linux-kernel - Re: [PATCH v5 68/68] sysfs(2): fs_index() argument is _not

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Message-ID: <20260114104155.708180fc@pumpkin>
Date: Wed, 14 Jan 2026 10:41:55 +0000
From: David Laight <david.laight.linux@...il.com>
To: Al Viro <viro@...iv.linux.org.uk>
Cc: linux-fsdevel@...r.kernel.org, Linus Torvalds
 <torvalds@...ux-foundation.org>, Christian Brauner <brauner@...nel.org>,
 Jan Kara <jack@...e.cz>, Mateusz Guzik <mjguzik@...il.com>, Paul Moore
 <paul@...l-moore.com>, Jens Axboe <axboe@...nel.dk>, audit@...r.kernel.org,
 io-uring@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 68/68] sysfs(2): fs_index() argument is _not_ a
 pathname

On Wed, 14 Jan 2026 04:33:10 +0000
Al Viro <viro@...iv.linux.org.uk> wrote:

> ... it's a filesystem type name.
> 
> Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
> ---
>  fs/filesystems.c | 9 +++------
>  1 file changed, 3 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/filesystems.c b/fs/filesystems.c
> index 95e5256821a5..0c7d2b7ac26c 100644
> --- a/fs/filesystems.c
> +++ b/fs/filesystems.c
> @@ -132,24 +132,21 @@ EXPORT_SYMBOL(unregister_filesystem);
>  static int fs_index(const char __user * __name)
>  {
>  	struct file_system_type * tmp;
> -	struct filename *name;
> +	char *name __free(kfree) = strndup_user(__name, PATH_MAX);
>  	int err, index;
>  
> -	name = getname(__name);
> -	err = PTR_ERR(name);
>  	if (IS_ERR(name))
> -		return err;
> +		return PTR_ERR(name);

Doesn't that end up calling kfree(name) and the check in kfree() doesn't
seem to exclude error values.

Changing:
#define ZERO_OR_NULL_PTR(x) ((unsigned long)(x) <= \
				(unsigned long)ZERO_SIZE_PTR)
to:
#define ZERO_OR_NULL_PTR(x) (4096 + (unsigned long)(x) <= \
				4096 + (unsigned long)ZERO_SIZE_PTR)
would fix it at minimal cost.

	David


>  
>  	err = -EINVAL;
>  	read_lock(&file_systems_lock);
>  	for (tmp=file_systems, index=0 ; tmp ; tmp=tmp->next, index++) {
> -		if (strcmp(tmp->name, name->name) == 0) {
> +		if (strcmp(tmp->name, name) == 0) {
>  			err = index;
>  			break;
>  		}
>  	}
>  	read_unlock(&file_systems_lock);
> -	putname(name);
>  	return err;
>  }
>