udf: udftime: prevent overflow in udf_disk_stamp_to_time()

An overflow can occur in a situation where src.centiseconds
takes the value of 255. This situation is unlikely, but there
is no validation check anywere in the code.

Found by Linux Verification Center (linuxtesting.org) with Svace.

Suggested-by: Jan Kara <[email protected]>
Signed-off-by: Roman Smirnov <[email protected]>
Reviewed-by: Sergey Shtylyov <[email protected]>
Signed-off-by: Jan Kara <[email protected]>
Message-Id: <[email protected]>

Author: RSmirnov512

fs/udf/udftime.c

@@ -46,13 +46,18 @@ udf_disk_stamp_to_time(struct timespec64 *dest, struct timestamp src)
 	dest->tv_sec = mktime64(year, src.month, src.day, src.hour, src.minute,
 			src.second);
 	dest->tv_sec -= offset * 60;
-	dest->tv_nsec = 1000 * (src.centiseconds * 10000 +
-			src.hundredsOfMicroseconds * 100 + src.microseconds);
+
 	/*
 	 * Sanitize nanosecond field since reportedly some filesystems are
 	 * recorded with bogus sub-second values.
 	 */
-	dest->tv_nsec %= NSEC_PER_SEC;
+	if (src.centiseconds < 100 && src.hundredsOfMicroseconds < 100 &&
+	    src.microseconds < 100) {
+		dest->tv_nsec = 1000 * (src.centiseconds * 10000 +
+			src.hundredsOfMicroseconds * 100 + src.microseconds);
+	} else {
+		dest->tv_nsec = 0;
+	}
 }
 
 void