Merge branch 'PHP-7.1' into PHP-7.2

* PHP-7.1:
  Fix bug #77950 - Heap-buffer-overflow in _estrndup via exif_process_IFD_TAG

Author: smalyshev

ext/exif/exif.c

@@ -3304,7 +3304,7 @@ static int exif_process_IFD_TAG(image_info_type *ImageInfo, char *dir_entry, cha
             offset_base is ImageInfo->file.list[sn].data-dir_offset
             dir_entry - offset_base is dir_offset+2+i*12
         */
-		if (byte_count > IFDlength || offset_val > IFDlength-byte_count || value_ptr < dir_entry || offset_val < (size_t)(dir_entry-offset_base)) {
+		if (byte_count > IFDlength || offset_val > IFDlength-byte_count || value_ptr < dir_entry || offset_val < (size_t)(dir_entry-offset_base) || dir_entry <= offset_base) {
 			/* It is important to check for IMAGE_FILETYPE_TIFF
 			 * JPEG does not use absolute pointers instead its pointers are
 			 * relative to the start of the TIFF header in APP1 section. */

ext/exif/tests/bug77950.phpt

@@ -0,0 +1,12 @@
+--TEST--
+Bug #77950 (Heap-buffer-overflow in _estrndup via exif_process_IFD_TAG)
+--SKIPIF--
+<?php if (!extension_loaded('exif')) print 'skip exif extension not available';?>
+--FILE--
+<?php
+exif_read_data(__DIR__."/bug77950.tiff");
+?>
+DONE
+--EXPECTF--
+%A
+DONE