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time: Handle negative seconds correctly in timespec64_to_ns()

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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: cb47755725 ("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>
This commit is contained in:
Lukas Hannen 2021-08-25 10:12:43 +00:00 committed by AuxXxilium
parent 9cedd55c11
commit d545fd4f97
1 changed files with 7 additions and 2 deletions
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9
include/linux/time64.h
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@ -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;
}