linux-kernel - Re: [PATCH] fs: sysfs: do not remove files if group is null

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Date:   Sat, 21 Aug 2021 13:52:44 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Daniel Steger <daniel.steger@...inx.com>
Cc:     rafael@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fs: sysfs: do not remove files if group is null

On Thu, Aug 19, 2021 at 12:10:20PM -0700, Daniel Steger wrote:
> The current implementation allows the remove_files() API to be
> called without checking if the grp->name is null. Ensure that
> the group name is valid prior to removing files.
> 
> This patch fixes a race condition where device_del() will cleanup
> sysfs entries prior to device managed sysfs entries. This results
> in a NULL group->name and a system error during device cleanup.
> 
> To reproduce the issue, simply create a new child device in a
> platform driver of your choice. Add a sysfs file group using
> devm API.

What driver is doing this today?

> On driver exist ensure to unregister your child device.

What child device?  Why is a platform driver creating a child device at
all?

> Do not call devm_device_remove_group() and leave it up to the
> implementation to automatically clean up the files. Here is where
> you will see a kernel error complaining that the files have already
> been removed.
> 
> Signed-off-by: Daniel Steger <daniel.steger@...inx.com>
> ---
>  fs/sysfs/group.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/sysfs/group.c b/fs/sysfs/group.c
> index 64e6a6698935..023b40840f36 100644
> --- a/fs/sysfs/group.c
> +++ b/fs/sysfs/group.c
> @@ -286,9 +286,10 @@ void sysfs_remove_group(struct kobject *kobj,
>  		kernfs_get(kn);
>  	}
>  
> -	remove_files(kn, grp);
> -	if (grp->name)
> +	if (grp->name) {
> +		remove_files(kn, grp);

What about groups without names?  Will then now not be removed properly?
Why does the name matter here?

thanks,

greg k-h