From c59279437eda91841b9d26079c70b8a540d41204 Mon Sep 17 00:00:00 2001 From: Samuel Thibault Date: Mon, 26 Aug 2019 00:55:03 +0200 Subject: [PATCH] ip_reass: Fix use after free 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 --- src/ip_input.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff -up slirp4netns-4992082b2af77c09bca6bd8504e2ebfa5e118c18/qemu/slirp/src/ip_input.c.CVE-2019-15890 slirp4netns-4992082b2af77c09bca6bd8504e2ebfa5e118c18/qemu/slirp/src/ip_input.c --- slirp4netns-4992082b2af77c09bca6bd8504e2ebfa5e118c18/qemu/slirp/src/ip_input.c.CVE-2019-15890 2020-02-26 14:58:52.081548244 +0100 +++ slirp4netns-4992082b2af77c09bca6bd8504e2ebfa5e118c18/qemu/slirp/src/ip_input.c 2020-02-26 15:00:48.144123448 +0100 @@ -297,6 +297,7 @@ 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; @@ -304,9 +305,10 @@ 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: