From 68ccb8021a838066f0951d4b2817eb6b6f10a843 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] 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(-) diff -up ./slirp4netns-2244b9b6461afeccad1678fac3d6e478c28b4ad6/vendor/libslirp/src/tcp_subr.c.CVE-2020-8608 ./slirp4netns-2244b9b6461afeccad1678fac3d6e478c28b4ad6/vendor/libslirp/src/tcp_subr.c --- slirp4netns-2244b9b6461afeccad1678fac3d6e478c28b4ad6/vendor/libslirp/src/tcp_subr.c.CVE-2020-8608 2020-02-06 13:31:33.592822770 +0100 +++ slirp4netns-2244b9b6461afeccad1678fac3d6e478c28b4ad6/vendor/libslirp/src/tcp_subr.c 2020-02-06 13:31:33.594822795 +0100 @@ -640,8 +640,7 @@ int tcp_emu(struct socket *so, struct mb 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'; } @@ -681,9 +680,9 @@ int tcp_emu(struct socket *so, struct mb 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) { /* @@ -716,10 +715,9 @@ int tcp_emu(struct socket *so, struct mb 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; } @@ -742,8 +740,8 @@ int tcp_emu(struct socket *so, struct mb 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: @@ -762,10 +760,10 @@ int tcp_emu(struct socket *so, struct mb 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), @@ -773,10 +771,10 @@ int tcp_emu(struct socket *so, struct mb 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), @@ -784,10 +782,10 @@ int tcp_emu(struct socket *so, struct mb 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; From 30648c03b27fb8d9611b723184216cd3174b6775 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Marc-Andr=C3=A9=20Lureau?= Date: Mon, 27 Jan 2020 10:24:09 +0100 Subject: [PATCH] util: add slirp_fmt() helpers MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Various calls to snprintf() in libslirp 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." Introduce slirp_fmt() that handles several pathological cases the way libslirp usually expect: - treat error as fatal (instead of silently returning -1) - fmt0() will always \0 end - return the number of bytes actually written (instead of what would have been written, which would usually result in OOB later), including the ending \0 for fmt0() - warn if truncation happened (instead of ignoring) Other less common cases can still be handled with strcpy/snprintf() etc. Signed-off-by: Marc-André Lureau Reviewed-by: Samuel Thibault Message-Id: <20200127092414.169796-2-marcandre.lureau@redhat.com> --- src/util.c | 62 ++++++++++++++++++++++++++++++++++++++++++++++++++++++ src/util.h | 3 +++ 2 files changed, 65 insertions(+) diff --git a/src/util.c b/src/util.c index e596087..e3b6257 100644 --- a/vendor/libslirp/src/util.c +++ b/vendor/libslirp/src/util.c @@ -364,3 +364,65 @@ void slirp_pstrcpy(char *buf, int buf_size, const char *str) } *q = '\0'; } + +static int slirp_vsnprintf(char *str, size_t size, + const char *format, va_list args) +{ + int rv = vsnprintf(str, size, format, args); + + if (rv < 0) { + g_error("vsnprintf() failed: %s", g_strerror(errno)); + } + + return rv; +} + +/* + * A snprintf()-like function that: + * - returns the number of bytes written (excluding optional \0-ending) + * - dies on error + * - warn on truncation + */ +int slirp_fmt(char *str, size_t size, const char *format, ...) +{ + va_list args; + int rv; + + va_start(args, format); + rv = slirp_vsnprintf(str, size, format, args); + va_end(args); + + if (rv > size) { + g_critical("vsnprintf() truncation"); + } + + return MIN(rv, size); +} + +/* + * A snprintf()-like function that: + * - always \0-end (unless size == 0) + * - returns the number of bytes actually written, including \0 ending + * - dies on error + * - warn on truncation + */ +int slirp_fmt0(char *str, size_t size, const char *format, ...) +{ + va_list args; + int rv; + + va_start(args, format); + rv = slirp_vsnprintf(str, size, format, args); + va_end(args); + + if (rv >= size) { + g_critical("vsnprintf() truncation"); + if (size > 0) + str[size - 1] = '\0'; + rv = size; + } else { + rv += 1; /* include \0 */ + } + + return rv; +} diff --git a/src/util.h b/src/util.h index e9c3073..5530c46 100644 --- a/vendor/libslirp/src/util.h +++ b/vendor/libslirp/src/util.h @@ -181,4 +181,7 @@ static inline int slirp_socket_set_fast_reuse(int fd) void slirp_pstrcpy(char *buf, int buf_size, const char *str); +int slirp_fmt(char *str, size_t size, const char *format, ...); +int slirp_fmt0(char *str, size_t size, const char *format, ...); + #endif -- 2.24.1