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-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?= <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 --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