From 5f46d2f08eda1b81b09264e12b2fdf4a16342e2f Mon Sep 17 00:00:00 2001
From: dgp <dgp@users.sourceforge.net>
Date: Fri, 15 May 2015 12:03:25 +0000
Subject: Use assertion to prevent writing pixel lines beyond end of Photo
 image block.

---
 generic/tkImgPNG.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/generic/tkImgPNG.c b/generic/tkImgPNG.c
index d6a706a..8146e33 100644
--- a/generic/tkImgPNG.c
+++ b/generic/tkImgPNG.c
@@ -10,6 +10,7 @@
  * this file, and for a DISCLAIMER OF ALL WARRANTIES.
  */
 
+#include "assert.h"
 #include "tkInt.h"
 
 #define	PNG_INT32(a,b,c,d)	\
@@ -1880,6 +1881,8 @@ DecodeLine(
      * Calculate offset into pixelPtr for the first pixel of the line.
      */
 
+    assert(pngPtr->currentLine < pngPtr->block.height);
+
     offset = pngPtr->currentLine * pngPtr->block.pitch;
 
     /*
-- 
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