Committer: Thomas Gleixner tglx@linutronix.de CommitterDate: Wed, 08 Sep 2021 17:44:26 +02:00

time: Handle negative seconds correctly in timespec64_to_ns()

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@AM6PR01MB54... abs.com

---

include/linux/time64.h | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/include/linux/time64.h b/include/linux/time64.h index 5117cb5..81b9686 100644 --- a/include/linux/time64.h +++ b/include/linux/time64.h @@ -25,7 +25,9 @@ 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():

@@ -124,10 +126,13 @@ 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;

}

Adding tv_nsec can still overflow - even if tv_nsec is bounded to +/- 1 second. This is no more 'garbage in' => 'garbage out' than the code without the multiply under/overflow check.

David

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