Re: [PATCH v7 01/12] driver: platform: Add helper for safer setting of driver_override

On Tue, Apr 19, 2022 at 1:34 PM Krzysztof Kozlowski krzysztof.kozlowski@linaro.org wrote:

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).

Signed-off-by: Krzysztof Kozlowski krzysztof.kozlowski@linaro.org

drivers/base/driver.c | 69 +++++++++++++++++++++++++++++++++ drivers/base/platform.c | 28 ++----------- include/linux/device/driver.h | 2 + include/linux/platform_device.h | 6 ++- 4 files changed, 80 insertions(+), 25 deletions(-)

diff --git a/drivers/base/driver.c b/drivers/base/driver.c index 8c0d33e182fd..1b9d47b10bd0 100644 --- a/drivers/base/driver.c +++ b/drivers/base/driver.c @@ -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.
    

I would stick to one-line description here and possibly expand them in the body of the comment.

Regardless, I think that the series is an improvement, so please feel free to add

Reviewed-by: Rafael J. Wysocki rafael.j.wysocki@intel.com

to this patch and

Acked-by: Rafael J. Wysocki rafael.j.wysocki@intel.com

to the other patches in the series.

• • @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.

diff --git a/drivers/base/platform.c b/drivers/base/platform.c index 8cc272fd5c99..b684157b7f2f 100644 --- a/drivers/base/platform.c +++ b/drivers/base/platform.c @@ -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;
  

} diff --git a/include/linux/device/driver.h b/include/linux/device/driver.h index 15e7c5e15d62..700453017e1c 100644 --- a/include/linux/device/driver.h +++ b/include/linux/device/driver.h @@ -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, diff --git a/include/linux/platform_device.h b/include/linux/platform_device.h index 7c96f169d274..582d83ed9a91 100644 --- a/include/linux/platform_device.h +++ b/include/linux/platform_device.h @@ -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;
  

-- 2.32.0