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ptp: improve max_adj check against unreasonable values

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[ Upstream commit 475b92f932168a78da8109acd10bfb7578b8f2bb ]

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: d39a743511 ("ptp: validate the requested frequency adjustment.")
Fixes: d94ba80ebb ("ptp: Added a brand new class driver for ptp clocks.")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Jakub Kicinski 2021-06-14 15:24:05 -07:00 committed by Greg Kroah-Hartman
parent 5fc6ed1831
commit 9a47949562
2 changed files with 4 additions and 4 deletions
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6
drivers/ptp/ptp_clock.c
View File

@ -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)

2
include/linux/ptp_clock_kernel.h
View File

@ -222,7 +222,7 @@ 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