dix: integer overflow in REQUEST_FIXED_SIZE() [CVE-2014-8092 4/4]

Force use of 64-bit integers when evaluating data provided by clients
in 32-bit fields which can overflow when added or multiplied during
checks.

Reported-by: Ilja Van Sprundel <ivansprundel@ioactive.com>
Signed-off-by: Alan Coopersmith <alan.coopersmith@oracle.com>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>

include/dix.h

@@ -76,7 +76,8 @@ SOFTWARE.
 
 #define REQUEST_FIXED_SIZE(req, n)\
     if (((sizeof(req) >> 2) > client->req_len) || \
-        (((sizeof(req) + (n) + 3) >> 2) != client->req_len)) \
+        ((n >> 2) >= client->req_len) || \
+        ((((uint64_t) sizeof(req) + (n) + 3) >> 2) != (uint64_t) client->req_len))  \
          return(BadLength)
 
 #define LEGAL_NEW_RESOURCE(id,client)\