[PATCH 5.12 064/178] ptp: improve max_adj check against unreasonable values

Greg Kroah-Hartman
2021-06-21T16:45:44Z

From: Jakub Kicinski <kuba@kernel.org>

[ 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: d39a743511cd ("ptp: validate the requested frequency adjustment.")
Fixes: d94ba80ebbea ("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>
---
drivers/ptp/ptp_clock.c | 6 +++---
include/linux/ptp_clock_kernel.h | 2 +-
2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/ptp/ptp_clock.c b/drivers/ptp/ptp_clock.c
index 03a246e60fd9..21c4c34c52d8 100644
--- a/drivers/ptp/ptp_clock.c
+++ b/drivers/ptp/ptp_clock.c
@@ -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)
diff --git a/include/linux/ptp_clock_kernel.h b/include/linux/ptp_clock_kernel.h
index 0d47fd33b228..51d7f1b8b32a 100644
--- a/include/linux/ptp_clock_kernel.h
+++ b/include/linux/ptp_clock_kernel.h
@@ -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
--
2.30.2