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From 90b1929638fb5fed4e5fc65f95b7a76e339e0640 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Philippe=20Mathieu-Daud=C3=A9?= <philmd@redhat.com>
Date: Mon, 9 Sep 2019 09:13:33 +0200
Subject: [PATCH 01/12] 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: <20190909091333.18511-2-philmd@redhat.com>
Patchwork-id: 90336
O-Subject: [RHEL-7.8 qemu-kvm PATCH 1/1] Using ip_deq after m_free might read pointers from an allocation reuse.
Bugzilla: 1749735
RH-Acked-by: John Snow <jsnow@redhat.com>
RH-Acked-by: Stefano Garzarella <sgarzare@redhat.com>
RH-Acked-by: Thomas Huth <thuth@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: Miroslav Rezanina <mrezanin@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 5226224..9e95b40 100644
--- a/slirp/ip_input.c
+++ b/slirp/ip_input.c
@@ -296,6 +296,7 @@ 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;
@@ -303,9 +304,10 @@ 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