Commit 7a25a0a9 authored Aug 25, 2021 by Lukas Hannen Committed by Greg Kroah-Hartman Sep 15, 2021

time: Handle negative seconds correctly in timespec64_to_ns()



commit 39ff83f2f6cc5cc1458dfcea9697f96338210beb upstream.

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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent ae968e27

include/linux/time64.h

+7 −2

Original line number	Diff line number	Diff line
		@@ -33,7 +33,9 @@ struct itimerspec64 {
		#define TIME64_MIN (-TIME64_MAX - 1)

		#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)

		/*
		* Limits for settimeofday():
		@@ -132,10 +134,13 @@ static inline bool timespec64_valid_settod(const struct timespec64 *ts)
		*/
		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;
		}