From 0f659af4870f151e25a7d2184b9a383bff58e3ba Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Marc-Andr=C3=A9=20Lureau?= <marcandre.lureau@redhat.com>
Date: Fri, 17 Jan 2020 12:07:57 +0100
Subject: [PATCH 2/4] slirp: use correct size while emulating IRC commands
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RH-Author: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-id: <20200117120758.1076549-3-marcandre.lureau@redhat.com>
Patchwork-id: 93400
O-Subject: [RHEL-AV-8.1.0 qemu-kvm + RHEL-AV-8.2.0 qemu-kvm PATCH 2/3] slirp: use correct size while emulating IRC commands
Bugzilla: 1791568
RH-Acked-by: Philippe Mathieu-Daudé <philmd@redhat.com>
RH-Acked-by: Stefano Garzarella <sgarzare@redhat.com>
RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>

From: Prasad J Pandit <pjp@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 M_FREEROOM(m)
size to avoid OOB access.

Reported-by: Vishnu Dev TJ <vishnudevtj@gmail.com>
Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
Reviewed-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Message-Id: <20200109094228.79764-2-ppandit@redhat.com>

(cherry picked from libslirp commit ce131029d6d4a405cb7d3ac6716d03e58fb4a5d9)
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>

Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
---
 slirp/src/tcp_subr.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/slirp/src/tcp_subr.c b/slirp/src/tcp_subr.c
index cbecd64..cedbfb2 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,
@@ -788,8 +789,8 @@ 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_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,
@@ -799,8 +800,8 @@ 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_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);
         }
-- 
1.8.3.1