Protect against malformed compressed data.

Problem reported by Tavis Ormandy <taviso@google.com>.

* src/lsw/ftzopen.c (ft_lzwstate_io): Test whether `state->prefix' is
zero.

ChangeLog

@@ -1,3 +1,12 @@
+2009-03-20  Werner Lemberg  <wl@gnu.org>
+
+	Protect against malformed compressed data.
+
+	Problem reported by Tavis Ormandy <taviso@google.com>.
+
+	* src/lsw/ftzopen.c (ft_lzwstate_io): Test whether `state->prefix' is
+	zero.
+
 2009-03-20  Werner Lemberg  <wl@gnu.org>
 
 	Protect against invalid SID values in CFFs.

src/lzw/ftzopen.c

@@ -332,6 +332,9 @@
 
           while ( code >= 256U )
           {
+            if ( !state->prefix )
+              goto Eof;
+
             FTLZW_STACK_PUSH( state->suffix[code - 256] );
             code = state->prefix[code - 256];
           }