From 662aa4f1d168b32335a4dc40782e816329afcac0 Mon Sep 17 00:00:00 2001
From: Prasad J Pandit <pjp@fedoraproject.org>
Date: Tue, 14 Apr 2020 18:36:12 +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 | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/slirp/src/tcp_subr.c b/slirp/src/tcp_subr.c
index 2a15b16a..019b637a 100644
--- a/slirp/src/tcp_subr.c
+++ b/slirp/src/tcp_subr.c
@@ -696,7 +696,7 @@ int 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;
@@ -732,7 +732,7 @@ int tcp_emu(struct socket *so, struct mbuf *m)

             m->m_len = bptr - m->m_data; /* Adjust length */
             m->m_len +=
-                snprintf(bptr, m->m_size - 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 : "");

@@ -759,7 +759,8 @@ int tcp_emu(struct socket *so, struct mbuf *m)
             (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;
+                snprintf(m->m_data, M_ROOM(m),
+                            "%d", ntohs(so->so_fport)) + 1;
         return 1;

     case EMU_IRC:
--
2.23.0
