From 435e21f05001fb03f9f186fa7cbc69454afd00d1 Mon Sep 17 00:00:00 2001
From: Dan Fandrich <dan@coneharvesters.com>
Date: Sat, 16 May 2020 17:32:28 +0200
Subject: [PATCH] Fix MakerNote tag size overflow issues at read time.

Check for a size overflow while reading tags, which ensures that the
size is always consistent for the given components and type of the
entry, making checking further down superfluous.

This provides an alternate fix for
https://sourceforge.net/p/libexif/bugs/125/ CVE-2016-6328 and for all
the MakerNote types. Likely, this makes both commits 41bd0423 and
89e5b1c1 redundant as it ensures that MakerNote entries are well-formed
when they're populated.

Some improvements on top by Marcus Meissner <marcus@jet.franken.de>

CVE-2020-13112
---
 libexif/canon/exif-mnote-data-canon.c     | 19 +++++++++++++++---
 libexif/fuji/exif-mnote-data-fuji.c       | 23 ++++++++++++++++------
 libexif/olympus/exif-mnote-data-olympus.c | 24 ++++++++++++++++-------
 libexif/pentax/exif-mnote-data-pentax.c   | 18 +++++++++++++----
 4 files changed, 64 insertions(+), 20 deletions(-)

diff --git a/libexif/canon/exif-mnote-data-canon.c b/libexif/canon/exif-mnote-data-canon.c
index 9cea4e4..9cfe781 100644
--- a/libexif/canon/exif-mnote-data-canon.c
+++ b/libexif/canon/exif-mnote-data-canon.c
@@ -35,6 +35,8 @@
 /* Total size limit to prevent abuse by DoS */
 #define FAILSAFE_SIZE_MAX 1000000L
 
+#define CHECKOVERFLOW(offset,datasize,structsize) (( offset >= datasize) || (structsize > datasize) || (offset > datasize - structsize ))
+	
 static void
 exif_mnote_data_canon_clear (ExifMnoteDataCanon *n)
 {
@@ -213,7 +215,7 @@ exif_mnote_data_canon_load (ExifMnoteData *ne,
 		return;
 	}
 	datao = 6 + n->offset;
-	if ((datao + 2 < datao) || (datao + 2 < 2) || (datao + 2 > buf_size)) {
+	if (CHECKOVERFLOW(datao, buf_size, 2)) {
 		exif_log (ne->log, EXIF_LOG_CODE_CORRUPT_DATA,
 			  "ExifMnoteCanon", "Short MakerNote");
 		return;
@@ -238,7 +240,7 @@ exif_mnote_data_canon_load (ExifMnoteData *ne,
 	for (i = c, o = datao; i; --i, o += 12) {
 		size_t s;
 		memset(&n->entries[tcount], 0, sizeof(MnoteCanonEntry));
-		if ((o + 12 < o) || (o + 12 < 12) || (o + 12 > buf_size)) {
+		if (CHECKOVERFLOW(o,buf_size,12)) {
 			exif_log (ne->log, EXIF_LOG_CODE_CORRUPT_DATA,
 				"ExifMnoteCanon", "Short MakerNote");
 			break;
@@ -253,6 +255,16 @@ exif_mnote_data_canon_load (ExifMnoteData *ne,
 			"Loading entry 0x%x ('%s')...", n->entries[tcount].tag,
 			 mnote_canon_tag_get_name (n->entries[tcount].tag));
 
+		/* Check if we overflow the multiplication. Use buf_size as the max size for integer overflow detection,
+		 * we will check the buffer sizes closer later. */
+		if (	exif_format_get_size (n->entries[tcount].format) &&
+			buf_size / exif_format_get_size (n->entries[tcount].format) < n->entries[tcount].components
+		) {
+			exif_log (ne->log, EXIF_LOG_CODE_CORRUPT_DATA,
+				  "ExifMnoteCanon", "Tag size overflow detected (%u * %lu)", exif_format_get_size (n->entries[tcount].format), n->entries[tcount].components);
+			continue;
+		}
+
 		/*
 		 * Size? If bigger than 4 bytes, the actual data is not
 		 * in the entry but somewhere else (offset).
@@ -269,7 +281,8 @@ exif_mnote_data_canon_load (ExifMnoteData *ne,
 		} else {
 			size_t dataofs = o + 8;
 			if (s > 4) dataofs = exif_get_long (buf + dataofs, n->order) + 6;
-			if ((dataofs + s < s) || (dataofs + s < dataofs) || (dataofs + s > buf_size)) {
+
+			if (CHECKOVERFLOW(dataofs, buf_size, s)) {
 				exif_log (ne->log, EXIF_LOG_CODE_DEBUG,
 					"ExifMnoteCanon",
 					"Tag data past end of buffer (%u > %u)",
diff --git a/libexif/fuji/exif-mnote-data-fuji.c b/libexif/fuji/exif-mnote-data-fuji.c
index efcf654..08bee21 100644
--- a/libexif/fuji/exif-mnote-data-fuji.c
+++ b/libexif/fuji/exif-mnote-data-fuji.c
@@ -28,6 +28,8 @@
 
 #include "exif-mnote-data-fuji.h"
 
+#define CHECKOVERFLOW(offset,datasize,structsize) (( offset >= datasize) || (structsize > datasize) || (offset > datasize - structsize ))
+
 struct _MNoteFujiDataPrivate {
 	ExifByteOrder order;
 };
@@ -162,16 +164,16 @@ exif_mnote_data_fuji_load (ExifMnoteData *en,
 		return;
 	}
 	datao = 6 + n->offset;
-	if ((datao + 12 < datao) || (datao + 12 < 12) || (datao + 12 > buf_size)) {
+	if (CHECKOVERFLOW(datao, buf_size, 12)) {
 		exif_log (en->log, EXIF_LOG_CODE_CORRUPT_DATA,
 			  "ExifMnoteDataFuji", "Short MakerNote");
 		return;
 	}
 
 	n->order = EXIF_BYTE_ORDER_INTEL;
+
 	datao += exif_get_long (buf + datao + 8, EXIF_BYTE_ORDER_INTEL);
-	if ((datao + 2 < datao) || (datao + 2 < 2) ||
-	    (datao + 2 > buf_size)) {
+	if (CHECKOVERFLOW(datao, buf_size, 2)) {
 		exif_log (en->log, EXIF_LOG_CODE_CORRUPT_DATA,
 			  "ExifMnoteDataFuji", "Short MakerNote");
 		return;
@@ -195,8 +197,9 @@ exif_mnote_data_fuji_load (ExifMnoteData *en,
 	tcount = 0;
 	for (i = c, o = datao; i; --i, o += 12) {
 		size_t s;
+
 		memset(&n->entries[tcount], 0, sizeof(MnoteFujiEntry));
-		if ((o + 12 < o) || (o + 12 < 12) || (o + 12 > buf_size)) {
+		if (CHECKOVERFLOW(o, buf_size, 12)) {
 			exif_log (en->log, EXIF_LOG_CODE_CORRUPT_DATA,
 				  "ExifMnoteDataFuji", "Short MakerNote");
 			break;
@@ -211,6 +214,15 @@ exif_mnote_data_fuji_load (ExifMnoteData *en,
 			  "Loading entry 0x%x ('%s')...", n->entries[tcount].tag,
 			  mnote_fuji_tag_get_name (n->entries[tcount].tag));
 
+		/* Check if we overflow the multiplication. Use buf_size as the max size for integer overflow detection,
+		 * we will check the buffer sizes closer later. */
+		if (	exif_format_get_size (n->entries[tcount].format) &&
+			buf_size / exif_format_get_size (n->entries[tcount].format) < n->entries[tcount].components
+		) {
+			exif_log (en->log, EXIF_LOG_CODE_CORRUPT_DATA,
+					  "ExifMnoteDataFuji", "Tag size overflow detected (%u * %lu)", exif_format_get_size (n->entries[tcount].format), n->entries[tcount].components);
+			continue;
+		}
 		/*
 		 * Size? If bigger than 4 bytes, the actual data is not
 		 * in the entry but somewhere else (offset).
@@ -222,8 +234,7 @@ exif_mnote_data_fuji_load (ExifMnoteData *en,
 			if (s > 4)
 				/* The data in this case is merely a pointer */
 				dataofs = exif_get_long (buf + dataofs, n->order) + 6 + n->offset;
-			if ((dataofs + s < dataofs) || (dataofs + s < s) ||
-				(dataofs + s >= buf_size)) {
+			if (CHECKOVERFLOW(dataofs, buf_size, s)) {
 				exif_log (en->log, EXIF_LOG_CODE_CORRUPT_DATA,
 						  "ExifMnoteDataFuji", "Tag data past end of "
 					  "buffer (%u >= %u)", dataofs + s, buf_size);
diff --git a/libexif/olympus/exif-mnote-data-olympus.c b/libexif/olympus/exif-mnote-data-olympus.c
index 9bf0855..45e4bc5 100644
--- a/libexif/olympus/exif-mnote-data-olympus.c
+++ b/libexif/olympus/exif-mnote-data-olympus.c
@@ -37,6 +37,8 @@
  */
 /*#define EXIF_OVERCOME_SANYO_OFFSET_BUG */
 
+#define CHECKOVERFLOW(offset,datasize,structsize) (( offset >= datasize) || (structsize > datasize) || (offset > datasize - structsize ))
+
 static enum OlympusVersion
 exif_mnote_data_olympus_identify_variant (const unsigned char *buf,
 		unsigned int buf_size);
@@ -247,7 +249,7 @@ exif_mnote_data_olympus_load (ExifMnoteData *en,
 		return;
 	}
 	o2 = 6 + n->offset; /* Start of interesting data */
-	if ((o2 + 10 < o2) || (o2 + 10 < 10) || (o2 + 10 > buf_size)) {
+	if (CHECKOVERFLOW(o2,buf_size,10)) {
 		exif_log (en->log, EXIF_LOG_CODE_CORRUPT_DATA,
 			  "ExifMnoteDataOlympus", "Short MakerNote");
 		return;
@@ -303,6 +305,7 @@ exif_mnote_data_olympus_load (ExifMnoteData *en,
 		/* Olympus S760, S770 */
 		datao = o2;
 		o2 += 8;
+		if (CHECKOVERFLOW(o2,buf_size,4)) return;
 		exif_log (en->log, EXIF_LOG_CODE_DEBUG, "ExifMnoteDataOlympus",
 			"Parsing Olympus maker note v2 (0x%02x, %02x, %02x, %02x)...",
 			buf[o2], buf[o2 + 1], buf[o2 + 2], buf[o2 + 3]);
@@ -346,7 +349,7 @@ exif_mnote_data_olympus_load (ExifMnoteData *en,
 
 	case nikonV2:
 		o2 += 6;
-		if (o2 >= buf_size) return;
+		if (CHECKOVERFLOW(o2,buf_size,12)) return;
 		exif_log (en->log, EXIF_LOG_CODE_DEBUG, "ExifMnoteDataOlympus",
 			"Parsing Nikon maker note v2 (0x%02x, %02x, %02x, "
 			"%02x, %02x, %02x, %02x, %02x)...",
@@ -406,7 +409,7 @@ exif_mnote_data_olympus_load (ExifMnoteData *en,
 	}
 
 	/* Sanity check the offset */
-	if ((o2 + 2 < o2) || (o2 + 2 < 2) || (o2 + 2 > buf_size)) {
+	if (CHECKOVERFLOW(o2,buf_size,2)) {
 		exif_log (en->log, EXIF_LOG_CODE_CORRUPT_DATA,
 			  "ExifMnoteOlympus", "Short MakerNote");
 		return;
@@ -431,7 +434,7 @@ exif_mnote_data_olympus_load (ExifMnoteData *en,
 	for (i = c, o = o2; i; --i, o += 12) {
 		size_t s;
 		memset(&n->entries[tcount], 0, sizeof(MnoteOlympusEntry));
-		if ((o + 12 < o) || (o + 12 < 12) || (o + 12 > buf_size)) {
+		if (CHECKOVERFLOW(o, buf_size, 12)) {
 			exif_log (en->log, EXIF_LOG_CODE_CORRUPT_DATA,
 				  "ExifMnoteOlympus", "Short MakerNote");
 			break;
@@ -452,6 +455,14 @@ exif_mnote_data_olympus_load (ExifMnoteData *en,
 		    n->entries[tcount].components,
 		    (int)exif_format_get_size(n->entries[tcount].format)); */
 
+	    /* Check if we overflow the multiplication. Use buf_size as the max size for integer overflow detection,
+	     * we will check the buffer sizes closer later. */
+	    if (exif_format_get_size (n->entries[tcount].format) &&
+		buf_size / exif_format_get_size (n->entries[tcount].format) < n->entries[tcount].components
+	    ) {
+		exif_log (en->log, EXIF_LOG_CODE_CORRUPT_DATA, "ExifMnoteOlympus", "Tag size overflow detected (%u * %lu)", exif_format_get_size (n->entries[tcount].format), n->entries[tcount].components);
+		continue;
+	    }
 	    /*
 	     * Size? If bigger than 4 bytes, the actual data is not
 	     * in the entry but somewhere else (offset).
@@ -470,7 +481,7 @@ exif_mnote_data_olympus_load (ExifMnoteData *en,
 				 * tag in its MakerNote. The offset is actually the absolute
 				 * position in the file instead of the position within the IFD.
 				 */
-			    if (dataofs + s > buf_size && n->version == sanyoV1) {
+			    if (dataofs > (buf_size - s) && n->version == sanyoV1) {
 					/* fix pointer */
 					dataofs -= datao + 6;
 					exif_log (en->log, EXIF_LOG_CODE_DEBUG,
@@ -479,8 +490,7 @@ exif_mnote_data_olympus_load (ExifMnoteData *en,
 			    }
 #endif
 			}
-			if ((dataofs + s < dataofs) || (dataofs + s < s) || 
-			    (dataofs + s > buf_size)) {
+			if (CHECKOVERFLOW(dataofs, buf_size, s)) {
 				exif_log (en->log, EXIF_LOG_CODE_DEBUG,
 					  "ExifMnoteOlympus",
 					  "Tag data past end of buffer (%u > %u)",
diff --git a/libexif/pentax/exif-mnote-data-pentax.c b/libexif/pentax/exif-mnote-data-pentax.c
index 1de77b8..7312827 100644
--- a/libexif/pentax/exif-mnote-data-pentax.c
+++ b/libexif/pentax/exif-mnote-data-pentax.c
@@ -28,6 +28,8 @@
 #include <libexif/exif-byte-order.h>
 #include <libexif/exif-utils.h>
 
+#define CHECKOVERFLOW(offset,datasize,structsize) (( offset >= datasize) || (structsize > datasize) || (offset > datasize - structsize ))
+
 static void
 exif_mnote_data_pentax_clear (ExifMnoteDataPentax *n)
 {
@@ -224,7 +226,7 @@ exif_mnote_data_pentax_load (ExifMnoteData *en,
 		return;
 	}
 	datao = 6 + n->offset;
-	if ((datao + 8 < datao) || (datao + 8 < 8) || (datao + 8 > buf_size)) {
+	if (CHECKOVERFLOW(datao, buf_size, 8)) {
 		exif_log (en->log, EXIF_LOG_CODE_CORRUPT_DATA,
 			  "ExifMnoteDataPentax", "Short MakerNote");
 		return;
@@ -278,7 +280,7 @@ exif_mnote_data_pentax_load (ExifMnoteData *en,
 	for (i = c, o = datao; i; --i, o += 12) {
 		size_t s;
 		memset(&n->entries[tcount], 0, sizeof(MnotePentaxEntry));
-		if ((o + 12 < o) || (o + 12 < 12) || (o + 12 > buf_size)) {
+		if (CHECKOVERFLOW(o,buf_size,12)) {
 			exif_log (en->log, EXIF_LOG_CODE_CORRUPT_DATA,
 				  "ExifMnoteDataPentax", "Short MakerNote");
 			break;
@@ -293,6 +295,15 @@ exif_mnote_data_pentax_load (ExifMnoteData *en,
 			  "Loading entry 0x%x ('%s')...", n->entries[tcount].tag,
 			  mnote_pentax_tag_get_name (n->entries[tcount].tag));
 
+		/* Check if we overflow the multiplication. Use buf_size as the max size for integer overflow detection,
+		 * we will check the buffer sizes closer later. */
+		if (	exif_format_get_size (n->entries[tcount].format) &&
+			buf_size / exif_format_get_size (n->entries[tcount].format) < n->entries[tcount].components
+		) {
+			exif_log (en->log, EXIF_LOG_CODE_CORRUPT_DATA,
+				  "ExifMnoteDataPentax", "Tag size overflow detected (%u * %lu)", exif_format_get_size (n->entries[tcount].format), n->entries[tcount].components);
+			break;
+		}
 		/*
 		 * Size? If bigger than 4 bytes, the actual data is not
 		 * in the entry but somewhere else (offset).
@@ -305,8 +316,7 @@ exif_mnote_data_pentax_load (ExifMnoteData *en,
 			if (s > 4)
 				/* The data in this case is merely a pointer */
 			   	dataofs = exif_get_long (buf + dataofs, n->order) + 6;
-			if ((dataofs + s < dataofs) || (dataofs + s < s) ||
-				(dataofs + s > buf_size)) {
+			if (CHECKOVERFLOW(dataofs, buf_size, s)) {
 				exif_log (en->log, EXIF_LOG_CODE_DEBUG,
 						  "ExifMnoteDataPentax", "Tag data past end "
 					  "of buffer (%u > %u)", dataofs + s, buf_size);
-- 
2.27.0

