kernfs: pass struct ns_common instead of const void * for namespace tags

kernfs has historically used const void * to pass around namespace tags
used for directory-level namespace filtering. The only current user of
this is sysfs network namespace tagging where struct net pointers are
cast to void *.

Replace all const void * namespace parameters with const struct
ns_common * throughout the kernfs, sysfs, and kobject namespace layers.
This includes the kobj_ns_type_operations callbacks, kobject_namespace(),
and all sysfs/kernfs APIs that accept or return namespace tags.

Passing struct ns_common is needed because various codepaths require
access to the underlying namespace. A struct ns_common can always be
converted back to the concrete namespace type (e.g., struct net) via
container_of() or to_ns_common() in the reverse direction.

This is a preparatory change for switching to ns_id-based directory
iteration to prevent a KASLR pointer leak through the current use of
raw namespace pointers as hash seeds and comparison keys.

Signed-off-by: Christian Brauner <brauner@kernel.org>

1 files changed, 2 insertions, 2 deletions

diff --git a/include/linux/kobject.h b/include/linux/kobject.h
index c8219505a79f..bcb5d4e32001 100644
--- a/include/linux/kobject.h
+++ b/include/linux/kobject.h
@@ -109,7 +109,7 @@ struct kobject *kobject_get(struct kobject *kobj);
 struct kobject * __must_check kobject_get_unless_zero(struct kobject *kobj);
 void kobject_put(struct kobject *kobj);
 
-const void *kobject_namespace(const struct kobject *kobj);
+const struct ns_common *kobject_namespace(const struct kobject *kobj);
 void kobject_get_ownership(const struct kobject *kobj, kuid_t *uid, kgid_t *gid);
 char *kobject_get_path(const struct kobject *kobj, gfp_t flag);
 
@@ -118,7 +118,7 @@ struct kobj_type {
 	const struct sysfs_ops *sysfs_ops;
 	const struct attribute_group **default_groups;
 	const struct kobj_ns_type_operations *(*child_ns_type)(const struct kobject *kobj);
-	const void *(*namespace)(const struct kobject *kobj);
+	const struct ns_common *(*namespace)(const struct kobject *kobj);
 	void (*get_ownership)(const struct kobject *kobj, kuid_t *uid, kgid_t *gid);
 };