From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Marc-Andr=C3=A9=20Lureau?= Date: Mon, 27 Jan 2020 10:24:14 +0100 Subject: [PATCH 2/2] tcp_emu: fix unsafe snprintf() usages MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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: Laszlo Ersek Signed-off-by: Marc-André Lureau Reviewed-by: Samuel Thibault Message-Id: <20200127092414.169796-7-marcandre.lureau@redhat.com> Signed-off-by: Oguz Bektas --- slirp/src/tcp_subr.c | 44 +++++++++++++++++++++----------------------- 1 file changed, 21 insertions(+), 23 deletions(-) diff --git a/slirp/src/tcp_subr.c b/slirp/src/tcp_subr.c index d6dd133..93b3488 100644 --- a/slirp/src/tcp_subr.c +++ b/slirp/src/tcp_subr.c @@ -655,8 +655,7 @@ 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'; } @@ -696,9 +695,9 @@ 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->m_size - m->m_len, - "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) { /* @@ -731,11 +730,9 @@ 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->m_size - m->m_len, - "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; } @@ -758,8 +755,8 @@ 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->m_size, "%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: @@ -778,9 +775,10 @@ 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->m_size, "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), @@ -788,10 +786,10 @@ 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->m_size, "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), @@ -799,10 +797,10 @@ 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->m_size, "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; -- 2.20.1