Re: [PATCH net v2 2/3] net: core: add netdev_class_has_file_ns() helper function

[Greg KH <gregkh@linuxfoundation.org>]

On Sat, Apr 04, 2020 at 02:19:09PM +0000, Taehee Yoo wrote:
> This helper function is to check whether the class file "/sys/class/net/*"
> is existing or not.
> In the next patch, this helper function will be used.
> 
> Reported-by: syzbot+830c6dbfc71edc4f0b8f@syzkaller.appspotmail.com
> Fixes: b76cdba9cdb2 ("[PATCH] bonding: add sysfs functionality to bonding (large)")
> Signed-off-by: Taehee Yoo <ap420073@gmail.com>
> ---
> 
> v1 -> v2:
>  - use class_has_file_ns(), which is introduced by the first patch.
> 
>  include/linux/netdevice.h | 2 +-
>  net/core/net-sysfs.c      | 6 ++++++
>  2 files changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index 130a668049ab..a04c487c0975 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -4555,7 +4555,7 @@ int netdev_class_create_file_ns(const struct class_attribute *class_attr,
>  				const void *ns);
>  void netdev_class_remove_file_ns(const struct class_attribute *class_attr,
>  				 const void *ns);
> -
> +bool netdev_class_has_file_ns(const char *name, const void *ns);
>  static inline int netdev_class_create_file(const struct class_attribute *class_attr)
>  {
>  	return netdev_class_create_file_ns(class_attr, NULL);
> diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
> index cf0215734ceb..8a20d658eff0 100644
> --- a/net/core/net-sysfs.c
> +++ b/net/core/net-sysfs.c
> @@ -1914,6 +1914,12 @@ void netdev_class_remove_file_ns(const struct class_attribute *class_attr,
>  }
>  EXPORT_SYMBOL(netdev_class_remove_file_ns);
>  
> +bool netdev_class_has_file_ns(const char *name, const void *ns)
> +{
> +	return class_has_file_ns(&net_class, name, ns);
> +}
> +EXPORT_SYMBOL(netdev_class_has_file_ns);

Again, this feels broken, it can not solve a race condition.

greg k-h