From 68ccb8021a838066f0951d4b2817eb6b6f10a843 Mon Sep 17 00:00:00 2001

From: =?UTF-8?q?Marc-Andr=C3=A9=20Lureau?= <marcandre.lureau@redhat.com>

Date: Mon, 27 Jan 2020 10:24:14 +0100

Subject: [PATCH] tcp_emu: fix unsafe snprintf() usages

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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 <lersek@redhat.com>

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>

Reviewed-by: Samuel Thibault <samuel.thibault@ens-lyon.org>

Message-Id: <20200127092414.169796-7-marcandre.lureau@redhat.com>

---

 src/tcp_subr.c | 44 +++++++++++++++++++++-----------------------

 1 file changed, 21 insertions(+), 23 deletions(-)

diff -up slirp4netns-4992082b2af77c09bca6bd8504e2ebfa5e118c18/qemu/slirp/src/tcp_subr.c.orig slirp4netns-4992082b2af77c09bca6bd8504e2ebfa5e118c18/qemu/slirp/src/tcp_subr.c

--- slirp4netns-4992082b2af77c09bca6bd8504e2ebfa5e118c18/qemu/slirp/src/tcp_subr.c.orig	2020-02-06 14:57:07.786013242 +0100

+++ slirp4netns-4992082b2af77c09bca6bd8504e2ebfa5e118c18/qemu/slirp/src/tcp_subr.c	2020-02-06 15:14:44.678746260 +0100

@@ -709,9 +709,9 @@ 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) {

 			/*

@@ -742,10 +742,9 @@ 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;

 		}

@@ -768,9 +767,8 @@ 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));

 		return 1;

 	 case EMU_IRC:

@@ -789,10 +787,10 @@ 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),

@@ -800,10 +798,10 @@ 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),

@@ -811,10 +809,10 @@ 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;

From 30648c03b27fb8d9611b723184216cd3174b6775 Mon Sep 17 00:00:00 2001

From: =?UTF-8?q?Marc-Andr=C3=A9=20Lureau?= <marcandre.lureau@redhat.com>

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 <marcandre.lureau@redhat.com>

Reviewed-by: Samuel Thibault <samuel.thibault@ens-lyon.org>

Message-Id: <20200127092414.169796-2-marcandre.lureau@redhat.com>

---

 src/util.c | 62 ++++++++++++++++++++++++++++++++++++++++++++++++++++++

 src/util.h |  3 +++

 2 files changed, 65 insertions(+)

diff -up slirp4netns-4992082b2af77c09bca6bd8504e2ebfa5e118c18/qemu/slirp/src/util.c.orig slirp4netns-4992082b2af77c09bca6bd8504e2ebfa5e118c18/qemu/slirp/src/util.c

--- slirp4netns-4992082b2af77c09bca6bd8504e2ebfa5e118c18/qemu/slirp/src/util.c.orig	2019-03-28 12:45:09.000000000 +0100

+++ slirp4netns-4992082b2af77c09bca6bd8504e2ebfa5e118c18/qemu/slirp/src/util.c	2020-02-06 14:57:07.786013242 +0100

@@ -366,3 +366,65 @@ void slirp_pstrcpy(char *buf, int buf_si

     }

     *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 -up slirp4netns-4992082b2af77c09bca6bd8504e2ebfa5e118c18/qemu/slirp/src/util.h.orig slirp4netns-4992082b2af77c09bca6bd8504e2ebfa5e118c18/qemu/slirp/src/util.h

--- slirp4netns-4992082b2af77c09bca6bd8504e2ebfa5e118c18/qemu/slirp/src/util.h.orig	2019-03-28 12:45:09.000000000 +0100

+++ slirp4netns-4992082b2af77c09bca6bd8504e2ebfa5e118c18/qemu/slirp/src/util.h	2020-02-06 14:57:07.786013242 +0100

@@ -172,4 +172,7 @@ static inline int slirp_socket_set_fast_

 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