Vulnerability: In libexif, there is a possible out of bounds write due to an integer overflow. This could lead to remote escalation of privilege in the media content provider with no additional execution privileges needed. User interaction is needed for exploitation. Product: AndroidVersions: Android-10Android ID: A-112537774
Vulnerability ID: CVE-2019-9278
CWE: CWE-787
Severity score: 6.4
Project: https://github.com/libexif/libexif
Published: 2019-09-27
File: libexif/exif-data.c
Commit message: fix CVE-2019-9278

avoid the use of unsafe integer overflow checking constructs (unsigned integer operations cannot overflow, so "u1 + u2 > u1" can be optimized away)

check for the actual sizes, which should also handle the overflows
document other places google patched, but do not seem relevant due to other restrictions

fixes https://github.com/libexif/libexif/issues/26
Commit author: Marcus Meissner

Vulnerable version (before fix):
 exif_data_load_data_entry (ExifData *data, ExifEntry *entry, 		doff = offset + 8;  	/* Sanity checks */ 	if ((doff + s < doff) || (doff + s < s) || (doff + s > size)) { 		exif_log (data->priv->log, EXIF_LOG_CODE_DEBUG, "ExifData", 				  "Tag data past end of buffer (%u > %u)", doff+s, size);	 		return 0; 	}  exif_data_load_data_thumbnail (ExifData *data, const unsigned char *d, 			       unsigned int ds, ExifLong o, ExifLong s) { 	/* Sanity checks */ 	if ((o + s < o) || (o + s < s) || (o + s > ds) || (o > ds)) { 		exif_log (data->priv->log, EXIF_LOG_CODE_DEBUG, "ExifData", 			  "Bogus thumbnail offset (%u) or size (%u).", 			  o, s); 		return; 	}  	if (data->data)  		exif_mem_free (data->priv->mem, data->data); 	if (!(data->data = exif_data_alloc (data, s))) { exif_data_load_data (ExifData *data, const unsigned char *d_orig, 	exif_log (data->priv->log, EXIF_LOG_CODE_DEBUG, "ExifData",  		  "IFD 0 at %i.", (int) offset);  	/* Sanity check the offset, being careful about overflow */ 	if (offset > ds || offset + 6 + 2 > ds) 		return;  exif_data_load_data (ExifData *data, const unsigned char *d_orig,  	/* IFD 1 offset */ 	n = exif_get_short (d + 6 + offset, data->priv->order); 	if (offset + 6 + 2 + 12 * n + 4 > ds) 		return;  exif_data_load_data (ExifData *data, const unsigned char *d_orig, 		exif_log (data->priv->log, EXIF_LOG_CODE_DEBUG, "ExifData", 			  "IFD 1 at %i.", (int) offset);  		/* Sanity check. */ 		if (offset > ds || offset + 6 > ds) { 			exif_log (data->priv->log, EXIF_LOG_CODE_CORRUPT_DATA, 				  "ExifData", "Bogus offset of IFD1."); 		} else {

Fixed version (after fix):
 exif_data_load_data_entry (ExifData *data, ExifEntry *entry, 		doff = offset + 8;  	/* Sanity checks */ 	if (doff >= size) { 		exif_log (data->priv->log, EXIF_LOG_CODE_DEBUG, "ExifData", 				  "Tag starts past end of buffer (%u > %u)", doff, size); 		return 0; 	}  	if (s > size - doff) { 		exif_log (data->priv->log, EXIF_LOG_CODE_DEBUG, "ExifData", 				  "Tag data goes past end of buffer (%u > %u)", doff+s, size); 		return 0; 	}  exif_data_load_data_thumbnail (ExifData *data, const unsigned char *d, 			       unsigned int ds, ExifLong o, ExifLong s) { 	/* Sanity checks */ 	if (o >= ds) { 		exif_log (data->priv->log, EXIF_LOG_CODE_DEBUG, "ExifData", "Bogus thumbnail offset (%u).", o); 		return; 	} 	if (s > ds - o) { 		exif_log (data->priv->log, EXIF_LOG_CODE_DEBUG, "ExifData", "Bogus thumbnail size (%u), max would be %u.", s, ds-o); 		return; 	} 	if (data->data)  		exif_mem_free (data->priv->mem, data->data); 	if (!(data->data = exif_data_alloc (data, s))) { exif_data_load_data (ExifData *data, const unsigned char *d_orig, 	exif_log (data->priv->log, EXIF_LOG_CODE_DEBUG, "ExifData",  		  "IFD 0 at %i.", (int) offset);  	/* ds is restricted to 16 bit above, so offset is restricted too, and offset+8 should not overflow. */ 	if (offset > ds || offset + 6 + 2 > ds) 		return;  exif_data_load_data (ExifData *data, const unsigned char *d_orig,  	/* IFD 1 offset */ 	n = exif_get_short (d + 6 + offset, data->priv->order); 	/* offset < 2<<16, n is 16 bit at most, so this op will not overflow */ 	if (offset + 6 + 2 + 12 * n + 4 > ds) 		return;  exif_data_load_data (ExifData *data, const unsigned char *d_orig, 		exif_log (data->priv->log, EXIF_LOG_CODE_DEBUG, "ExifData", 			  "IFD 1 at %i.", (int) offset);  		/* Sanity check. ds is ensured to be above 6 above, offset is 16bit */ 		if (offset > ds - 6) { 			exif_log (data->priv->log, EXIF_LOG_CODE_CORRUPT_DATA, 				  "ExifData", "Bogus offset of IFD1."); 		} else {

Patch:
patch: @@ -192,9 +192,15 @@ exif_data_load_data_entry (ExifData *data, ExifEntry *entry,
 		doff = offset + 8;
 
 	/* Sanity checks */
-	if ((doff + s < doff) || (doff + s < s) || (doff + s > size)) {
+	if (doff >= size) {
 		exif_log (data->priv->log, EXIF_LOG_CODE_DEBUG, "ExifData",
-				  "Tag data past end of buffer (%u > %u)", doff+s, size);	
+				  "Tag starts past end of buffer (%u > %u)", doff, size);
+		return 0;
+	}
+
+	if (s > size - doff) {
+		exif_log (data->priv->log, EXIF_LOG_CODE_DEBUG, "ExifData",
+				  "Tag data goes past end of buffer (%u > %u)", doff+s, size);
 		return 0;
 	}
 
@@ -315,13 +321,14 @@ exif_data_load_data_thumbnail (ExifData *data, const unsigned char *d,
 			       unsigned int ds, ExifLong o, ExifLong s)
 {
 	/* Sanity checks */
-	if ((o + s < o) || (o + s < s) || (o + s > ds) || (o > ds)) {
-		exif_log (data->priv->log, EXIF_LOG_CODE_DEBUG, "ExifData",
-			  "Bogus thumbnail offset (%u) or size (%u).",
-			  o, s);
+	if (o >= ds) {
+		exif_log (data->priv->log, EXIF_LOG_CODE_DEBUG, "ExifData", "Bogus thumbnail offset (%u).", o);
+		return;
+	}
+	if (s > ds - o) {
+		exif_log (data->priv->log, EXIF_LOG_CODE_DEBUG, "ExifData", "Bogus thumbnail size (%u), max would be %u.", s, ds-o);
 		return;
 	}
-
 	if (data->data) 
 		exif_mem_free (data->priv->mem, data->data);
 	if (!(data->data = exif_data_alloc (data, s))) {
@@ -947,7 +954,7 @@ exif_data_load_data (ExifData *data, const unsigned char *d_orig,
 	exif_log (data->priv->log, EXIF_LOG_CODE_DEBUG, "ExifData", 
 		  "IFD 0 at %i.", (int) offset);
 
-	/* Sanity check the offset, being careful about overflow */
+	/* ds is restricted to 16 bit above, so offset is restricted too, and offset+8 should not overflow. */
 	if (offset > ds || offset + 6 + 2 > ds)
 		return;
 
@@ -956,6 +963,7 @@ exif_data_load_data (ExifData *data, const unsigned char *d_orig,
 
 	/* IFD 1 offset */
 	n = exif_get_short (d + 6 + offset, data->priv->order);
+	/* offset < 2<<16, n is 16 bit at most, so this op will not overflow */
 	if (offset + 6 + 2 + 12 * n + 4 > ds)
 		return;
 
@@ -964,8 +972,8 @@ exif_data_load_data (ExifData *data, const unsigned char *d_orig,
 		exif_log (data->priv->log, EXIF_LOG_CODE_DEBUG, "ExifData",
 			  "IFD 1 at %i.", (int) offset);
 
-		/* Sanity check. */
-		if (offset > ds || offset + 6 > ds) {
+		/* Sanity check. ds is ensured to be above 6 above, offset is 16bit */
+		if (offset > ds - 6) {
 			exif_log (data->priv->log, EXIF_LOG_CODE_CORRUPT_DATA,
 				  "ExifData", "Bogus offset of IFD1.");
 		} else {
path: libexif/exif-data.c