Commit 68ccb802 authored by Marc-André Lureau's avatar Marc-André Lureau

tcp_emu: fix unsafe snprintf() usages

Various calls to snprintf() assume that snprintf() returns "only" the
number of bytes written (excluding terminating NUL).

https://pubs.opengroup.org/onlinepubs/9699919799/functions/snprintf.html#tag_16_159_04

"Upon successful completion, the snprintf() function shall return the
number of bytes that would be written to s had n been sufficiently
large excluding the terminating null byte."

Before patch ce131029, if there isn't enough room in "m_data" for the
"DCC ..." message, we overflow "m_data".

After the patch, if there isn't enough room for the same, we don't
overflow "m_data", but we set "m_len" out-of-bounds. The next time an
access is bounded by "m_len", we'll have a buffer overflow then.

Use slirp_fmt*() to fix potential OOB memory access.
Reported-by: default avatarLaszlo Ersek <lersek@redhat.com>
Signed-off-by: default avatarMarc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Samuel Thibault's avatarSamuel Thibault <samuel.thibault@ens-lyon.org>
Message-Id: <20200127092414.169796-7-marcandre.lureau@redhat.com>
parent c8ee10e2
Pipeline #101689 passed with stage
in 1 minute and 20 seconds
......@@ -643,8 +643,7 @@ int tcp_emu(struct socket *so, struct mbuf *m)
NTOHS(n1);
NTOHS(n2);
m_inc(m, snprintf(NULL, 0, "%d,%d\r\n", n1, n2) + 1);
m->m_len = snprintf(m->m_data, M_ROOM(m), "%d,%d\r\n", n1, n2);
assert(m->m_len < M_ROOM(m));
m->m_len = slirp_fmt(m->m_data, M_ROOM(m), "%d,%d\r\n", n1, n2);
} else {
*eol = '\r';
}
......@@ -684,9 +683,9 @@ 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_FREEROOM(m),
"ORT %d,%d,%d,%d,%d,%d\r\n%s", n1, n2, n3, n4,
n5, n6, x == 7 ? buff : "");
m->m_len += slirp_fmt(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;
} else if ((bptr = (char *)strstr(m->m_data, "27 Entering")) != NULL) {
/*
......@@ -719,10 +718,9 @@ 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_FREEROOM(m),
"27 Entering Passive Mode (%d,%d,%d,%d,%d,%d)\r\n%s",
n1, n2, n3, n4, n5, n6, x == 7 ? buff : "");
m->m_len += slirp_fmt(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 : "");
return 1;
}
......@@ -745,8 +743,8 @@ int 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_ROOM(m),
"%d", ntohs(so->so_fport)) + 1;
m->m_len = slirp_fmt0(m->m_data, M_ROOM(m),
"%d", ntohs(so->so_fport));
return 1;
case EMU_IRC:
......@@ -765,10 +763,10 @@ 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_FREEROOM(m),
"DCC CHAT chat %lu %u%c\n",
(unsigned long)ntohl(so->so_faddr.s_addr),
ntohs(so->so_fport), 1);
m->m_len += slirp_fmt(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,
&n1) == 4) {
if ((so = tcp_listen(slirp, INADDR_ANY, 0, htonl(laddr),
......@@ -776,10 +774,10 @@ 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_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);
m->m_len += slirp_fmt(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,
&n1) == 4) {
if ((so = tcp_listen(slirp, INADDR_ANY, 0, htonl(laddr),
......@@ -787,10 +785,10 @@ 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_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);
m->m_len += slirp_fmt(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);
}
return 1;
......
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