From 011880f527ff317a40769ea8673a6353e5db53ac Mon Sep 17 00:00:00 2001
From: Prasad J Pandit <pjp@fedoraproject.org>
Date: Tue, 14 Apr 2020 18:23:23 +0800
Subject: [PATCH] slirp: use correct size while emulating IRC commands

While emulating IRC DCC commands, tcp_emu() uses 'mbuf' size
'm->m_size' to write DCC commands via snprintf(3). This may
lead to OOB write access, because 'bptr' points somewhere in
the middle of 'mbuf' buffer, not at the start. Use M_FREEROOM(m)
size to avoid OOB access.
Reported-by: default avatarVishnu Dev TJ <vishnudevtj@gmail.com>
Signed-off-by: default avatarPrasad J Pandit <pjp@fedoraproject.org>
Reviewed-by: Samuel Thibault's avatarSamuel Thibault <samuel.thibault@ens-lyon.org>
Message-Id: <20200109094228.79764-2-ppandit@redhat.com>
---
 slirp/src/tcp_subr.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/slirp/src/tcp_subr.c b/slirp/src/tcp_subr.c
index 9c94c03a..2a15b16a 100644
--- a/slirp/src/tcp_subr.c
+++ b/slirp/src/tcp_subr.c
@@ -778,7 +778,8 @@ int tcp_emu(struct socket *so, struct mbuf *m)
                 return 1;
             }
             m->m_len = bptr - m->m_data; /* Adjust length */
-            m->m_len += snprintf(bptr, m->m_size, "DCC CHAT chat %lu %u%c\n",
+            m->m_len += snprintf(bptr, M_FREEROOM(m),
+                                 "DCC CHAT chat %lu %u%c\n",
                                  (unsigned long)ntohl(so->so_faddr.s_addr),
                                  ntohs(so->so_fport), 1);
         } else if (sscanf(bptr, "DCC SEND %256s %u %u %u", buff, &laddr, &lport,
@@ -789,7 +790,8 @@ 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, "DCC SEND %s %lu %u %u%c\n", buff,
+                snprintf(bptr, M_FREEROOM(m),
+                         "DCC SEND %s %lu %u %u%c\n", buff,
                          (unsigned long)ntohl(so->so_faddr.s_addr),
                          ntohs(so->so_fport), n1, 1);
         } else if (sscanf(bptr, "DCC MOVE %256s %u %u %u", buff, &laddr, &lport,
@@ -800,7 +802,8 @@ 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, "DCC MOVE %s %lu %u %u%c\n", buff,
+                snprintf(bptr, M_FREEROOM(m),
+                         "DCC MOVE %s %lu %u %u%c\n", buff,
                          (unsigned long)ntohl(so->so_faddr.s_addr),
                          ntohs(so->so_fport), n1, 1);
         }
--
2.23.0