Re: [PATCH RESEND net 1/3] class: add class_find_and_get_file_ns() helper function

[Greg KH]

On Tue, Mar 24, 2020 at 02:17:22PM +0000, Taehee Yoo wrote:
> The new helper function is to find and get a class file.
> This function is useful for checking whether the class file is existing
> or not. This function will be used by networking stack to
> check "/sys/class/net/*" file.
> 
> Reported-by: syzbot+830c6dbfc71edc4f0b8f@xxxxxxxxxxxxxxxxxxxxxxxxx
> Fixes: b76cdba9cdb2 ("[PATCH] bonding: add sysfs functionality to bonding (large)")
> Signed-off-by: Taehee Yoo <ap420073@xxxxxxxxx>
> ---
>  drivers/base/class.c         | 12 ++++++++++++
>  include/linux/device/class.h |  4 +++-
>  2 files changed, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/base/class.c b/drivers/base/class.c
> index bcd410e6d70a..dedf41f32f0d 100644
> --- a/drivers/base/class.c
> +++ b/drivers/base/class.c
> @@ -105,6 +105,17 @@ void class_remove_file_ns(struct class *cls, const struct class_attribute *attr,
>  		sysfs_remove_file_ns(&cls->p->subsys.kobj, &attr->attr, ns);
>  }
>  
> +struct kernfs_node *class_find_and_get_file_ns(struct class *cls,
> +					       const char *name,
> +					       const void *ns)
> +{
> +	struct kernfs_node *kn = NULL;
> +
> +	if (cls)
> +		kn = kernfs_find_and_get_ns(cls->p->subsys.kobj.sd, name, ns);
> +	return kn;
> +}
> +

You can put the EXPORT_SYMBOL_GPL() under here.

And can you document what this function actually is in some kerneldoc?

But, returning a kernfs_node from a driver core is _REALLY_ odd.  Why do
you need this and who cares about kernfs here?

thanks,

greg k-h