Commit 475b92f9 authored by Jakub Kicinski's avatar Jakub Kicinski Committed by David S. Miller
Browse files

ptp: improve max_adj check against unreasonable values 



Scaled PPM conversion to PPB may (on 64bit systems) result
in a value larger than s32 can hold (freq/scaled_ppm is a long).
This means the kernel will not correctly reject unreasonably
high ->freq values (e.g. > 4294967295ppb, 281474976645 scaled PPM).

The conversion is equivalent to a division by ~66 (65.536),
so the value of ppb is always smaller than ppm, but not small
enough to assume narrowing the type from long -> s32 is okay.

Note that reasonable user space (e.g. ptp4l) will not use such
high values, anyway, 4289046510ppb ~= 4.3x, so the fix is
somewhat pedantic.

Fixes: d39a7435 ("ptp: validate the requested frequency adjustment.")
Fixes: d94ba80e ("ptp: Added a brand new class driver for ptp clocks.")
Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
Acked-by: default avatarRichard Cochran <richardcochran@gmail.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 2214fb53

drivers/ptp/ptp_clock.c

+3 −3
Original line number Diff line number Diff line
@@ -63,7 +63,7 @@ static void enqueue_external_timestamp(struct timestamp_event_queue *queue, 
	spin_unlock_irqrestore(&queue->lock, flags);

}



s32 scaled_ppm_to_ppb(long ppm)

long scaled_ppm_to_ppb(long ppm)

{

	/*

	 * The 'freq' field in the 'struct timex' is in parts per
@@ -80,7 +80,7 @@ s32 scaled_ppm_to_ppb(long ppm) 
	s64 ppb = 1 + ppm;

	ppb *= 125;

	ppb >>= 13;

	return (s32) ppb;

	return (long) ppb;

}

EXPORT_SYMBOL(scaled_ppm_to_ppb);
@@ -138,7 +138,7 @@ static int ptp_clock_adjtime(struct posix_clock *pc, struct __kernel_timex *tx) 
		delta = ktime_to_ns(kt);

		err = ops->adjtime(ops, delta);

	} else if (tx->modes & ADJ_FREQUENCY) {

		s32 ppb = scaled_ppm_to_ppb(tx->freq);

		long ppb = scaled_ppm_to_ppb(tx->freq);

		if (ppb > ops->max_adj || ppb < -ops->max_adj)

			return -ERANGE;

		if (ops->adjfine)

include/linux/ptp_clock_kernel.h

+1 −1
Original line number Diff line number Diff line
@@ -235,7 +235,7 @@ extern int ptp_clock_index(struct ptp_clock *ptp); 
 * @ppm:    Parts per million, but with a 16 bit binary fractional field

 */



extern s32 scaled_ppm_to_ppb(long ppm);

extern long scaled_ppm_to_ppb(long ppm);



/**

 * ptp_find_pin() - obtain the pin index of a given auxiliary function