[PATCH] ptp: Limit time setting of PTP clocks

[PATCH] ptp: Limit time setting of PTP clocks

[Miroslav Lichvar]

Networking drivers implementing PTP clocks and kernel socket code
handling hardware timestamps use the 64-bit signed ktime_t type counting
nanoseconds. When a PTP clock reaches the maximum value in year 2262,
the timestamps returned to applications will overflow into year 1667.
The same thing happens when injecting a large offset with
clock_adjtime(ADJ_SETOFFSET).

The commit 7a8e61f84786 ("timekeeping: Force upper bound for setting
CLOCK_REALTIME") limited the maximum accepted value setting the system
clock to 30 years before the maximum representable value (i.e. year
2232) to avoid the overflow, assuming the system will not run for more
than 30 years.

Enforce the same limit for PTP clocks. Don't allow negative values and
values closer than 30 years to the maximum value. Drivers may implement
an even lower limit if the hardware registers cannot represent the whole
interval between years 1970 and 2262 in the required resolution.

Signed-off-by: Miroslav Lichvar <mlichvar@redhat.com>
Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: John Stultz <jstultz@google.com>
Cc: Arnd Bergmann <arnd@arndb.de>
---
 drivers/ptp/ptp_clock.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/drivers/ptp/ptp_clock.c b/drivers/ptp/ptp_clock.c
index c56cd0f63909..bd7c5f534be6 100644
--- a/drivers/ptp/ptp_clock.c
+++ b/drivers/ptp/ptp_clock.c
@@ -100,6 +100,9 @@ static int ptp_clock_settime(struct posix_clock *pc, const struct timespec64 *tp
 		return -EBUSY;
 	}
 
+	if (!timespec64_valid_settod(tp))
+		return -EINVAL;
+
 	return  ptp->info->settime64(ptp->info, tp);
 }
 
@@ -129,7 +132,7 @@ static int ptp_clock_adjtime(struct posix_clock *pc, struct __kernel_timex *tx)
 	ops = ptp->info;
 
 	if (tx->modes & ADJ_SETOFFSET) {
-		struct timespec64 ts;
+		struct timespec64 ts, ts2;
 		ktime_t kt;
 		s64 delta;
 
@@ -139,7 +142,14 @@ static int ptp_clock_adjtime(struct posix_clock *pc, struct __kernel_timex *tx)
 		if (!(tx->modes & ADJ_NANO))
 			ts.tv_nsec *= 1000;
 
-		if ((unsigned long) ts.tv_nsec >= NSEC_PER_SEC)
+		/* Make sure the offset is valid */
+		err = ptp_clock_gettime(pc, &ts2);
+		if (err)
+			return err;
+		ts2 = timespec64_add(ts2, ts);
+
+		if ((unsigned long) ts.tv_nsec >= NSEC_PER_SEC ||
+		    !timespec64_valid_settod(&ts2))
 			return -EINVAL;
 
 		kt = timespec64_to_ktime(ts);
-- 
2.46.0

Re: [PATCH] ptp: Limit time setting of PTP clocks

[Richard Cochran]

> diff --git a/drivers/ptp/ptp_clock.c b/drivers/ptp/ptp_clock.c
> index c56cd0f63909..bd7c5f534be6 100644
> --- a/drivers/ptp/ptp_clock.c
> +++ b/drivers/ptp/ptp_clock.c
> @@ -100,6 +100,9 @@ static int ptp_clock_settime(struct posix_clock *pc, const struct timespec64 *tp
>  		return -EBUSY;
>  	}
>  
> +	if (!timespec64_valid_settod(tp))
> +		return -EINVAL;

Why not perform the test earlier, in SYSCALL_DEFINE2(clock_settime, ...) ?

Thanks,
Richard

Re: [PATCH] ptp: Limit time setting of PTP clocks

[Miroslav Lichvar]

On Mon, Sep 09, 2024 at 08:48:24AM -0700, Richard Cochran wrote:
> > diff --git a/drivers/ptp/ptp_clock.c b/drivers/ptp/ptp_clock.c
> > index c56cd0f63909..bd7c5f534be6 100644
> > --- a/drivers/ptp/ptp_clock.c
> > +++ b/drivers/ptp/ptp_clock.c
> > @@ -100,6 +100,9 @@ static int ptp_clock_settime(struct posix_clock *pc, const struct timespec64 *tp
> >  		return -EBUSY;
> >  	}
> >  
> > +	if (!timespec64_valid_settod(tp))
> > +		return -EINVAL;
> 
> Why not perform the test earlier, in SYSCALL_DEFINE2(clock_settime, ...) ?

It would be more code as there are also the 32-bit compat variants of
the functions. The adjtime function would probably need to handle
missing gettime.

The limit would apply to all clocks, not just PTP clocks. If nothing
else, I suspect it would change returned errors for other clocks
trying to set the an unacceptable timespec value.

-- 
Miroslav Lichvar