sysfs: add sysfs_file_change_owner()

Add helpers to change the owner of a sysfs files.
This function will be used to correctly account for kobject ownership
changes, e.g. when moving network devices between network namespaces.

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 47 insertions, 0 deletions

diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
index 130fc6fbcc038b..4ca936ca3ba447 100644
--- a/fs/sysfs/file.c
+++ b/fs/sysfs/file.c
@@ -558,3 +558,50 @@ void sysfs_remove_bin_file(struct kobject *kobj,
 	kernfs_remove_by_name(kobj->sd, attr->attr.name);
 }
 EXPORT_SYMBOL_GPL(sysfs_remove_bin_file);
+
+static int internal_change_owner(struct kernfs_node *kn, kuid_t kuid,
+				 kgid_t kgid)
+{
+	struct iattr newattrs = {
+		.ia_valid = ATTR_UID | ATTR_GID,
+		.ia_uid = kuid,
+		.ia_gid = kgid,
+	};
+	return kernfs_setattr(kn, &newattrs);
+}
+
+/**
+ *	sysfs_file_change_owner - change owner of a sysfs file.
+ *	@kobj:	object.
+ *	@name:	name of the file to change.
+ *	@kuid:	new owner's kuid
+ *	@kgid:	new owner's kgid
+ *
+ * This function looks up the sysfs entry @name under @kobj and changes the
+ * ownership to @kuid/@kgid.
+ *
+ * Returns 0 on success or error code on failure.
+ */
+int sysfs_file_change_owner(struct kobject *kobj, const char *name, kuid_t kuid,
+			    kgid_t kgid)
+{
+	struct kernfs_node *kn;
+	int error;
+
+	if (!name)
+		return -EINVAL;
+
+	if (!kobj->state_in_sysfs)
+		return -EINVAL;
+
+	kn = kernfs_find_and_get(kobj->sd, name);
+	if (!kn)
+		return -ENOENT;
+
+	error = internal_change_owner(kn, kuid, kgid);
+
+	kernfs_put(kn);
+
+	return error;
+}
+EXPORT_SYMBOL_GPL(sysfs_file_change_owner);