirp/ip_input.c
+++ b/slirp/ip_input.c
@@ -300,6 +300,7 @@ 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;
@@ -307,9 +308,10 @@ 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:
-- 
1.8.3.1