Backport of: From 68ccb8021a838066f0951d4b2817eb6b6f10a843 Mon Sep 17 00:00:00 2001 From: Marc-André Lureau Date: Mon, 27 Jan 2020 10:24:14 +0100 Subject: [PATCH] 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> --- src/tcp_subr.c | 44 +++++++++++++++++++++----------------------- 1 file changed, 21 insertions(+), 23 deletions(-) --- a/slirp/tcp_subr.c +++ b/slirp/tcp_subr.c @@ -650,9 +650,9 @@ tcp_emu(struct socket *so, struct mbuf * 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) { /* @@ -683,9 +683,9 @@ tcp_emu(struct socket *so, struct mbuf * 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; } @@ -709,8 +709,8 @@ tcp_emu(struct socket *so, struct mbuf * 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)) + 1; return 1; case EMU_IRC: @@ -729,10 +729,10 @@ tcp_emu(struct socket *so, struct mbuf * 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), htons(lport), @@ -740,10 +740,10 @@ tcp_emu(struct socket *so, struct mbuf * 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), htons(lport), @@ -751,10 +751,10 @@ tcp_emu(struct socket *so, struct mbuf * 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;