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>

10 files changed, 49 insertions, 38 deletions

diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index 8d40c4b1db9ff..be262145ae084 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -313,7 +313,8 @@ struct kernfs_node *kernfs_get_parent(struct kernfs_node *kn)
  *
  *	Return: 31-bit hash of ns + name (so it fits in an off_t)
  */
-static unsigned int kernfs_name_hash(const char *name, const void *ns)
+static unsigned int kernfs_name_hash(const char *name,
+				     const struct ns_common *ns)
 {
 	unsigned long hash = init_name_hash(ns);
 	unsigned int len = strlen(name);
@@ -330,7 +331,7 @@ static unsigned int kernfs_name_hash(const char *name, const void *ns)
 }
 
 static int kernfs_name_compare(unsigned int hash, const char *name,
-			       const void *ns, const struct kernfs_node *kn)
+			       const struct ns_common *ns, const struct kernfs_node *kn)
 {
 	if (hash < kn->hash)
 		return -1;
@@ -856,7 +857,7 @@ out_unlock:
  */
 static struct kernfs_node *kernfs_find_ns(struct kernfs_node *parent,
 					  const unsigned char *name,
-					  const void *ns)
+					  const struct ns_common *ns)
 {
 	struct rb_node *node = parent->dir.children.rb_node;
 	bool has_ns = kernfs_ns_enabled(parent);
@@ -889,7 +890,7 @@ static struct kernfs_node *kernfs_find_ns(struct kernfs_node *parent,
 
 static struct kernfs_node *kernfs_walk_ns(struct kernfs_node *parent,
 					  const unsigned char *path,
-					  const void *ns)
+					  const struct ns_common *ns)
 {
 	ssize_t len;
 	char *p, *name;
@@ -930,7 +931,8 @@ static struct kernfs_node *kernfs_walk_ns(struct kernfs_node *parent,
  * Return: pointer to the found kernfs_node on success, %NULL on failure.
  */
 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 *kn;
 	struct kernfs_root *root = kernfs_root(parent);
@@ -956,7 +958,8 @@ EXPORT_SYMBOL_GPL(kernfs_find_and_get_ns);
  * Return: pointer to the found kernfs_node on success, %NULL on failure.
  */
 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)
 {
 	struct kernfs_node *kn;
 	struct kernfs_root *root = kernfs_root(parent);
@@ -1079,7 +1082,8 @@ struct kernfs_node *kernfs_root_to_node(struct kernfs_root *root)
 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 *kn;
 	int rc;
@@ -1221,7 +1225,7 @@ static struct dentry *kernfs_iop_lookup(struct inode *dir,
 	struct kernfs_node *kn;
 	struct kernfs_root *root;
 	struct inode *inode = NULL;
-	const void *ns = NULL;
+	const struct ns_common *ns = NULL;
 
 	root = kernfs_root(parent);
 	down_read(&root->kernfs_rwsem);
@@ -1702,7 +1706,7 @@ bool kernfs_remove_self(struct kernfs_node *kn)
  * Return: %0 on success, -ENOENT if such entry doesn't exist.
  */
 int kernfs_remove_by_name_ns(struct kernfs_node *parent, const char *name,
-			     const void *ns)
+			     const struct ns_common *ns)
 {
 	struct kernfs_node *kn;
 	struct kernfs_root *root;
@@ -1741,7 +1745,7 @@ int kernfs_remove_by_name_ns(struct kernfs_node *parent, const char *name,
  * Return: %0 on success, -errno on failure.
  */
 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)
 {
 	struct kernfs_node *old_parent;
 	struct kernfs_root *root;
@@ -1832,7 +1836,7 @@ static int kernfs_dir_fop_release(struct inode *inode, struct file *filp)
 	return 0;
 }
 
-static struct kernfs_node *kernfs_dir_pos(const void *ns,
+static struct kernfs_node *kernfs_dir_pos(const struct ns_common *ns,
 	struct kernfs_node *parent, loff_t hash, struct kernfs_node *pos)
 {
 	if (pos) {
@@ -1867,7 +1871,7 @@ static struct kernfs_node *kernfs_dir_pos(const void *ns,
 	return pos;
 }
 
-static struct kernfs_node *kernfs_dir_next_pos(const void *ns,
+static struct kernfs_node *kernfs_dir_next_pos(const struct ns_common *ns,
 	struct kernfs_node *parent, ino_t ino, struct kernfs_node *pos)
 {
 	pos = kernfs_dir_pos(ns, parent, ino, pos);
@@ -1889,7 +1893,7 @@ static int kernfs_fop_readdir(struct file *file, struct dir_context *ctx)
 	struct kernfs_node *parent = kernfs_dentry_node(dentry);
 	struct kernfs_node *pos = file->private_data;
 	struct kernfs_root *root;
-	const void *ns = NULL;
+	const struct ns_common *ns = NULL;
 
 	if (!dir_emit_dots(file, ctx))
 		return 0;
diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
index e32406d62c0d3..1163aa7697384 100644
--- a/fs/kernfs/file.c
+++ b/fs/kernfs/file.c
@@ -1045,7 +1045,7 @@ struct kernfs_node *__kernfs_create_file(struct kernfs_node *parent,
 					 umode_t mode, 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 *kn;
diff --git a/fs/kernfs/kernfs-internal.h b/fs/kernfs/kernfs-internal.h
index 6061b6f70d2a3..b1fd9622a5e34 100644
--- a/fs/kernfs/kernfs-internal.h
+++ b/fs/kernfs/kernfs-internal.h
@@ -97,7 +97,7 @@ struct kernfs_super_info {
 	 * instance.  If multiple tags become necessary, make the following
 	 * an array and compare kernfs_node tag against every entry.
 	 */
-	const void		*ns;
+	const struct ns_common	*ns;
 
 	/* anchored at kernfs_root->supers, protected by kernfs_rwsem */
 	struct list_head	node;
diff --git a/fs/kernfs/mount.c b/fs/kernfs/mount.c
index 048f00b73b717..6e3217b6e4811 100644
--- a/fs/kernfs/mount.c
+++ b/fs/kernfs/mount.c
@@ -345,7 +345,7 @@ static int kernfs_set_super(struct super_block *sb, struct fs_context *fc)
  *
  * Return: the namespace tag associated with kernfs super_block @sb.
  */
-const void *kernfs_super_ns(struct super_block *sb)
+const struct ns_common *kernfs_super_ns(struct super_block *sb)
 {
 	struct kernfs_super_info *info = kernfs_info(sb);
 
diff --git a/fs/nfs/sysfs.c b/fs/nfs/sysfs.c
index 7d8921f524a69..1da4f707f9efe 100644
--- a/fs/nfs/sysfs.c
+++ b/fs/nfs/sysfs.c
@@ -11,6 +11,7 @@
 #include <linux/netdevice.h>
 #include <linux/string.h>
 #include <linux/nfs_fs.h>
+#include <net/net_namespace.h>
 #include <linux/rcupdate.h>
 #include <linux/lockd/lockd.h>
 
@@ -127,9 +128,10 @@ static void nfs_netns_client_release(struct kobject *kobj)
 	kfree(rcu_dereference_raw(c->identifier));
 }
 
-static const void *nfs_netns_client_namespace(const struct kobject *kobj)
+static const struct ns_common *nfs_netns_client_namespace(const struct kobject *kobj)
 {
-	return container_of(kobj, struct nfs_netns_client, kobject)->net;
+	return to_ns_common(container_of(kobj, struct nfs_netns_client,
+					 kobject)->net);
 }
 
 static struct kobj_attribute nfs_netns_client_id = __ATTR(identifier,
@@ -156,9 +158,10 @@ static void nfs_netns_object_release(struct kobject *kobj)
 	kfree(c);
 }
 
-static const void *nfs_netns_namespace(const struct kobject *kobj)
+static const struct ns_common *nfs_netns_namespace(const struct kobject *kobj)
 {
-	return container_of(kobj, struct nfs_netns_client, nfs_net_kobj)->net;
+	return to_ns_common(container_of(kobj, struct nfs_netns_client,
+					 nfs_net_kobj)->net);
 }
 
 static struct kobj_type nfs_netns_object_type = {
@@ -350,9 +353,10 @@ static void nfs_sysfs_sb_release(struct kobject *kobj)
 	/* no-op: why? see lib/kobject.c kobject_cleanup() */
 }
 
-static const void *nfs_netns_server_namespace(const struct kobject *kobj)
+static const struct ns_common *nfs_netns_server_namespace(const struct kobject *kobj)
 {
-	return container_of(kobj, struct nfs_server, kobj)->nfs_client->cl_net;
+	return to_ns_common(container_of(kobj, struct nfs_server,
+					 kobj)->nfs_client->cl_net);
 }
 
 static struct kobj_type nfs_sb_ktype = {
diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
index 94e12efd92f21..ffdcd4153c584 100644
--- a/fs/sysfs/dir.c
+++ b/fs/sysfs/dir.c
@@ -37,7 +37,7 @@ void sysfs_warn_dup(struct kernfs_node *parent, const char *name)
  * @kobj: object we're creating directory for
  * @ns: the namespace tag to use
  */
-int sysfs_create_dir_ns(struct kobject *kobj, const void *ns)
+int sysfs_create_dir_ns(struct kobject *kobj, const struct ns_common *ns)
 {
 	struct kernfs_node *parent, *kn;
 	kuid_t uid;
@@ -103,7 +103,7 @@ void sysfs_remove_dir(struct kobject *kobj)
 }
 
 int sysfs_rename_dir_ns(struct kobject *kobj, const char *new_name,
-			const void *new_ns)
+			const struct ns_common *new_ns)
 {
 	struct kernfs_node *parent;
 	int ret;
@@ -115,7 +115,7 @@ int sysfs_rename_dir_ns(struct kobject *kobj, const char *new_name,
 }
 
 int sysfs_move_dir_ns(struct kobject *kobj, struct kobject *new_parent_kobj,
-		      const void *new_ns)
+		      const struct ns_common *new_ns)
 {
 	struct kernfs_node *kn = kobj->sd;
 	struct kernfs_node *new_parent;
diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
index a8176c875f55e..5709cede1d756 100644
--- a/fs/sysfs/file.c
+++ b/fs/sysfs/file.c
@@ -272,7 +272,7 @@ static const struct kernfs_ops sysfs_bin_kfops_mmap = {
 
 int sysfs_add_file_mode_ns(struct kernfs_node *parent,
 		const struct attribute *attr, umode_t mode, kuid_t uid,
-		kgid_t gid, const void *ns)
+		kgid_t gid, const struct ns_common *ns)
 {
 	struct kobject *kobj = parent->priv;
 	const struct sysfs_ops *sysfs_ops = kobj->ktype->sysfs_ops;
@@ -322,7 +322,7 @@ int sysfs_add_file_mode_ns(struct kernfs_node *parent,
 
 int sysfs_add_bin_file_mode_ns(struct kernfs_node *parent,
 		const struct bin_attribute *battr, umode_t mode, size_t size,
-		kuid_t uid, kgid_t gid, const void *ns)
+		kuid_t uid, kgid_t gid, const struct ns_common *ns)
 {
 	const struct attribute *attr = &battr->attr;
 	struct lock_class_key *key = NULL;
@@ -362,7 +362,7 @@ int sysfs_add_bin_file_mode_ns(struct kernfs_node *parent,
  * @ns: namespace the new file should belong to
  */
 int sysfs_create_file_ns(struct kobject *kobj, const struct attribute *attr,
-			 const void *ns)
+			 const struct ns_common *ns)
 {
 	kuid_t uid;
 	kgid_t gid;
@@ -505,7 +505,7 @@ EXPORT_SYMBOL_GPL(sysfs_unbreak_active_protection);
  * Hash the attribute name and namespace tag and kill the victim.
  */
 void sysfs_remove_file_ns(struct kobject *kobj, const struct attribute *attr,
-			  const void *ns)
+			  const struct ns_common *ns)
 {
 	struct kernfs_node *parent = kobj->sd;
 
diff --git a/fs/sysfs/mount.c b/fs/sysfs/mount.c
index e65c60158a04a..b199e8ff79b1f 100644
--- a/fs/sysfs/mount.c
+++ b/fs/sysfs/mount.c
@@ -55,7 +55,7 @@ static const struct fs_context_operations sysfs_fs_context_ops = {
 static int sysfs_init_fs_context(struct fs_context *fc)
 {
 	struct kernfs_fs_context *kfc;
-	struct net *netns;
+	struct ns_common *ns;
 
 	if (!(fc->sb_flags & SB_KERNMOUNT)) {
 		if (!kobj_ns_current_may_mount(KOBJ_NS_TYPE_NET))
@@ -66,12 +66,14 @@ static int sysfs_init_fs_context(struct fs_context *fc)
 	if (!kfc)
 		return -ENOMEM;
 
-	kfc->ns_tag = netns = kobj_ns_grab_current(KOBJ_NS_TYPE_NET);
+	kfc->ns_tag = ns = kobj_ns_grab_current(KOBJ_NS_TYPE_NET);
 	kfc->root = sysfs_root;
 	kfc->magic = SYSFS_MAGIC;
 	fc->fs_private = kfc;
 	fc->ops = &sysfs_fs_context_ops;
-	if (netns) {
+	if (ns) {
+		struct net *netns = to_net_ns(ns);
+
 		put_user_ns(fc->user_ns);
 		fc->user_ns = get_user_ns(netns->user_ns);
 	}
@@ -81,7 +83,7 @@ static int sysfs_init_fs_context(struct fs_context *fc)
 
 static void sysfs_kill_sb(struct super_block *sb)
 {
-	void *ns = (void *)kernfs_super_ns(sb);
+	struct ns_common *ns = (struct ns_common *)kernfs_super_ns(sb);
 
 	kernfs_kill_sb(sb);
 	kobj_ns_drop(KOBJ_NS_TYPE_NET, ns);
diff --git a/fs/sysfs/symlink.c b/fs/sysfs/symlink.c
index 5603530a1a520..5f9c05fb13940 100644
--- a/fs/sysfs/symlink.c
+++ b/fs/sysfs/symlink.c
@@ -121,7 +121,7 @@ EXPORT_SYMBOL_GPL(sysfs_create_link_nowarn);
 void sysfs_delete_link(struct kobject *kobj, struct kobject *targ,
 			const char *name)
 {
-	const void *ns = NULL;
+	const struct ns_common *ns = NULL;
 
 	/*
 	 * We don't own @target and it may be removed at any time.
@@ -164,10 +164,11 @@ EXPORT_SYMBOL_GPL(sysfs_remove_link);
  *	A helper function for the common rename symlink idiom.
  */
 int sysfs_rename_link_ns(struct kobject *kobj, struct kobject *targ,
-			 const char *old, const char *new, const void *new_ns)
+			 const char *old, const char *new,
+			 const struct ns_common *new_ns)
 {
 	struct kernfs_node *parent, *kn = NULL;
-	const void *old_ns = NULL;
+	const struct ns_common *old_ns = NULL;
 	int result;
 
 	if (!kobj)
diff --git a/fs/sysfs/sysfs.h b/fs/sysfs/sysfs.h
index 8e012f25e1c06..f4583dcafcd1e 100644
--- a/fs/sysfs/sysfs.h
+++ b/fs/sysfs/sysfs.h
@@ -29,10 +29,10 @@ void sysfs_warn_dup(struct kernfs_node *parent, const char *name);
  */
 int sysfs_add_file_mode_ns(struct kernfs_node *parent,
 		const struct attribute *attr, umode_t amode, kuid_t uid,
-		kgid_t gid, const void *ns);
+		kgid_t gid, const struct ns_common *ns);
 int sysfs_add_bin_file_mode_ns(struct kernfs_node *parent,
 		const struct bin_attribute *battr, umode_t mode, size_t size,
-		kuid_t uid, kgid_t gid, const void *ns);
+		kuid_t uid, kgid_t gid, const struct ns_common *ns);
 
 /*
  * symlink.c