From 1db8bcc0ec91bb4374b3ffdd03da3c4ede381fb5 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Marc-Andr=C3=A9=20Lureau?= Date: Wed, 11 Mar 2020 18:52:07 +0800 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: default avatarLaszlo Ersek Signed-off-by: default avatarMarc-André Lureau Reviewed-by: Samuel Thibault's avatarSamuel Thibault Message-Id: <20200127092414.169796-7-marcandre.lureau@redhat.com> --- slirp/src/tcp_subr.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) diff --git a/slirp/src/tcp_subr.c b/slirp/src/tcp_subr.c index e898fd03..88dadc76 100644 --- a/slirp/src/tcp_subr.c +++ b/slirp/src/tcp_subr.c @@ -707,7 +707,7 @@ 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), + 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; @@ -740,7 +740,7 @@ 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), + 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:""); @@ -766,7 +766,7 @@ 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), + m->m_len = slirp_fmt0(m->m_data, M_ROOM(m), "%d", ntohs(so->so_fport)) + 1; return 1; @@ -786,7 +786,7 @@ 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), + 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); @@ -797,7 +797,7 @@ 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), + 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); @@ -808,7 +808,7 @@ 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), + 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); -- 2.21.1 (Apple Git-122.3)