Fixes CVE-2019-6778:

https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2019-6778

Patch copied from upstream source repository:

https://git.qemu.org/?p=qemu.git;a=commitdiff;h=a7104eda7dab99d0cdbd3595c211864cba415905

From a7104eda7dab99d0cdbd3595c211864cba415905 Mon Sep 17 00:00:00 2001
From: Prasad J Pandit <pjp@fedoraproject.org>
Date: Sun, 13 Jan 2019 23:29:48 +0530
Subject: [PATCH] slirp: check data length while emulating ident function

While emulating identification protocol, tcp_emu() does not check
available space in the 'sc_rcv->sb_data' buffer. It could lead to
heap buffer overflow issue. Add check to avoid it.

Reported-by: Kira <864786842@qq.com>
Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
---
 slirp/tcp_subr.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/slirp/tcp_subr.c b/slirp/tcp_subr.c
index 4a9a5b5edc..23a841f26e 100644
--- a/slirp/tcp_subr.c
+++ b/slirp/tcp_subr.c
@@ -634,6 +634,11 @@ tcp_emu(struct socket *so, struct mbuf *m)
 			socklen_t addrlen = sizeof(struct sockaddr_in);
 			struct sbuf *so_rcv = &so->so_rcv;
 
+			if (m->m_len > so_rcv->sb_datalen
+					- (so_rcv->sb_wptr - so_rcv->sb_data)) {
+			    return 1;
+			}
+
 			memcpy(so_rcv->sb_wptr, m->m_data, m->m_len);
 			so_rcv->sb_wptr += m->m_len;
 			so_rcv->sb_rptr += m->m_len;
-- 
2.20.1

