[PATCH] 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. It is necessary
to convert the type of expression to 64-bit.

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

Suggested-by: Sergey Shtylyov <s.shtylyov@xxxxxx>
Signed-off-by: Roman Smirnov <r.smirnov@xxxxxx>
Reviewed-by: Sergey Shtylyov <s.shtylyov@xxxxxx>
---
 fs/udf/udftime.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/udf/udftime.c b/fs/udf/udftime.c
index 758163af39c2..2824b90c8288 100644
--- a/fs/udf/udftime.c
+++ b/fs/udf/udftime.c
@@ -33,6 +33,7 @@ udf_disk_stamp_to_time(struct timespec64 *dest, struct timestamp src)
 	u16 year = le16_to_cpu(src.year);
 	uint8_t type = typeAndTimezone >> 12;
 	int16_t offset;
+	int64_t nsec;
 
 	if (type == 1) {
 		offset = typeAndTimezone << 4;
@@ -46,13 +47,13 @@ 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 +
+	nsec = 1000LL * (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;
+	dest->tv_nsec = do_div(nsec, NSEC_PER_SEC);
 }
 
 void
-- 
2.34.1