linux-kernel - [PATCH AUTOSEL 6.2 08/20] pwm: Zero-initialize the pwm_state passed to driver's .get

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Message-Id: <20230413023601.74410-8-sashal@kernel.org>
Date:   Wed, 12 Apr 2023 22:35:46 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Munehisa Kamata <kamatam@...zon.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Sasha Levin <sashal@...nel.org>, linux-pwm@...r.kernel.org
Subject: [PATCH AUTOSEL 6.2 08/20] pwm: Zero-initialize the pwm_state passed to driver's .get_state()

From: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>

[ Upstream commit 1271a7b98e7989ba6bb978e14403fc84efe16e13 ]

This is just to ensure that .usage_power is properly initialized and
doesn't contain random stack data. The other members of struct pwm_state
should get a value assigned in a successful call to .get_state(). So in
the absence of bugs in driver implementations, this is only a safe-guard
and no fix.

Reported-by: Munehisa Kamata <kamatam@...zon.com>
Link: https://lore.kernel.org/r/20230310214004.2619480-1-u.kleine-koenig@pengutronix.de
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
Signed-off-by: Thierry Reding <thierry.reding@...il.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/pwm/core.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c
index e01147f66e15a..474725714a05b 100644
--- a/drivers/pwm/core.c
+++ b/drivers/pwm/core.c
@@ -115,7 +115,14 @@ static int pwm_device_request(struct pwm_device *pwm, const char *label)
 	}
 
 	if (pwm->chip->ops->get_state) {
-		struct pwm_state state;
+		/*
+		 * Zero-initialize state because most drivers are unaware of
+		 * .usage_power. The other members of state are supposed to be
+		 * set by lowlevel drivers. We still initialize the whole
+		 * structure for simplicity even though this might paper over
+		 * faulty implementations of .get_state().
+		 */
+		struct pwm_state state = { 0, };
 
 		err = pwm->chip->ops->get_state(pwm->chip, pwm, &state);
 		trace_pwm_get(pwm, &state, err);
@@ -448,7 +455,7 @@ static void pwm_apply_state_debug(struct pwm_device *pwm,
 {
 	struct pwm_state *last = &pwm->last;
 	struct pwm_chip *chip = pwm->chip;
-	struct pwm_state s1, s2;
+	struct pwm_state s1 = { 0 }, s2 = { 0 };
 	int err;
 
 	if (!IS_ENABLED(CONFIG_PWM_DEBUG))
@@ -530,6 +537,7 @@ static void pwm_apply_state_debug(struct pwm_device *pwm,
 		return;
 	}
 
+	*last = (struct pwm_state){ 0 };
 	err = chip->ops->get_state(chip, pwm, last);
 	trace_pwm_get(pwm, last, err);
 	if (err)
-- 
2.39.2