Fix bug #77988 - heap-buffer-overflow on php_jpg_get16

Author: smalyshev

ext/exif/exif.c

@@ -3540,6 +3540,8 @@ static int exif_scan_thumbnail(image_info_type *ImageInfo TSRMLS_DC)
 		if (c == 0xFF)
 			return FALSE;
 		marker = c;
+		if (pos>=ImageInfo->Thumbnail.size)
+			return FALSE;
 		length = php_jpg_get16(data+pos);
 		if (length > ImageInfo->Thumbnail.size || pos >= ImageInfo->Thumbnail.size - length) {
 			return FALSE;

ext/exif/tests/bug77988.jpg

@@ -0,0 +1,11 @@
+--TEST--
+Bug #77988 (heap-buffer-overflow on php_jpg_get16)
+--SKIPIF--
+<?php if (!extension_loaded('exif')) print 'skip exif extension not available';?>
+--FILE--
+<?php
+exif_read_data(__DIR__."/bug77988.jpg", 'COMMENT', FALSE, TRUE);
+?>
+DONE
+--EXPECTF--
+DONE