Commit 74e83122 authored by Al Viro's avatar Al Viro
Browse files

saner handling of temporary namespaces 



mount_subtree() creates (and soon destroys) a temporary namespace,
so that automounts could function normally.  These beasts should
never become anyone's current namespaces; they don't, but it would
be better to make prevention of that more straightforward.  And
since they don't become anyone's current namespace, we don't need
to bother with reserving procfs inums for those.

Teach alloc_mnt_ns() to skip inum allocation if told so, adjust
put_mnt_ns() accordingly, make mount_subtree() use temporary
(anon) namespace.  is_anon_ns() checks if a namespace is such.

Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 3bd045cc

fs/mount.h

+5 −0
Original line number Diff line number Diff line
@@ -146,3 +146,8 @@ static inline bool is_local_mountpoint(struct dentry *dentry) 


	return __is_local_mountpoint(dentry);

}



static inline bool is_anon_ns(struct mnt_namespace *ns)

{

	return ns->seq == 0;

}

fs/namespace.c

+35 −39
Original line number Diff line number Diff line
@@ -2873,6 +2873,7 @@ static void dec_mnt_namespaces(struct ucounts *ucounts) 


static void free_mnt_ns(struct mnt_namespace *ns)

{

	if (!is_anon_ns(ns))

		ns_free_inum(&ns->ns);

	dec_mnt_namespaces(ns->ucounts);

	put_user_ns(ns->user_ns);
@@ -2888,7 +2889,7 @@ static void free_mnt_ns(struct mnt_namespace *ns) 
 */

static atomic64_t mnt_ns_seq = ATOMIC64_INIT(1);



static struct mnt_namespace *alloc_mnt_ns(struct user_namespace *user_ns)

static struct mnt_namespace *alloc_mnt_ns(struct user_namespace *user_ns, bool anon)

{

	struct mnt_namespace *new_ns;

	struct ucounts *ucounts;
@@ -2898,28 +2899,27 @@ static struct mnt_namespace *alloc_mnt_ns(struct user_namespace *user_ns) 
	if (!ucounts)

		return ERR_PTR(-ENOSPC);



	new_ns = kmalloc(sizeof(struct mnt_namespace), GFP_KERNEL);

	new_ns = kzalloc(sizeof(struct mnt_namespace), GFP_KERNEL);

	if (!new_ns) {

		dec_mnt_namespaces(ucounts);

		return ERR_PTR(-ENOMEM);

	}

	if (!anon) {

		ret = ns_alloc_inum(&new_ns->ns);

		if (ret) {

			kfree(new_ns);

			dec_mnt_namespaces(ucounts);

			return ERR_PTR(ret);

		}

	}

	new_ns->ns.ops = &mntns_operations;

	if (!anon)

		new_ns->seq = atomic64_add_return(1, &mnt_ns_seq);

	atomic_set(&new_ns->count, 1);

	new_ns->root = NULL;

	INIT_LIST_HEAD(&new_ns->list);

	init_waitqueue_head(&new_ns->poll);

	new_ns->event = 0;

	new_ns->user_ns = get_user_ns(user_ns);

	new_ns->ucounts = ucounts;

	new_ns->mounts = 0;

	new_ns->pending_mounts = 0;

	return new_ns;

}
@@ -2943,7 +2943,7 @@ struct mnt_namespace *copy_mnt_ns(unsigned long flags, struct mnt_namespace *ns, 


	old = ns->root;



	new_ns = alloc_mnt_ns(user_ns);

	new_ns = alloc_mnt_ns(user_ns, false);

	if (IS_ERR(new_ns))

		return new_ns;
@@ -3003,37 +3003,25 @@ struct mnt_namespace *copy_mnt_ns(unsigned long flags, struct mnt_namespace *ns, 
	return new_ns;

}



/**

 * create_mnt_ns - creates a private namespace and adds a root filesystem

 * @mnt: pointer to the new root filesystem mountpoint

 */

static struct mnt_namespace *create_mnt_ns(struct vfsmount *m)

struct dentry *mount_subtree(struct vfsmount *m, const char *name)

{

	struct mnt_namespace *new_ns = alloc_mnt_ns(&init_user_ns);

	if (!IS_ERR(new_ns)) {

	struct mount *mnt = real_mount(m);

		mnt->mnt_ns = new_ns;

		new_ns->root = mnt;

		new_ns->mounts++;

		list_add(&mnt->mnt_list, &new_ns->list);

	} else {

		mntput(m);

	}

	return new_ns;

}



struct dentry *mount_subtree(struct vfsmount *mnt, const char *name)

{

	struct mnt_namespace *ns;

	struct super_block *s;

	struct path path;

	int err;



	ns = create_mnt_ns(mnt);

	if (IS_ERR(ns))

	ns = alloc_mnt_ns(&init_user_ns, true);

	if (IS_ERR(ns)) {

		mntput(m);

		return ERR_CAST(ns);

	}

	mnt->mnt_ns = ns;

	ns->root = mnt;

	ns->mounts++;

	list_add(&mnt->mnt_list, &ns->list);



	err = vfs_path_lookup(mnt->mnt_root, mnt,

	err = vfs_path_lookup(m->mnt_root, m,

			name, LOOKUP_FOLLOW|LOOKUP_AUTOMOUNT, &path);



	put_mnt_ns(ns);
@@ -3243,6 +3231,7 @@ out0: 
static void __init init_mount_tree(void)

{

	struct vfsmount *mnt;

	struct mount *m;

	struct mnt_namespace *ns;

	struct path root;

	struct file_system_type *type;
@@ -3255,10 +3244,14 @@ static void __init init_mount_tree(void) 
	if (IS_ERR(mnt))

		panic("Can't create rootfs");



	ns = create_mnt_ns(mnt);

	ns = alloc_mnt_ns(&init_user_ns, false);

	if (IS_ERR(ns))

		panic("Can't allocate initial namespace");



	m = real_mount(mnt);

	m->mnt_ns = ns;

	ns->root = m;

	ns->mounts = 1;

	list_add(&m->mnt_list, &ns->list);

	init_task.nsproxy->mnt_ns = ns;

	get_mnt_ns(ns);
@@ -3499,6 +3492,9 @@ static int mntns_install(struct nsproxy *nsproxy, struct ns_common *ns) 
	    !ns_capable(current_user_ns(), CAP_SYS_ADMIN))

		return -EPERM;



	if (is_anon_ns(mnt_ns))

		return -EINVAL;



	if (fs->users != 1)

		return -EINVAL;

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