CVE-2013-2168: _dbus_printf_string_upper_bound: copy the va_list for each use

Using a va_list more than once is non-portable: it happens to work
under the ABI of (for instance) x86 Linux, but not x86-64 Linux.

This led to _dbus_printf_string_upper_bound() crashing if it should
have returned exactly 1024 bytes. Many system services can be induced
to process a caller-controlled string in ways that
end up using _dbus_printf_string_upper_bound(), so this is a denial of
service.

Reviewed-by: Thiago Macieira <thiago@kde.org>

2 files changed, 20 insertions, 5 deletions

diff --git a/dbus/dbus-sysdeps-unix.c b/dbus/dbus-sysdeps-unix.c
index 0e4ccc40..626e7e62 100644
--- a/dbus/dbus-sysdeps-unix.c
+++ b/dbus/dbus-sysdeps-unix.c
@@ -3051,8 +3051,11 @@ _dbus_printf_string_upper_bound (const char *format,
   char static_buf[1024];
   int bufsize = sizeof (static_buf);
   int len;
+  va_list args_copy;
 
-  len = vsnprintf (static_buf, bufsize, format, args);
+  DBUS_VA_COPY (args_copy, args);
+  len = vsnprintf (static_buf, bufsize, format, args_copy);
+  va_end (args_copy);
 
   /* If vsnprintf() returned non-negative, then either the string fits in
    * static_buf, or this OS has the POSIX and C99 behaviour where vsnprintf
@@ -3068,8 +3071,12 @@ _dbus_printf_string_upper_bound (const char *format,
        * or the real length could be coincidentally the same. Which is it?
        * If vsnprintf returns the truncated length, we'll go to the slow
        * path. */
-      if (vsnprintf (static_buf, 1, format, args) == 1)
+      DBUS_VA_COPY (args_copy, args);
+
+      if (vsnprintf (static_buf, 1, format, args_copy) == 1)
         len = -1;
+
+      va_end (args_copy);
     }
 
   /* If vsnprintf() returned negative, we have to do more work.
@@ -3085,7 +3092,10 @@ _dbus_printf_string_upper_bound (const char *format,
       if (buf == NULL)
         return -1;
 
-      len = vsnprintf (buf, bufsize, format, args);
+      DBUS_VA_COPY (args_copy, args);
+      len = vsnprintf (buf, bufsize, format, args_copy);
+      va_end (args_copy);
+
       dbus_free (buf);
 
       /* If the reported length is exactly the buffer size, round up to the
diff --git a/dbus/dbus-sysdeps-win.c b/dbus/dbus-sysdeps-win.c
index d3ea47c2..4fff6285 100644
--- a/dbus/dbus-sysdeps-win.c
+++ b/dbus/dbus-sysdeps-win.c
@@ -538,9 +538,12 @@ int _dbus_printf_string_upper_bound (const char *format,
   char buf[1024];
   int bufsize;
   int len;
+  va_list args_copy;
 
   bufsize = sizeof (buf);
-  len = _vsnprintf (buf, bufsize - 1, format, args);
+  DBUS_VA_COPY (args_copy, args);
+  len = _vsnprintf (buf, bufsize - 1, format, args_copy);
+  va_end (args_copy);
 
   while (len == -1) /* try again */
     {
@@ -553,7 +556,9 @@ int _dbus_printf_string_upper_bound (const char *format,
       if (p == NULL)
         return -1;
 
-      len = _vsnprintf (p, bufsize - 1, format, args);
+      DBUS_VA_COPY (args_copy, args);
+      len = _vsnprintf (p, bufsize - 1, format, args_copy);
+      va_end (args_copy);
       free (p);
     }