From 4fc0d23e8f6d795c679623d2ed2cbe6a7a17b9c7 Mon Sep 17 00:00:00 2001 From: Li Zhou Date: Tue, 10 Sep 2019 20:02:15 -0700 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 Upstream-Status: Backport CVE: CVE-2019-15890 Signed-off-by: Li Zhou --- slirp/src/ip_input.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/slirp/src/ip_input.c b/slirp/src/ip_input.c index 8c75d914..c07d7d40 100644 --- a/slirp/src/ip_input.c +++ b/slirp/src/ip_input.c @@ -292,6 +292,7 @@ static struct ip *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; @@ -299,9 +300,10 @@ static struct ip *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: -- 2.23.0