udf_get_extendedattr() had no boundary checks.

When parsing the ExtendedAttr data, malicous or corrupt attribute length
could cause kernel hangs and buffer overruns in some special cases.

Link: https://lore.kernel.org/r/20210822093332.25234-1-stian.skjelstad@gmail.com
Signed-off-by: Stian Skjelstad <stian.skjelstad@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>

fs/udf/misc.c

@@ -173,13 +173,22 @@ struct genericFormat *udf_get_extendedattr(struct inode *inode, uint32_t type,
 		else
 			offset = le32_to_cpu(eahd->appAttrLocation);
 
-		while (offset < iinfo->i_lenEAttr) {
+		while (offset + sizeof(*gaf) < iinfo->i_lenEAttr) {
+			uint32_t attrLength;
+
 			gaf = (struct genericFormat *)&ea[offset];
+			attrLength = le32_to_cpu(gaf->attrLength);
+
+			/* Detect undersized elements and buffer overflows */
+			if ((attrLength < sizeof(*gaf)) ||
+			    (attrLength > (iinfo->i_lenEAttr - offset)))
+				break;
+
 			if (le32_to_cpu(gaf->attrType) == type &&
 					gaf->attrSubtype == subtype)
 				return gaf;
 			else
-				offset += le32_to_cpu(gaf->attrLength);
+				offset += attrLength;
 		}
 	}