[Slirp] [PATCH] slirp: use correct size while emulating IRC commands

[P J P]

From: Prasad J Pandit <pjp at fedoraproject.org>

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 correct
M_ROOM(m) size to avoid OOB access.

Reported-by: Vishnu Dev TJ <vishnudevtj at gmail.com>
Signed-off-by: Prasad J Pandit <pjp at fedoraproject.org>
---
 src/tcp_subr.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/src/tcp_subr.c b/src/tcp_subr.c
index 382aa38..b3af5b5 100644
--- a/src/tcp_subr.c
+++ b/src/tcp_subr.c
@@ -763,7 +763,8 @@ 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_ROOM(m) - m->m_len,
+                                 "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,
@@ -773,8 +774,8 @@ 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 SEND %s %lu %u %u%c\n", buff,
+            m->m_len += snprintf(bptr, M_ROOM(m) - m->m_len,
+                                 "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,
@@ -784,8 +785,8 @@ 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 MOVE %s %lu %u %u%c\n", buff,
+            m->m_len += snprintf(bptr, M_ROOM(m) - m->m_len,
+                                 "DCC MOVE %s %lu %u %u%c\n", buff,
                          (unsigned long)ntohl(so->so_faddr.s_addr),
                          ntohs(so->so_fport), n1, 1);
         }
-- 
2.24.1