From 0a05ba257b6ddd87dacf8d54b626e4b360e0a596 Mon Sep 17 00:00:00 2001
From: Werner Lemberg <wl@gnu.org>
Date: Fri, 20 Mar 2009 07:19:45 +0100
Subject: [PATCH] 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         | 9 +++++++++
 src/lzw/ftzopen.c | 3 +++
 2 files changed, 12 insertions(+)

diff --git a/ChangeLog b/ChangeLog
index 512d99ccd..f208f51ec 100644
--- a/ChangeLog
+++ b/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.
diff --git a/src/lzw/ftzopen.c b/src/lzw/ftzopen.c
index fc7831510..c0483de62 100644
--- a/src/lzw/ftzopen.c
+++ b/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];
           }