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, 7 insertions, 6 deletions

diff --git a/include/linux/kobject_ns.h b/include/linux/kobject_ns.h
index 150fe2ae1b6b..4f0990e09b93 100644
--- a/include/linux/kobject_ns.h
+++ b/include/linux/kobject_ns.h
@@ -16,6 +16,7 @@
 #ifndef _LINUX_KOBJECT_NS_H
 #define _LINUX_KOBJECT_NS_H
 
+struct ns_common;
 struct sock;
 struct kobject;
 
@@ -39,10 +40,10 @@ enum kobj_ns_type {
 struct kobj_ns_type_operations {
 	enum kobj_ns_type type;
 	bool (*current_may_mount)(void);
-	void *(*grab_current_ns)(void);
-	const void *(*netlink_ns)(struct sock *sk);
-	const void *(*initial_ns)(void);
-	void (*drop_ns)(void *);
+	struct ns_common *(*grab_current_ns)(void);
+	const struct ns_common *(*netlink_ns)(struct sock *sk);
+	const struct ns_common *(*initial_ns)(void);
+	void (*drop_ns)(struct ns_common *);
 };
 
 int kobj_ns_type_register(const struct kobj_ns_type_operations *ops);
@@ -51,7 +52,7 @@ const struct kobj_ns_type_operations *kobj_child_ns_ops(const struct kobject *pa
 const struct kobj_ns_type_operations *kobj_ns_ops(const struct kobject *kobj);
 
 bool kobj_ns_current_may_mount(enum kobj_ns_type type);
-void *kobj_ns_grab_current(enum kobj_ns_type type);
-void kobj_ns_drop(enum kobj_ns_type type, void *ns);
+struct ns_common *kobj_ns_grab_current(enum kobj_ns_type type);
+void kobj_ns_drop(enum kobj_ns_type type, struct ns_common *ns);
 
 #endif /* _LINUX_KOBJECT_NS_H */