File CVE-2019-15890-qemuu-slirp-use-after-free-during-packet-reassembly.patch of Package xen.14030

References: bsc#1149813 CVE-2019-15890

Subject: ip_reass: Fix use after free
From: Samuel Thibault samuel.thibault@ens-lyon.org Mon Aug 26 00:55:03 2019 +0200
Date: Mon Aug 26 00:55:03 2019 +0200:
Git: c59279437eda91841b9d26079c70b8a540d41204

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>

Index: xen-4.5.5-testing/tools/qemu-xen-dir-remote/slirp/ip_input.c
===================================================================
--- xen-4.5.5-testing.orig/tools/qemu-xen-dir-remote/slirp/ip_input.c
+++ xen-4.5.5-testing/tools/qemu-xen-dir-remote/slirp/ip_input.c
@@ -296,6 +296,7 @@ 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;
@@ -303,9 +304,10 @@ 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: