[PATCH 4.19 043/109] ptp: improve max_adj check against unreasonable values

[Sasha Levin]

From: Jakub Kicinski <kuba@xxxxxxxxxx>

[ 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@xxxxxxxxxx>
Acked-by: Richard Cochran <richardcochran@xxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 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 863958f3bb57..89632cc9c28f 100644
--- a/drivers/ptp/ptp_clock.c
+++ b/drivers/ptp/ptp_clock.c
@@ -76,7 +76,7 @@ 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
@@ -93,7 +93,7 @@ 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);
 
@@ -148,7 +148,7 @@ static int ptp_clock_adjtime(struct posix_clock *pc, struct 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 40ea83fcfdd5..99c3f4ee938e 100644
--- a/include/linux/ptp_clock_kernel.h
+++ b/include/linux/ptp_clock_kernel.h
@@ -210,7 +210,7 @@ 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