Re: [PATCH] driver core: fix driver_set_override() issue with empty strings

[Stephen Hemminger]

On Thu,  1 Sep 2022 18:37:34 +0200
Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:

> Python likes to send an empty string for some sysfs files, including the
> driver_override field.  When commit 23d99baf9d72 ("PCI: Use
> driver_set_override() instead of open-coding") moved the PCI core to use
> the driver core function instead of hand-rolling their own handler, this
> showed up as a regression from some userspace tools, like DPDK.
> 
> Fix this up by actually looking at the length of the string first
> instead of trusting that userspace got it correct.
> 
> Reported-by: Stephen Hemminger <stephen@xxxxxxxxxxxxxxxxxx>
> Fixes: 23d99baf9d72 ("PCI: Use driver_set_override() instead of open-coding")
> Cc: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx>
> Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
> Cc: "Rafael J. Wysocki" <rafael@xxxxxxxxxx>
> Cc: Andy Shevchenko <andy.shevchenko@xxxxxxxxx>
> Cc: stable <stable@xxxxxxxxxx>
> Tested-by: Huisong Li <lihuisong@xxxxxxxxxx>
> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> ---
>  drivers/base/driver.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/base/driver.c b/drivers/base/driver.c
> index 15a75afe6b84..676b6275d5b5 100644
> --- a/drivers/base/driver.c
> +++ b/drivers/base/driver.c
> @@ -63,6 +63,12 @@ int driver_set_override(struct device *dev, const char **override,
>  	if (len >= (PAGE_SIZE - 1))
>  		return -EINVAL;
>  
> +	/*
> +	 * Compute the real length of the string in case userspace sends us a
> +	 * bunch of \0 characters like python likes to do.
> +	 */
> +	len = strlen(s);
> +
>  	if (!len) {
>  		/* Empty string passed - clear override */
>  		device_lock(dev);

Thanks for addressing this.

Reviewed-by: Stephen Hemminger <stephen@xxxxxxxxxxxxxxxxxx>