From ce03ad7ef4e8aeefce79192bf5b6f69fae396f0c Mon Sep 17 00:00:00 2001
From: Marcus Meissner <marcus@jet.franken.de>
Date: Mon, 8 Jun 2020 17:27:06 +0200
Subject: [PATCH] fixed another unsigned integer overflow

first fixed by google in android fork,
https://android.googlesource.com/platform/external/libexif/+/1e187b62682ffab5003c702657d6d725b4278f16%5E%21/#F0

(use a more generic overflow check method, also check second overflow instance.)

https://security-tracker.debian.org/tracker/CVE-2020-0198
---
 libexif/exif-data.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/libexif/exif-data.c b/libexif/exif-data.c
index 8b280d3a..b495726d 100644
--- a/libexif/exif-data.c
+++ b/libexif/exif-data.c
@@ -47,6 +47,8 @@
 #undef JPEG_MARKER_APP1
 #define JPEG_MARKER_APP1 0xe1
 
+#define CHECKOVERFLOW(offset,datasize,structsize) (( offset >= datasize) || (structsize > datasize) || (offset > datasize - structsize ))
+
 static const unsigned char ExifHeader[] = {0x45, 0x78, 0x69, 0x66, 0x00, 0x00};
 
 struct _ExifDataPrivate
@@ -327,7 +329,7 @@ exif_data_load_data_thumbnail (ExifData *data, const unsigned char *d,
 		exif_log (data->priv->log, EXIF_LOG_CODE_DEBUG, "ExifData", "Bogus thumbnail offset (%u).", o);
 		return;
 	}
-	if (s > ds - o) {
+	if (CHECKOVERFLOW(o,ds,s)) {
 		exif_log (data->priv->log, EXIF_LOG_CODE_DEBUG, "ExifData", "Bogus thumbnail size (%u), max would be %u.", s, ds-o);
 		return;
 	}
@@ -420,9 +422,9 @@ exif_data_load_data_content (ExifData *data, ExifIfd ifd,
 	}
 
 	/* Read the number of entries */
-	if ((offset + 2 < offset) || (offset + 2 < 2) || (offset + 2 > ds)) {
+	if (CHECKOVERFLOW(offset, ds, 2)) {
 		exif_log (data->priv->log, EXIF_LOG_CODE_CORRUPT_DATA, "ExifData",
-			  "Tag data past end of buffer (%u > %u)", offset+2, ds);
+			  "Tag data past end of buffer (%u+2 > %u)", offset, ds);
 		return;
 	}
 	n = exif_get_short (d + offset, data->priv->order);
@@ -431,7 +433,7 @@ exif_data_load_data_content (ExifData *data, ExifIfd ifd,
 	offset += 2;
 
 	/* Check if we have enough data. */
-	if (offset + 12 * n > ds) {
+	if (CHECKOVERFLOW(offset, ds, 12*n)) {
 		n = (ds - offset) / 12;
 		exif_log (data->priv->log, EXIF_LOG_CODE_DEBUG, "ExifData",
 				  "Short data; only loading %hu entries...", n);
