Commit 6c2f4211 authored by Krzysztof Kozlowski's avatar Krzysztof Kozlowski Committed by Greg Kroah-Hartman

driver: platform: Add helper for safer setting of driver_override

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.orgSigned-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent bc67cac1
......@@ -30,6 +30,75 @@ 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.
......
......@@ -1275,31 +1275,11 @@ 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;
}
......
......@@ -151,6 +151,8 @@ 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,
......
......@@ -31,7 +31,11 @@ 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;
......
Markdown is supported
0%
or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment