From f80ad18afae2230c2c1802c7d829100af646874e Mon Sep 17 00:00:00 2001
From: Stanislav Malyshev <stas@php.net>
Date: Mon, 29 Apr 2019 23:38:12 -0700
Subject: [PATCH] Fix bug #77950 - Heap-buffer-overflow in _estrndup via
 exif_process_IFD_TAG

I do not completely understand what is going on there, but I am pretty
sure dir_entry <= offset_base if not a normal situation, so we better not
to rely on such dir_entry.
---
 ext/exif/exif.c              |   2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/ext/exif/exif.c b/ext/exif/exif.c
index a763f6c..d174def 100644
--- a/ext/exif/exif.c
+++ b/ext/exif/exif.c
@@ -2891,7 +2891,7 @@ 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. */