fs: move mnt_idmap

Now that we converted everything to just rely on struct mnt_idmap move it all
into a separate file. This ensure that no code can poke around in struct
mnt_idmap without any dedicated helpers and makes it easier to extend it in the
future. Filesystems will now not be able to conflate mount and filesystem
idmappings as they are two distinct types and require distinct helpers that
cannot be used interchangeably. We are now also able to extend struct mnt_idmap
as we see fit.

Acked-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>

1 files changed, 2 insertions, 90 deletions

diff --git a/fs/namespace.c b/fs/namespace.c
index b7a2af5c896e..5927d90e24a0 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -75,22 +75,6 @@ static DECLARE_RWSEM(namespace_sem);
 static HLIST_HEAD(unmounted);	/* protected by namespace_sem */
 static LIST_HEAD(ex_mountpoints); /* protected by namespace_sem */
 
-struct mnt_idmap {
-	struct user_namespace *owner;
-	refcount_t count;
-};
-
-/*
- * Carries the initial idmapping of 0:0:4294967295 which is an identity
- * mapping. This means that {g,u}id 0 is mapped to {g,u}id 0, {g,u}id 1 is
- * mapped to {g,u}id 1, [...], {g,u}id 1000 to {g,u}id 1000, [...].
- */
-struct mnt_idmap nop_mnt_idmap = {
-	.owner	= &init_user_ns,
-	.count	= REFCOUNT_INIT(1),
-};
-EXPORT_SYMBOL_GPL(nop_mnt_idmap);
-
 struct mount_kattr {
 	unsigned int attr_set;
 	unsigned int attr_clr;
@@ -210,78 +194,6 @@ int mnt_get_count(struct mount *mnt)
 #endif
 }
 
-/**
- * mnt_idmap_owner - retrieve owner of the mount's idmapping
- * @idmap: mount idmapping
- *
- * This helper will go away once the conversion to use struct mnt_idmap
- * everywhere has finished at which point the helper will be unexported.
- *
- * Only code that needs to perform permission checks based on the owner of the
- * idmapping will get access to it. All other code will solely rely on
- * idmappings. This will get us type safety so it's impossible to conflate
- * filesystems idmappings with mount idmappings.
- *
- * Return: The owner of the idmapping.
- */
-struct user_namespace *mnt_idmap_owner(const struct mnt_idmap *idmap)
-{
-	return idmap->owner;
-}
-EXPORT_SYMBOL_GPL(mnt_idmap_owner);
-
-/**
- * alloc_mnt_idmap - allocate a new idmapping for the mount
- * @mnt_userns: owning userns of the idmapping
- *
- * Allocate a new struct mnt_idmap which carries the idmapping of the mount.
- *
- * Return: On success a new idmap, on error an error pointer is returned.
- */
-static struct mnt_idmap *alloc_mnt_idmap(struct user_namespace *mnt_userns)
-{
-	struct mnt_idmap *idmap;
-
-	idmap = kzalloc(sizeof(struct mnt_idmap), GFP_KERNEL_ACCOUNT);
-	if (!idmap)
-		return ERR_PTR(-ENOMEM);
-
-	idmap->owner = get_user_ns(mnt_userns);
-	refcount_set(&idmap->count, 1);
-	return idmap;
-}
-
-/**
- * mnt_idmap_get - get a reference to an idmapping
- * @idmap: the idmap to bump the reference on
- *
- * If @idmap is not the @nop_mnt_idmap bump the reference count.
- *
- * Return: @idmap with reference count bumped if @not_mnt_idmap isn't passed.
- */
-static inline struct mnt_idmap *mnt_idmap_get(struct mnt_idmap *idmap)
-{
-	if (idmap != &nop_mnt_idmap)
-		refcount_inc(&idmap->count);
-
-	return idmap;
-}
-
-/**
- * mnt_idmap_put - put a reference to an idmapping
- * @idmap: the idmap to put the reference on
- *
- * If this is a non-initial idmapping, put the reference count when a mount is
- * released and free it if we're the last user.
- */
-static inline void mnt_idmap_put(struct mnt_idmap *idmap)
-{
-	if (idmap != &nop_mnt_idmap && refcount_dec_and_test(&idmap->count)) {
-		put_user_ns(idmap->owner);
-		kfree(idmap);
-	}
-}
-
 static struct mount *alloc_vfsmnt(const char *name)
 {
 	struct mount *mnt = kmem_cache_zalloc(mnt_cache, GFP_KERNEL);
@@ -4068,7 +3980,7 @@ static int can_idmap_mount(const struct mount_kattr *kattr, struct mount *mnt)
 	 * Creating an idmapped mount with the filesystem wide idmapping
 	 * doesn't make sense so block that. We don't allow mushy semantics.
 	 */
-	if (mnt_idmap_owner(kattr->mnt_idmap) == fs_userns)
+	if (!check_fsmapping(kattr->mnt_idmap, m->mnt_sb))
 		return -EINVAL;
 
 	/*
@@ -4314,7 +4226,7 @@ static int build_mount_idmapped(const struct mount_attr *attr, size_t usize,
 	 * result.
 	 */
 	mnt_userns = container_of(ns, struct user_namespace, ns);
-	if (initial_idmapping(mnt_userns)) {
+	if (mnt_userns == &init_user_ns) {
 		err = -EPERM;
 		goto out_fput;
 	}