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

(cherry picked from commit 73ff419)

Author: smalyshev

NEWS

@@ -6,6 +6,10 @@ PHP                                                                        NEWS
   . Implemented FR #72189 (Add missing CURL_VERSION_* constants). (Javier
     Spagnoletti)
 
+- EXIF:
+  . Fixed bug #77988 (heap-buffer-overflow on php_jpg_get16).
+    (CVE-2019-11040) (Stas)
+
 - FPM:
   . Fixed bug #77934 (php-fpm kill -USR2 not working). (Jakub Zelenka)
   . Fixed bug #77921 (static.php.net doesn't work anymore). (Peter Kokot)

ext/exif/exif.c

@@ -3920,6 +3920,8 @@ static int exif_scan_thumbnail(image_info_type *ImageInfo)
 		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