[PATCH v2] udf: udftime: prevent overflow in udf_disk_stamp_to_time()

[Roman Smirnov]

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 <jack@xxxxxxx>
Signed-off-by: Roman Smirnov <r.smirnov@xxxxxx>
---
 fs/udf/udftime.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/fs/udf/udftime.c b/fs/udf/udftime.c
index 758163af39c2..3113785af3cf 100644
--- a/fs/udf/udftime.c
+++ b/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 {
+		desk->tv_nsec = 0;
+	}
 }
 
 void
-- 
2.34.1