https://gitlab.freedesktop.org/slirp/libslirp/-/commit/c7ede54cbd2e2b25385325600958ba0124e31cc0
https://bugzilla.redhat.com/show_bug.cgi?id=1835986
https://bugs.gentoo.org/731992

From c7ede54cbd2e2b25385325600958ba0124e31cc0 Mon Sep 17 00:00:00 2001
From: Ralf Haferkamp <rhafer@suse.com>
Date: Fri, 3 Jul 2020 14:51:16 +0200
Subject: [PATCH] Drop bogus IPv6 messages

Drop IPv6 message shorter than what's mentioned in the payload
length header (+ the size of the IPv6 header). They're invalid an could
lead to data leakage in icmp6_send_echoreply().
---
 src/ip6_input.c | 7 +++++++
 1 file changed, 7 insertions(+)

--- a/slirp/src/ip6_input.c
+++ b/slirp/src/ip6_input.c
@@ -49,6 +49,13 @@ void ip6_input(struct mbuf *m)
         goto bad;
     }
 
+    // Check if the message size is big enough to hold what's
+    // set in the payload length header. If not this is an invalid
+    // packet
+    if (m->m_len < ntohs(ip6->ip_pl) + sizeof(struct ip6)) {
+        goto bad;
+    }
+
     /* check ip_ttl for a correct ICMP reply */
     if (ip6->ip_hl == 0) {
         icmp6_send_error(m, ICMP6_TIMXCEED, ICMP6_TIMXCEED_INTRANS);
-- 
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