From 66e2f47a01ffcaafe11acae0a191efd1805f86c6 Mon Sep 17 00:00:00 2001
From: Prasad J Pandit <pjp@fedoraproject.org>
Date: Wed, 11 Mar 2020 18:27:22 +0800
Subject: [PATCH] slirp: use correct size while emulating commands

While emulating services in tcp_emu(), it uses 'mbuf' size
'm->m_size' to write commands via snprintf(3). Use M_FREEROOM(m)
size to avoid possible OOB access.
Signed-off-by: default avatarPrasad J Pandit <pjp@fedoraproject.org>
Signed-off-by: Samuel Thibault's avatarSamuel Thibault <samuel.thibault@ens-lyon.org>
Message-Id: <20200109094228.79764-3-ppandit@redhat.com>
---
 slirp/src/tcp_subr.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/slirp/src/tcp_subr.c b/slirp/src/tcp_subr.c
index 2053b11b..e898fd03 100644
--- a/slirp/src/tcp_subr.c
+++ b/slirp/src/tcp_subr.c
@@ -707,7 +707,7 @@ tcp_emu(struct socket *so, struct mbuf *m)
 			n4 =  (laddr & 0xff);
 
 			m->m_len = bptr - m->m_data; /* Adjust length */
-                        m->m_len += snprintf(bptr, m->m_size - m->m_len,
+                        m->m_len += snprintf(bptr, M_FREEROOM(m),
                                              "ORT %d,%d,%d,%d,%d,%d\r\n%s",
                                              n1, n2, n3, n4, n5, n6, x==7?buff:"");
 			return 1;
@@ -740,7 +740,7 @@ tcp_emu(struct socket *so, struct mbuf *m)
 			n4 =  (laddr & 0xff);
 
 			m->m_len = bptr - m->m_data; /* Adjust length */
-			m->m_len += snprintf(bptr, m->m_size - m->m_len,
+			m->m_len += snprintf(bptr, M_FREEROOM(m),
                                              "27 Entering Passive Mode (%d,%d,%d,%d,%d,%d)\r\n%s",
                                              n1, n2, n3, n4, n5, n6, x==7?buff:"");
 
@@ -766,8 +766,8 @@ tcp_emu(struct socket *so, struct mbuf *m)
 		if (m->m_data[m->m_len-1] == '\0' && lport != 0 &&
 		    (so = tcp_listen(slirp, INADDR_ANY, 0, so->so_laddr.s_addr,
 		                     htons(lport), SS_FACCEPTONCE)) != NULL)
-                    m->m_len = snprintf(m->m_data, m->m_size, "%d",
-                                        ntohs(so->so_fport)) + 1;
+                    m->m_len = snprintf(m->m_data, M_ROOM(m),
+					"%d", ntohs(so->so_fport)) + 1;
 		return 1;
 
 	 case EMU_IRC:
-- 
2.21.1 (Apple Git-122.3)