Fix bug #72730 - imagegammacorrect allows arbitrary write access

ext/gd/gd.c

@@ -3082,6 +3082,11 @@ PHP_FUNCTION(imagegammacorrect)
 		return;
 	}
 
+	if ( input <= 0.0 || output <= 0.0 ) {
+		php_error_docref(NULL TSRMLS_CC, E_WARNING, "Gamma values should be positive");
+		RETURN_FALSE;
+	}
+
 	ZEND_FETCH_RESOURCE(im, gdImagePtr, &IM, -1, "Image", le_gd);
 
 	if (gdImageTrueColor(im))	{

ext/gd/tests/bug72730.phpt

@@ -0,0 +1,15 @@
+--TEST--
+Bug #72730: imagegammacorrect allows arbitrary write access
+--SKIPIF--
+<?php 
+if (!function_exists("imagecreatetruecolor")) die("skip");
+?>
+--FILE--
+<?php
+$img =  imagecreatetruecolor(1, 1);
+imagegammacorrect($img, -1, 1337);
+?>
+DONE
+--EXPECTF--
+Warning: imagegammacorrect(): Gamma values should be positive in %sbug72730.php on line %d
+DONE