[psaux] Fix potential buffer overflow (#45922).

* src/psaux/psobjs.c (ps_parser_skip_PS_token): If a token is
enclosed in balanced expressions, ensure that the cursor position
doesn't get larger than the current limit.

ChangeLog

@@ -1,3 +1,11 @@
+2015-09-11  Werner Lemberg  <wl@gnu.org>
+
+	[psaux] Fix potential buffer overflow (#45922).
+
+	* src/psaux/psobjs.c (ps_parser_skip_PS_token): If a token is
+	enclosed in balanced expressions, ensure that the cursor position
+	doesn't get larger than the current limit.
+
 2015-09-11  Werner Lemberg  <wl@gnu.org>
 
 	[base] Avoid crash while tracing `load_mac_face'.

src/psaux/psobjs.c

@@ -594,6 +594,9 @@
       error = FT_THROW( Invalid_File_Format );
     }
 
+    if ( cur > limit )
+      cur = limit;
+
     parser->error  = error;
     parser->cursor = cur;
   }