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SubjectRe: [PATCH net-next v3 2/9] sysfs: add sysfs_link_change_owner()
On Tue, Feb 18, 2020 at 05:29:36PM +0100, Christian Brauner wrote:
> Add a helper to change the owner of a sysfs link.
> This function will be used to correctly account for kobject ownership
> changes, e.g. when moving network devices between network namespaces.
>
> Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
> ---
> /* v2 */
> - Greg Kroah-Hartman <gregkh@linuxfoundation.org>:
> - Add comment how ownership of sysfs object is changed.
>
> /* v3 */
> - Greg Kroah-Hartman <gregkh@linuxfoundation.org>:
> - Add explicit uid/gid parameters.
> ---
> fs/sysfs/file.c | 40 ++++++++++++++++++++++++++++++++++++++++
> include/linux/sysfs.h | 10 ++++++++++
> 2 files changed, 50 insertions(+)
>
> diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
> index 32bb04b4d9d9..df5107d7b3fd 100644
> --- a/fs/sysfs/file.c
> +++ b/fs/sysfs/file.c
> @@ -570,6 +570,46 @@ static int internal_change_owner(struct kernfs_node *kn, struct kobject *kobj,
> return kernfs_setattr(kn, &newattrs);
> }
>
> +/**
> + * sysfs_link_change_owner - change owner of a link.
> + * @kobj: object of the kernfs_node the symlink is located in.
> + * @targ: object of the kernfs_node the symlink points to.
> + * @name: name of the link.
> + * @kuid: new owner's kuid
> + * @kgid: new owner's kgid
> + */
> +int sysfs_link_change_owner(struct kobject *kobj, struct kobject *targ,
> + const char *name, kuid_t kuid, kgid_t kgid)
> +{
> + struct kernfs_node *parent, *kn = NULL;
> + int error;
> +
> + if (!kobj)
> + parent = sysfs_root_kn;
> + else
> + parent = kobj->sd;

I don't understand this, why would (!kobj) ever be a valid situation?

> + if (!targ->state_in_sysfs)
> + return -EINVAL;

Should you also check kobj->state_in_sysfs as well?

thanks,

greg k-h

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