Re: [PATCH] configfs: fix refcount warning in configfs_get_config_item()

[Joshua Crofts <joshua.crofts1@gmail.com>]

On Wed, 29 Jul 2026 08:55:05 +0000
Joshua Crofts <joshua.crofts1@gmail.com> wrote:

> syzbot reported a "refcount_t: addition on 0; use-after-free" warning
> in configfs_get_config_item().
> 
> This occurs when configfs_get_config_item() races with a concurrent
> teardown (e.g. rmdir). When the target config_item's refcount drops to
> 0, configfs_get_config_item() calls config_item_get(), which
> unconditionally increments the refcount via kref_get(), triggering the
> refcount warning.
> 
> Fix this by using config_item_get_unless_zero(), which safely returns
> NULL if the refcount is already 0.
> 
> Reported-by: syzbot+35790eb7861f8fc57382@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=35790eb7861f8fc57382
> Signed-off-by: Joshua Crofts <joshua.crofts1@gmail.com>
> ---
>  fs/configfs/configfs_internal.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/configfs/configfs_internal.h b/fs/configfs/configfs_internal.h
> index acdeea8e2..5448af3a8 100644
> --- a/fs/configfs/configfs_internal.h
> +++ b/fs/configfs/configfs_internal.h
> @@ -124,7 +124,7 @@ static inline struct config_item *configfs_get_config_item(struct dentry *dentry
>  	spin_lock(&dentry->d_lock);
>  	if (!d_unhashed(dentry)) {
>  		struct configfs_dirent * sd = dentry->d_fsdata;
> -		item = config_item_get(sd->s_element);
> +		item = config_item_get_unless_zero(sd->s_element);
>  	}
>  	spin_unlock(&dentry->d_lock);
>  

Forgot to add a Fixes: tag so here it is, will respin if necessary:

Fixes: e9c03af21cc7 ("configfs: calculate the symlink target only once")

-- 
Kind regards,
Joshua Crofts