linux-hardening - [PATCH v3 105/108] pwm: Ensure a struct pwm has the same lifetime as its pwm

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Message-ID: <20231121134901.208535-106-u.kleine-koenig@pengutronix.de>
Date: Tue, 21 Nov 2023 14:50:47 +0100
From: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To: Thierry Reding <thierry.reding@...il.com>,
	Kees Cook <keescook@...omium.org>
Cc: "Gustavo A. R. Silva" <gustavoars@...nel.org>,
	linux-pwm@...r.kernel.org,
	kernel@...gutronix.de,
	linux-hardening@...r.kernel.org
Subject: [PATCH v3 105/108] pwm: Ensure a struct pwm has the same lifetime as its pwm_chip

It's required to not free the memory underlying a requested PWM
while a consumer still has a reference to it. While currently a pwm_chip
doesn't life long enough in all cases, linking the struct pwm to the
pwm_chip results in the right lifetime as soon as the pwmchip is living
long enough. This happens with the following commits.

Note this is a breaking change for all pwm drivers that don't use
pwmchip_alloc().

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
---
 drivers/pwm/core.c  | 26 ++++++++++----------------
 include/linux/pwm.h |  2 +-
 2 files changed, 11 insertions(+), 17 deletions(-)

diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c
index 15942210aa08..029aa1c69591 100644
--- a/drivers/pwm/core.c
+++ b/drivers/pwm/core.c
@@ -198,7 +198,7 @@ static bool pwm_ops_check(const struct pwm_chip *chip)
 
 void *pwmchip_priv(struct pwm_chip *chip)
 {
-	return (void *)chip + sizeof(*chip);
+	return (void *)chip + struct_size(chip, pwms, chip->npwm);
 }
 EXPORT_SYMBOL_GPL(pwmchip_priv);
 
@@ -206,8 +206,9 @@ struct pwm_chip *devm_pwmchip_alloc(struct device *parent, unsigned int npwm, si
 {
 	struct pwm_chip *chip;
 	size_t alloc_size;
+	unsigned int i;
 
-	alloc_size = size_add(sizeof(*chip), sizeof_priv);
+	alloc_size = size_add(struct_size(chip, pwms, npwm), sizeof_priv);
 
 	chip = devm_kzalloc(parent, alloc_size, GFP_KERNEL);
 	if (!chip)
@@ -217,6 +218,13 @@ struct pwm_chip *devm_pwmchip_alloc(struct device *parent, unsigned int npwm, si
 	chip->npwm = npwm;
 	chip->uses_pwmchip_alloc = true;
 
+	for (i = 0; i < chip->npwm; i++) {
+		struct pwm_device *pwm = &chip->pwms[i];
+
+		pwm->chip = chip;
+		pwm->hwpwm = i;
+	}
+
 	return chip;
 }
 EXPORT_SYMBOL_GPL(devm_pwmchip_alloc);
@@ -234,7 +242,6 @@ EXPORT_SYMBOL_GPL(devm_pwmchip_alloc);
 int __pwmchip_add(struct pwm_chip *chip, struct module *owner)
 {
 	int ret;
-	unsigned i;
 
 	if (!chip || !chip->dev || !chip->ops || !chip->npwm)
 		return -EINVAL;
@@ -253,26 +260,15 @@ int __pwmchip_add(struct pwm_chip *chip, struct module *owner)
 
 	chip->owner = owner;
 
-	chip->pwms = kcalloc(chip->npwm, sizeof(*chip->pwms), GFP_KERNEL);
-	if (!chip->pwms)
-		return -ENOMEM;
-
 	mutex_lock(&pwm_lock);
 
 	ret = idr_alloc(&pwmchip_idr, chip, 0, 0, GFP_KERNEL);
 	if (ret < 0) {
 		mutex_unlock(&pwm_lock);
-		kfree(chip->pwms);
 		return ret;
 	}
 
 	chip->id = ret;
-	for (i = 0; i < chip->npwm; i++) {
-		struct pwm_device *pwm = &chip->pwms[i];
-
-		pwm->chip = chip;
-		pwm->hwpwm = i;
-	}
 
 	mutex_unlock(&pwm_lock);
 
@@ -303,8 +299,6 @@ void pwmchip_remove(struct pwm_chip *chip)
 	idr_remove(&pwmchip_idr, chip->id);
 
 	mutex_unlock(&pwm_lock);
-
-	kfree(chip->pwms);
 }
 EXPORT_SYMBOL_GPL(pwmchip_remove);
 
diff --git a/include/linux/pwm.h b/include/linux/pwm.h
index b8e70ee01d31..a7294ef1495d 100644
--- a/include/linux/pwm.h
+++ b/include/linux/pwm.h
@@ -302,7 +302,7 @@ struct pwm_chip {
 
 	/* only used internally by the PWM framework */
 	bool uses_pwmchip_alloc;
-	struct pwm_device *pwms;
+	struct pwm_device pwms[] __counted_by(npwm);
 };
 
 static inline struct device *pwmchip_parent(struct pwm_chip *chip)
-- 
2.42.0