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>

5 files changed, 19 insertions, 16 deletions

diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
index 94e12efd92f2..ffdcd4153c58 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 a8176c875f55..5709cede1d75 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 e65c60158a04..b199e8ff79b1 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 5603530a1a52..5f9c05fb1394 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 8e012f25e1c0..f4583dcafcd1 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