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Commit 063444d6 authored by Krzysztof Kozlowski's avatar Krzysztof Kozlowski Committed by Greg Kroah-Hartman
Browse files

driver: platform: Add helper for safer setting of driver_override 



commit 6c2f421174273de8f83cde4286d1c076d43a2d35 upstream.

Several core drivers and buses expect that driver_override is a
dynamically allocated memory thus later they can kfree() it.

However such assumption is not documented, there were in the past and
there are already users setting it to a string literal. This leads to
kfree() of static memory during device release (e.g. in error paths or
during unbind):

    kernel BUG at ../mm/slub.c:3960!
    Internal error: Oops - BUG: 0 [#1] PREEMPT SMP ARM
    ...
    (kfree) from [<c058da50>] (platform_device_release+0x88/0xb4)
    (platform_device_release) from [<c0585be0>] (device_release+0x2c/0x90)
    (device_release) from [<c0a69050>] (kobject_put+0xec/0x20c)
    (kobject_put) from [<c0f2f120>] (exynos5_clk_probe+0x154/0x18c)
    (exynos5_clk_probe) from [<c058de70>] (platform_drv_probe+0x6c/0xa4)
    (platform_drv_probe) from [<c058b7ac>] (really_probe+0x280/0x414)
    (really_probe) from [<c058baf4>] (driver_probe_device+0x78/0x1c4)
    (driver_probe_device) from [<c0589854>] (bus_for_each_drv+0x74/0xb8)
    (bus_for_each_drv) from [<c058b48c>] (__device_attach+0xd4/0x16c)
    (__device_attach) from [<c058a638>] (bus_probe_device+0x88/0x90)
    (bus_probe_device) from [<c05871fc>] (device_add+0x3dc/0x62c)
    (device_add) from [<c075ff10>] (of_platform_device_create_pdata+0x94/0xbc)
    (of_platform_device_create_pdata) from [<c07600ec>] (of_platform_bus_create+0x1a8/0x4fc)
    (of_platform_bus_create) from [<c0760150>] (of_platform_bus_create+0x20c/0x4fc)
    (of_platform_bus_create) from [<c07605f0>] (of_platform_populate+0x84/0x118)
    (of_platform_populate) from [<c0f3c964>] (of_platform_default_populate_init+0xa0/0xb8)
    (of_platform_default_populate_init) from [<c01031f8>] (do_one_initcall+0x8c/0x404)

Provide a helper which clearly documents the usage of driver_override.
This will allow later to reuse the helper and reduce the amount of
duplicated code.

Convert the platform driver to use a new helper and make the
driver_override field const char (it is not modified by the core).

Reviewed-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: default avatarKrzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20220419113435.246203-2-krzysztof.kozlowski@linaro.org


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: default avatarLee Jones <lee@kernel.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 83ecffd4

drivers/base/driver.c

+69 −0
Original line number Diff line number Diff line
@@ -29,6 +29,75 @@ static struct device *next_device(struct klist_iter *i) 
	return dev;

}



/**

 * driver_set_override() - Helper to set or clear driver override.

 * @dev: Device to change

 * @override: Address of string to change (e.g. &device->driver_override);

 *            The contents will be freed and hold newly allocated override.

 * @s: NUL-terminated string, new driver name to force a match, pass empty

 *     string to clear it ("" or "\n", where the latter is only for sysfs

 *     interface).

 * @len: length of @s

 *

 * Helper to set or clear driver override in a device, intended for the cases

 * when the driver_override field is allocated by driver/bus code.

 *

 * Returns: 0 on success or a negative error code on failure.

 */

int driver_set_override(struct device *dev, const char **override,

			const char *s, size_t len)

{

	const char *new, *old;

	char *cp;



	if (!override || !s)

		return -EINVAL;



	/*

	 * The stored value will be used in sysfs show callback (sysfs_emit()),

	 * which has a length limit of PAGE_SIZE and adds a trailing newline.

	 * Thus we can store one character less to avoid truncation during sysfs

	 * show.

	 */

	if (len >= (PAGE_SIZE - 1))

		return -EINVAL;



	if (!len) {

		/* Empty string passed - clear override */

		device_lock(dev);

		old = *override;

		*override = NULL;

		device_unlock(dev);

		kfree(old);



		return 0;

	}



	cp = strnchr(s, len, '\n');

	if (cp)

		len = cp - s;



	new = kstrndup(s, len, GFP_KERNEL);

	if (!new)

		return -ENOMEM;



	device_lock(dev);

	old = *override;

	if (cp != s) {

		*override = new;

	} else {

		/* "\n" passed - clear override */

		kfree(new);

		*override = NULL;

	}

	device_unlock(dev);



	kfree(old);



	return 0;

}

EXPORT_SYMBOL_GPL(driver_set_override);



/**

 * driver_for_each_device - Iterator for devices bound to a driver.

 * @drv: Driver we're iterating.

drivers/base/platform.c

+4 −24
Original line number Diff line number Diff line
@@ -973,31 +973,11 @@ static ssize_t driver_override_store(struct device *dev, 
				     const char *buf, size_t count)

{

	struct platform_device *pdev = to_platform_device(dev);

	char *driver_override, *old, *cp;



	/* We need to keep extra room for a newline */

	if (count >= (PAGE_SIZE - 1))

		return -EINVAL;



	driver_override = kstrndup(buf, count, GFP_KERNEL);

	if (!driver_override)

		return -ENOMEM;



	cp = strchr(driver_override, '\n');

	if (cp)

		*cp = '\0';



	device_lock(dev);

	old = pdev->driver_override;

	if (strlen(driver_override)) {

		pdev->driver_override = driver_override;

	} else {

		kfree(driver_override);

		pdev->driver_override = NULL;

	}

	device_unlock(dev);

	int ret;



	kfree(old);

	ret = driver_set_override(dev, &pdev->driver_override, buf, count);

	if (ret)

		return ret;



	return count;

}

include/linux/device.h

+2 −0
Original line number Diff line number Diff line
@@ -422,6 +422,8 @@ extern int __must_check driver_create_file(struct device_driver *driver, 
extern void driver_remove_file(struct device_driver *driver,

			       const struct driver_attribute *attr);



int driver_set_override(struct device *dev, const char **override,

			const char *s, size_t len);

extern int __must_check driver_for_each_device(struct device_driver *drv,

					       struct device *start,

					       void *data,

include/linux/platform_device.h

+5 −1
Original line number Diff line number Diff line
@@ -29,7 +29,11 @@ struct platform_device { 
	struct resource	*resource;



	const struct platform_device_id	*id_entry;

	char *driver_override; /* Driver name to force a match */

	/*

	 * Driver name to force a match.  Do not set directly, because core

	 * frees it.  Use driver_set_override() to set or clear it.

	 */

	const char *driver_override;



	/* MFD cell pointer */

	struct mfd_cell *mfd_cell;