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>

6 files changed, 50 insertions, 41 deletions

diff --git a/include/linux/device/class.h b/include/linux/device/class.h
index 65880e60c720..021da0d61796 100644
--- a/include/linux/device/class.h
+++ b/include/linux/device/class.h
@@ -62,7 +62,7 @@ struct class {
 	int (*shutdown_pre)(struct device *dev);
 
 	const struct kobj_ns_type_operations *ns_type;
-	const void *(*namespace)(const struct device *dev);
+	const struct ns_common *(*namespace)(const struct device *dev);
 
 	void (*get_ownership)(const struct device *dev, kuid_t *uid, kgid_t *gid);
 
@@ -180,9 +180,9 @@ struct class_attribute {
 	struct class_attribute class_attr_##_name = __ATTR_WO(_name)
 
 int __must_check class_create_file_ns(const struct class *class, const struct class_attribute *attr,
-				      const void *ns);
+				      const struct ns_common *ns);
 void class_remove_file_ns(const struct class *class, const struct class_attribute *attr,
-			  const void *ns);
+			  const struct ns_common *ns);
 
 static inline int __must_check class_create_file(const struct class *class,
 						 const struct class_attribute *attr)
diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
index b5a5f32fdfd1..4f0ab88a1b31 100644
--- a/include/linux/kernfs.h
+++ b/include/linux/kernfs.h
@@ -23,6 +23,7 @@
 struct file;
 struct dentry;
 struct iattr;
+struct ns_common;
 struct seq_file;
 struct vm_area_struct;
 struct vm_operations_struct;
@@ -209,7 +210,7 @@ struct kernfs_node {
 
 	struct rb_node		rb;
 
-	const void		*ns;	/* namespace tag */
+	const struct ns_common	*ns;	/* namespace tag */
 	unsigned int		hash;	/* ns + name hash */
 	unsigned short		flags;
 	umode_t			mode;
@@ -331,7 +332,7 @@ struct kernfs_ops {
  */
 struct kernfs_fs_context {
 	struct kernfs_root	*root;		/* Root of the hierarchy being mounted */
-	void			*ns_tag;	/* Namespace tag of the mount (or NULL) */
+	struct ns_common	*ns_tag;	/* Namespace tag of the mount (or NULL) */
 	unsigned long		magic;		/* File system specific magic number */
 
 	/* The following are set/used by kernfs_mount() */
@@ -406,9 +407,11 @@ void pr_cont_kernfs_name(struct kernfs_node *kn);
 void pr_cont_kernfs_path(struct kernfs_node *kn);
 struct kernfs_node *kernfs_get_parent(struct kernfs_node *kn);
 struct kernfs_node *kernfs_find_and_get_ns(struct kernfs_node *parent,
-					   const char *name, const void *ns);
+					   const char *name,
+					   const struct ns_common *ns);
 struct kernfs_node *kernfs_walk_and_get_ns(struct kernfs_node *parent,
-					   const char *path, const void *ns);
+					   const char *path,
+					   const struct ns_common *ns);
 void kernfs_get(struct kernfs_node *kn);
 void kernfs_put(struct kernfs_node *kn);
 
@@ -426,7 +429,8 @@ unsigned int kernfs_root_flags(struct kernfs_node *kn);
 struct kernfs_node *kernfs_create_dir_ns(struct kernfs_node *parent,
 					 const char *name, umode_t mode,
 					 kuid_t uid, kgid_t gid,
-					 void *priv, const void *ns);
+					 void *priv,
+					 const struct ns_common *ns);
 struct kernfs_node *kernfs_create_empty_dir(struct kernfs_node *parent,
 					    const char *name);
 struct kernfs_node *__kernfs_create_file(struct kernfs_node *parent,
@@ -434,7 +438,8 @@ struct kernfs_node *__kernfs_create_file(struct kernfs_node *parent,
 					 kuid_t uid, kgid_t gid,
 					 loff_t size,
 					 const struct kernfs_ops *ops,
-					 void *priv, const void *ns,
+					 void *priv,
+					 const struct ns_common *ns,
 					 struct lock_class_key *key);
 struct kernfs_node *kernfs_create_link(struct kernfs_node *parent,
 				       const char *name,
@@ -446,9 +451,9 @@ void kernfs_break_active_protection(struct kernfs_node *kn);
 void kernfs_unbreak_active_protection(struct kernfs_node *kn);
 bool kernfs_remove_self(struct kernfs_node *kn);
 int kernfs_remove_by_name_ns(struct kernfs_node *parent, const char *name,
-			     const void *ns);
+			     const struct ns_common *ns);
 int kernfs_rename_ns(struct kernfs_node *kn, struct kernfs_node *new_parent,
-		     const char *new_name, const void *new_ns);
+		     const char *new_name, const struct ns_common *new_ns);
 int kernfs_setattr(struct kernfs_node *kn, const struct iattr *iattr);
 __poll_t kernfs_generic_poll(struct kernfs_open_file *of,
 			     struct poll_table_struct *pt);
@@ -459,7 +464,7 @@ int kernfs_xattr_get(struct kernfs_node *kn, const char *name,
 int kernfs_xattr_set(struct kernfs_node *kn, const char *name,
 		     const void *value, size_t size, int flags);
 
-const void *kernfs_super_ns(struct super_block *sb);
+const struct ns_common *kernfs_super_ns(struct super_block *sb);
 int kernfs_get_tree(struct fs_context *fc);
 void kernfs_free_fs_context(struct fs_context *fc);
 void kernfs_kill_sb(struct super_block *sb);
@@ -494,11 +499,11 @@ static inline struct kernfs_node *kernfs_get_parent(struct kernfs_node *kn)
 
 static inline struct kernfs_node *
 kernfs_find_and_get_ns(struct kernfs_node *parent, const char *name,
-		       const void *ns)
+		       const struct ns_common *ns)
 { return NULL; }
 static inline struct kernfs_node *
 kernfs_walk_and_get_ns(struct kernfs_node *parent, const char *path,
-		       const void *ns)
+		       const struct ns_common *ns)
 { return NULL; }
 
 static inline void kernfs_get(struct kernfs_node *kn) { }
@@ -526,14 +531,15 @@ static inline unsigned int kernfs_root_flags(struct kernfs_node *kn)
 static inline struct kernfs_node *
 kernfs_create_dir_ns(struct kernfs_node *parent, const char *name,
 		     umode_t mode, kuid_t uid, kgid_t gid,
-		     void *priv, const void *ns)
+		     void *priv, const struct ns_common *ns)
 { return ERR_PTR(-ENOSYS); }
 
 static inline struct kernfs_node *
 __kernfs_create_file(struct kernfs_node *parent, const char *name,
 		     umode_t mode, kuid_t uid, kgid_t gid,
 		     loff_t size, const struct kernfs_ops *ops,
-		     void *priv, const void *ns, struct lock_class_key *key)
+		     void *priv, const struct ns_common *ns,
+		     struct lock_class_key *key)
 { return ERR_PTR(-ENOSYS); }
 
 static inline struct kernfs_node *
@@ -549,12 +555,14 @@ static inline bool kernfs_remove_self(struct kernfs_node *kn)
 { return false; }
 
 static inline int kernfs_remove_by_name_ns(struct kernfs_node *kn,
-					   const char *name, const void *ns)
+					   const char *name,
+					   const struct ns_common *ns)
 { return -ENOSYS; }
 
 static inline int kernfs_rename_ns(struct kernfs_node *kn,
 				   struct kernfs_node *new_parent,
-				   const char *new_name, const void *new_ns)
+				   const char *new_name,
+				   const struct ns_common *new_ns)
 { return -ENOSYS; }
 
 static inline int kernfs_setattr(struct kernfs_node *kn,
@@ -575,7 +583,7 @@ static inline int kernfs_xattr_set(struct kernfs_node *kn, const char *name,
 				   const void *value, size_t size, int flags)
 { return -ENOSYS; }
 
-static inline const void *kernfs_super_ns(struct super_block *sb)
+static inline const struct ns_common *kernfs_super_ns(struct super_block *sb)
 { return NULL; }
 
 static inline int kernfs_get_tree(struct fs_context *fc)
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);
 };
 
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 */
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 7ca01eb3f7d2..85c20bdd36fb 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -5339,9 +5339,9 @@ static inline netdev_tx_t netdev_start_xmit(struct sk_buff *skb, struct net_devi
 }
 
 int netdev_class_create_file_ns(const struct class_attribute *class_attr,
-				const void *ns);
+				const struct ns_common *ns);
 void netdev_class_remove_file_ns(const struct class_attribute *class_attr,
-				 const void *ns);
+				 const struct ns_common *ns);
 
 extern const struct kobj_ns_type_operations net_ns_type_operations;
 
diff --git a/include/linux/sysfs.h b/include/linux/sysfs.h
index 99b775f3ff46..468259fb6049 100644
--- a/include/linux/sysfs.h
+++ b/include/linux/sysfs.h
@@ -396,13 +396,13 @@ struct sysfs_ops {
 
 #ifdef CONFIG_SYSFS
 
-int __must_check sysfs_create_dir_ns(struct kobject *kobj, const void *ns);
+int __must_check sysfs_create_dir_ns(struct kobject *kobj, const struct ns_common *ns);
 void sysfs_remove_dir(struct kobject *kobj);
 int __must_check sysfs_rename_dir_ns(struct kobject *kobj, const char *new_name,
-				     const void *new_ns);
+				     const struct ns_common *new_ns);
 int __must_check sysfs_move_dir_ns(struct kobject *kobj,
 				   struct kobject *new_parent_kobj,
-				   const void *new_ns);
+				   const struct ns_common *new_ns);
 int __must_check sysfs_create_mount_point(struct kobject *parent_kobj,
 					  const char *name);
 void sysfs_remove_mount_point(struct kobject *parent_kobj,
@@ -410,7 +410,7 @@ void sysfs_remove_mount_point(struct kobject *parent_kobj,
 
 int __must_check sysfs_create_file_ns(struct kobject *kobj,
 				      const struct attribute *attr,
-				      const void *ns);
+				      const struct ns_common *ns);
 int __must_check sysfs_create_files(struct kobject *kobj,
 				   const struct attribute * const *attr);
 int __must_check sysfs_chmod_file(struct kobject *kobj,
@@ -419,7 +419,7 @@ struct kernfs_node *sysfs_break_active_protection(struct kobject *kobj,
 						  const struct attribute *attr);
 void sysfs_unbreak_active_protection(struct kernfs_node *kn);
 void sysfs_remove_file_ns(struct kobject *kobj, const struct attribute *attr,
-			  const void *ns);
+			  const struct ns_common *ns);
 bool sysfs_remove_file_self(struct kobject *kobj, const struct attribute *attr);
 void sysfs_remove_files(struct kobject *kobj, const struct attribute * const *attr);
 
@@ -437,7 +437,7 @@ void sysfs_remove_link(struct kobject *kobj, const char *name);
 
 int sysfs_rename_link_ns(struct kobject *kobj, struct kobject *target,
 			 const char *old_name, const char *new_name,
-			 const void *new_ns);
+			 const struct ns_common *new_ns);
 
 void sysfs_delete_link(struct kobject *dir, struct kobject *targ,
 			const char *name);
@@ -502,7 +502,7 @@ ssize_t sysfs_bin_attr_simple_read(struct file *file, struct kobject *kobj,
 
 #else /* CONFIG_SYSFS */
 
-static inline int sysfs_create_dir_ns(struct kobject *kobj, const void *ns)
+static inline int sysfs_create_dir_ns(struct kobject *kobj, const struct ns_common *ns)
 {
 	return 0;
 }
@@ -512,14 +512,14 @@ static inline void sysfs_remove_dir(struct kobject *kobj)
 }
 
 static inline int sysfs_rename_dir_ns(struct kobject *kobj,
-				      const char *new_name, const void *new_ns)
+				      const char *new_name, const struct ns_common *new_ns)
 {
 	return 0;
 }
 
 static inline int sysfs_move_dir_ns(struct kobject *kobj,
 				    struct kobject *new_parent_kobj,
-				    const void *new_ns)
+				    const struct ns_common *new_ns)
 {
 	return 0;
 }
@@ -537,7 +537,7 @@ static inline void sysfs_remove_mount_point(struct kobject *parent_kobj,
 
 static inline int sysfs_create_file_ns(struct kobject *kobj,
 				       const struct attribute *attr,
-				       const void *ns)
+				       const struct ns_common *ns)
 {
 	return 0;
 }
@@ -567,7 +567,7 @@ static inline void sysfs_unbreak_active_protection(struct kernfs_node *kn)
 
 static inline void sysfs_remove_file_ns(struct kobject *kobj,
 					const struct attribute *attr,
-					const void *ns)
+					const struct ns_common *ns)
 {
 }
 
@@ -612,7 +612,7 @@ static inline void sysfs_remove_link(struct kobject *kobj, const char *name)
 
 static inline int sysfs_rename_link_ns(struct kobject *k, struct kobject *t,
 				       const char *old_name,
-				       const char *new_name, const void *ns)
+				       const char *new_name, const struct ns_common *ns)
 {
 	return 0;
 }