From 39ff83f2f6cc5cc1458dfcea9697f96338210beb Mon Sep 17 00:00:00 2001

From: Lukas Hannen <lukas.hannen@opensource.tttech-industrial.com>

Date: Wed, 25 Aug 2021 10:12:43 +0000

Subject: [PATCH] time: Handle negative seconds correctly in timespec64_to_ns()

Git-commit: 39ff83f2f6cc5cc1458dfcea9697f96338210beb

References: git-fixes

Patch-mainline: v5.15-rc1

timespec64_ns() prevents multiplication overflows by comparing the seconds

value of the timespec to KTIME_SEC_MAX. If the value is greater or equal it

returns KTIME_MAX.

But that check casts the signed seconds value to unsigned which makes the

comparision true for all negative values and therefore return wrongly

KTIME_MAX.

Negative second values are perfectly valid and required in some places,

e.g. ptp_clock_adjtime().

Remove the cast and add a check for the negative boundary which is required

to prevent undefined behaviour due to multiplication underflow.

Fixes: cb47755725da ("time: Prevent undefined behaviour in timespec64_to_ns()")'

Signed-off-by: Lukas Hannen <lukas.hannen@opensource.tttech-industrial.com>

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

Cc: stable@vger.kernel.org

Link: https://lore.kernel.org/r/AM6PR01MB541637BD6F336B8FFB72AF80EEC69@AM6PR01MB5416.eurprd01.prod.exchangelabs.com

Signed-off-by: Oliver Neukum <oneukum@suse.com>

---

 include/linux/time64.h |    9 +++++++--

 1 file changed, 7 insertions(+), 2 deletions(-)

--- a/include/linux/time64.h

+++ b/include/linux/time64.h

@@ -39,7 +39,9 @@ struct itimerspec64 {

 /* Located here for timespec[64]_valid_strict */

 #define TIME64_MAX			((s64)~((u64)1 << 63))

 #define KTIME_MAX			((s64)~((u64)1 << 63))

+#define KTIME_MIN			(-KTIME_MAX - 1)

 #define KTIME_SEC_MAX			(KTIME_MAX / NSEC_PER_SEC)

+#define KTIME_SEC_MIN			(KTIME_MIN / NSEC_PER_SEC)

 #if __BITS_PER_LONG == 64

@@ -188,10 +190,13 @@ static inline bool timespec64_valid_stri

  */

 static inline s64 timespec64_to_ns(const struct timespec64 *ts)

 {

-	/* Prevent multiplication overflow */

-	if ((unsigned long long)ts->tv_sec >= KTIME_SEC_MAX)

+	/* Prevent multiplication overflow / underflow */

+	if (ts->tv_sec >= KTIME_SEC_MAX)

 		return KTIME_MAX;

+	if (ts->tv_sec <= KTIME_SEC_MIN)

+		return KTIME_MIN;

+

 	return ((s64) ts->tv_sec * NSEC_PER_SEC) + ts->tv_nsec;

 }