linux-kernel - [PATCH v3 2/3] clocksource/drivers/arm_global

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Date: Sun, 25 Feb 2024 16:13:35 +0100
From: Martin Blumenstingl <martin.blumenstingl@...glemail.com>
To: daniel.lezcano@...aro.org,
	tglx@...utronix.de
Cc: linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	patrice.chotard@...s.st.com,
	linux-amlogic@...ts.infradead.org,
	Martin Blumenstingl <martin.blumenstingl@...glemail.com>
Subject: [PATCH v3 2/3] clocksource/drivers/arm_global_timer: Guard against division by zero

The result of the division of new_rate by gt_target_rate can be zero (if
new_rate is smaller than gt_target_rate). Using that result as divisor
without checking can result in a division by zero error. Guard against
this by checking for a zero value earlier.
While here, also change the psv variable to an unsigned long to make
sure we don't overflow the datatype as all other types involved are also
unsiged long.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@...glemail.com>
---
 drivers/clocksource/arm_global_timer.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/drivers/clocksource/arm_global_timer.c b/drivers/clocksource/arm_global_timer.c
index fb3ffd54c822..257599d682f0 100644
--- a/drivers/clocksource/arm_global_timer.c
+++ b/drivers/clocksource/arm_global_timer.c
@@ -291,18 +291,17 @@ static int gt_clk_rate_change_cb(struct notifier_block *nb,
 	switch (event) {
 	case PRE_RATE_CHANGE:
 	{
-		int psv;
+		unsigned long psv;
 
-		psv = DIV_ROUND_CLOSEST(ndata->new_rate,
-					gt_target_rate);
-
-		if (abs(gt_target_rate - (ndata->new_rate / psv)) > MAX_F_ERR)
+		psv = DIV_ROUND_CLOSEST(ndata->new_rate, gt_target_rate);
+		if (!psv ||
+		    abs(gt_target_rate - (ndata->new_rate / psv)) > MAX_F_ERR)
 			return NOTIFY_BAD;
 
 		psv--;
 
 		/* prescaler within legal range? */
-		if (psv < 0 || psv > GT_CONTROL_PRESCALER_MAX)
+		if (psv > GT_CONTROL_PRESCALER_MAX)
 			return NOTIFY_BAD;
 
 		/*
-- 
2.44.0