Merge branch 'work.mount' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs

Pull vfs mount infrastructure updates from Al Viro: "The rest of core infrastructure; no new syscalls in that pile, but the old parts are switched to new infrastructure. At that point conversions of individual filesystems can happen independently; some are done here (afs, cgroup, procfs, etc.), there's also a large series outside of that pile dealing with NFS (quite a bit of option-parsing stuff is getting used there - it's one of the most convoluted filesystems in terms of mount-related logics), but NFS bits are the next cycle fodder. It got seriously simplified since the last cycle; documentation is probably the weakest bit at the moment - I considered dropping the commit introducing Documentation/filesystems/mount_api.txt (cutting the size increase by quarter ;-), but decided that it would be better to fix it up after -rc1 instead. That pile allows to do followup work in independent branches, which should make life much easier for the next cycle. fs/super.c size increase is unpleasant; there's a followup series that allows to shrink it considerably, but I decided to leave that until the next cycle" * 'work.mount' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: (41 commits) afs: Use fs_context to pass parameters over automount afs: Add fs_context support vfs: Add some logging to the core users of the fs_context log vfs: Implement logging through fs_context vfs: Provide documentation for new mount API vfs: Remove kern_mount_data() hugetlbfs: Convert to fs_context cpuset: Use fs_context kernfs, sysfs, cgroup, intel_rdt: Support fs_context cgroup: store a reference to cgroup_ns into cgroup_fs_context cgroup1_get_tree(): separate "get cgroup_root to use" into a separate helper cgroup_do_mount(): massage calling conventions cgroup: stash cgroup_root reference into cgroup_fs_context cgroup2: switch to option-by-option parsing cgroup1: switch to option-by-option parsing cgroup: take options parsing into ->parse_monolithic() cgroup: fold cgroup1_mount() into cgroup1_get_tree() cgroup: start switching to fs_context ipc: Convert mqueue fs to fs_context proc: Add fs_context support to procfs ...
2019-03-12 14:08:19 -07:00
parent dbc2fba3fc c99c2171fc
commit 7b47a9e7c8
45 changed files with 4377 additions and 1352 deletions
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -27,6 +27,7 @@
 #include <linux/task_work.h>
 #include <linux/sched/task.h>
 #include <uapi/linux/mount.h>
+#include <linux/fs_context.h>

 #include "pnode.h"
 #include "internal.h"
@@ -940,38 +941,81 @@ static struct mount *skip_mnt_tree(struct mount *p)
 	return p;
 }

-struct vfsmount *
-vfs_kern_mount(struct file_system_type *type, int flags, const char *name, void *data)
+/**
+ * vfs_create_mount - Create a mount for a configured superblock
+ * @fc: The configuration context with the superblock attached
+ *
+ * Create a mount to an already configured superblock.  If necessary, the
+ * caller should invoke vfs_get_tree() before calling this.
+ *
+ * Note that this does not attach the mount to anything.
+ */
+struct vfsmount *vfs_create_mount(struct fs_context *fc)
 {
 	struct mount *mnt;
-	struct dentry *root;

-	if (!type)
-		return ERR_PTR(-ENODEV);
+	if (!fc->root)
+		return ERR_PTR(-EINVAL);

-	mnt = alloc_vfsmnt(name);
+	mnt = alloc_vfsmnt(fc->source ?: "none");
 	if (!mnt)
 		return ERR_PTR(-ENOMEM);

-	if (flags & SB_KERNMOUNT)
+	if (fc->sb_flags & SB_KERNMOUNT)
 		mnt->mnt.mnt_flags = MNT_INTERNAL;

-	root = mount_fs(type, flags, name, data);
-	if (IS_ERR(root)) {
-		mnt_free_id(mnt);
-		free_vfsmnt(mnt);
-		return ERR_CAST(root);
-	}
+	atomic_inc(&fc->root->d_sb->s_active);
+	mnt->mnt.mnt_sb		= fc->root->d_sb;
+	mnt->mnt.mnt_root	= dget(fc->root);
+	mnt->mnt_mountpoint	= mnt->mnt.mnt_root;
+	mnt->mnt_parent		= mnt;

-	mnt->mnt.mnt_root = root;
-	mnt->mnt.mnt_sb = root->d_sb;
-	mnt->mnt_mountpoint = mnt->mnt.mnt_root;
-	mnt->mnt_parent = mnt;
 	lock_mount_hash();
-	list_add_tail(&mnt->mnt_instance, &root->d_sb->s_mounts);
+	list_add_tail(&mnt->mnt_instance, &mnt->mnt.mnt_sb->s_mounts);
 	unlock_mount_hash();
 	return &mnt->mnt;
 }
+EXPORT_SYMBOL(vfs_create_mount);
+
+struct vfsmount *fc_mount(struct fs_context *fc)
+{
+	int err = vfs_get_tree(fc);
+	if (!err) {
+		up_write(&fc->root->d_sb->s_umount);
+		return vfs_create_mount(fc);
+	}
+	return ERR_PTR(err);
+}
+EXPORT_SYMBOL(fc_mount);
+
+struct vfsmount *vfs_kern_mount(struct file_system_type *type,
+				int flags, const char *name,
+				void *data)
+{
+	struct fs_context *fc;
+	struct vfsmount *mnt;
+	int ret = 0;
+
+	if (!type)
+		return ERR_PTR(-EINVAL);
+
+	fc = fs_context_for_mount(type, flags);
+	if (IS_ERR(fc))
+		return ERR_CAST(fc);
+
+	if (name)
+		ret = vfs_parse_fs_string(fc, "source",
+					  name, strlen(name));
+	if (!ret)
+		ret = parse_monolithic_mount_data(fc, data);
+	if (!ret)
+		mnt = fc_mount(fc);
+	else
+		mnt = ERR_PTR(ret);
+
+	put_fs_context(fc);
+	return mnt;
+}
 EXPORT_SYMBOL_GPL(vfs_kern_mount);

 struct vfsmount *
@@ -1013,27 +1057,6 @@ static struct mount *clone_mnt(struct mount *old, struct dentry *root,

 	mnt->mnt.mnt_flags = old->mnt.mnt_flags;
 	mnt->mnt.mnt_flags &= ~(MNT_WRITE_HOLD|MNT_MARKED|MNT_INTERNAL);
-	/* Don't allow unprivileged users to change mount flags */
-	if (flag & CL_UNPRIVILEGED) {
-		mnt->mnt.mnt_flags |= MNT_LOCK_ATIME;
-
-		if (mnt->mnt.mnt_flags & MNT_READONLY)
-			mnt->mnt.mnt_flags |= MNT_LOCK_READONLY;
-
-		if (mnt->mnt.mnt_flags & MNT_NODEV)
-			mnt->mnt.mnt_flags |= MNT_LOCK_NODEV;
-
-		if (mnt->mnt.mnt_flags & MNT_NOSUID)
-			mnt->mnt.mnt_flags |= MNT_LOCK_NOSUID;
-
-		if (mnt->mnt.mnt_flags & MNT_NOEXEC)
-			mnt->mnt.mnt_flags |= MNT_LOCK_NOEXEC;
-	}
-
-	/* Don't allow unprivileged users to reveal what is under a mount */
-	if ((flag & CL_UNPRIVILEGED) &&
-	    (!(flag & CL_EXPIRE) || list_empty(&old->mnt_expire)))
-		mnt->mnt.mnt_flags |= MNT_LOCKED;

 	atomic_inc(&sb->s_active);
 	mnt->mnt.mnt_sb = sb;
@@ -1464,6 +1487,29 @@ static void umount_tree(struct mount *mnt, enum umount_tree_flags how)

 static void shrink_submounts(struct mount *mnt);

+static int do_umount_root(struct super_block *sb)
+{
+	int ret = 0;
+
+	down_write(&sb->s_umount);
+	if (!sb_rdonly(sb)) {
+		struct fs_context *fc;
+
+		fc = fs_context_for_reconfigure(sb->s_root, SB_RDONLY,
+						SB_RDONLY);
+		if (IS_ERR(fc)) {
+			ret = PTR_ERR(fc);
+		} else {
+			ret = parse_monolithic_mount_data(fc, NULL);
+			if (!ret)
+				ret = reconfigure_super(fc);
+			put_fs_context(fc);
+		}
+	}
+	up_write(&sb->s_umount);
+	return ret;
+}
+
 static int do_umount(struct mount *mnt, int flags)
 {
 	struct super_block *sb = mnt->mnt.mnt_sb;
@@ -1529,11 +1575,7 @@ static int do_umount(struct mount *mnt, int flags)
 		 */
 		if (!ns_capable(sb->s_user_ns, CAP_SYS_ADMIN))
 			return -EPERM;
-		down_write(&sb->s_umount);
-		if (!sb_rdonly(sb))
-			retval = do_remount_sb(sb, SB_RDONLY, NULL, 0);
-		up_write(&sb->s_umount);
-		return retval;
+		return do_umount_root(sb);
 	}

 	namespace_lock();
@@ -1839,6 +1881,33 @@ int iterate_mounts(int (*f)(struct vfsmount *, void *), void *arg,
 	return 0;
 }

+static void lock_mnt_tree(struct mount *mnt)
+{
+	struct mount *p;
+
+	for (p = mnt; p; p = next_mnt(p, mnt)) {
+		int flags = p->mnt.mnt_flags;
+		/* Don't allow unprivileged users to change mount flags */
+		flags |= MNT_LOCK_ATIME;
+
+		if (flags & MNT_READONLY)
+			flags |= MNT_LOCK_READONLY;
+
+		if (flags & MNT_NODEV)
+			flags |= MNT_LOCK_NODEV;
+
+		if (flags & MNT_NOSUID)
+			flags |= MNT_LOCK_NOSUID;
+
+		if (flags & MNT_NOEXEC)
+			flags |= MNT_LOCK_NOEXEC;
+		/* Don't allow unprivileged users to reveal what is under a mount */
+		if (list_empty(&p->mnt_expire))
+			flags |= MNT_LOCKED;
+		p->mnt.mnt_flags = flags;
+	}
+}
+
 static void cleanup_group_ids(struct mount *mnt, struct mount *end)
 {
 	struct mount *p;
@@ -1956,6 +2025,7 @@ static int attach_recursive_mnt(struct mount *source_mnt,
 			struct mountpoint *dest_mp,
 			struct path *parent_path)
 {
+	struct user_namespace *user_ns = current->nsproxy->mnt_ns->user_ns;
 	HLIST_HEAD(tree_list);
 	struct mnt_namespace *ns = dest_mnt->mnt_ns;
 	struct mountpoint *smp;
@@ -2006,6 +2076,9 @@ static int attach_recursive_mnt(struct mount *source_mnt,
 				 child->mnt_mountpoint);
 		if (q)
 			mnt_change_mountpoint(child, smp, q);
+		/* Notice when we are propagating across user namespaces */
+		if (child->mnt_parent->mnt_ns->user_ns != user_ns)
+			lock_mnt_tree(child);
 		commit_tree(child);
 	}
 	put_mountpoint(smp);
@@ -2313,7 +2386,7 @@ static int do_remount(struct path *path, int ms_flags, int sb_flags,
 	int err;
 	struct super_block *sb = path->mnt->mnt_sb;
 	struct mount *mnt = real_mount(path->mnt);
-	void *sec_opts = NULL;
+	struct fs_context *fc;

 	if (!check_mnt(mnt))
 		return -EINVAL;
@@ -2324,24 +2397,22 @@ static int do_remount(struct path *path, int ms_flags, int sb_flags,
 	if (!can_change_locked_flags(mnt, mnt_flags))
 		return -EPERM;

-	if (data && !(sb->s_type->fs_flags & FS_BINARY_MOUNTDATA)) {
-		err = security_sb_eat_lsm_opts(data, &sec_opts);
-		if (err)
-			return err;
-	}
-	err = security_sb_remount(sb, sec_opts);
-	security_free_mnt_opts(&sec_opts);
-	if (err)
-		return err;
+	fc = fs_context_for_reconfigure(path->dentry, sb_flags, MS_RMT_MASK);
+	if (IS_ERR(fc))
+		return PTR_ERR(fc);

-	down_write(&sb->s_umount);
-	err = -EPERM;
-	if (ns_capable(sb->s_user_ns, CAP_SYS_ADMIN)) {
-		err = do_remount_sb(sb, sb_flags, data, 0);
-		if (!err)
-			set_mount_attributes(mnt, mnt_flags);
+	err = parse_monolithic_mount_data(fc, data);
+	if (!err) {
+		down_write(&sb->s_umount);
+		err = -EPERM;
+		if (ns_capable(sb->s_user_ns, CAP_SYS_ADMIN)) {
+			err = reconfigure_super(fc);
+			if (!err)
+				set_mount_attributes(mnt, mnt_flags);
+		}
+		up_write(&sb->s_umount);
 	}
-	up_write(&sb->s_umount);
+	put_fs_context(fc);
 	return err;
 }

@@ -2425,29 +2496,6 @@ out:
 	return err;
 }

-static struct vfsmount *fs_set_subtype(struct vfsmount *mnt, const char *fstype)
-{
-	int err;
-	const char *subtype = strchr(fstype, '.');
-	if (subtype) {
-		subtype++;
-		err = -EINVAL;
-		if (!subtype[0])
-			goto err;
-	} else
-		subtype = "";
-
-	mnt->mnt_sb->s_subtype = kstrdup(subtype, GFP_KERNEL);
-	err = -ENOMEM;
-	if (!mnt->mnt_sb->s_subtype)
-		goto err;
-	return mnt;
-
- err:
-	mntput(mnt);
-	return ERR_PTR(err);
-}
-
 /*
 * add a mount into a namespace's mount tree
 */
@@ -2492,7 +2540,39 @@ unlock:
 	return err;
 }

-static bool mount_too_revealing(struct vfsmount *mnt, int *new_mnt_flags);
+static bool mount_too_revealing(const struct super_block *sb, int *new_mnt_flags);
+
+/*
+ * Create a new mount using a superblock configuration and request it
+ * be added to the namespace tree.
+ */
+static int do_new_mount_fc(struct fs_context *fc, struct path *mountpoint,
+			   unsigned int mnt_flags)
+{
+	struct vfsmount *mnt;
+	struct super_block *sb = fc->root->d_sb;
+	int error;
+
+	error = security_sb_kern_mount(sb);
+	if (!error && mount_too_revealing(sb, &mnt_flags))
+		error = -EPERM;
+
+	if (unlikely(error)) {
+		fc_drop_locked(fc);
+		return error;
+	}
+
+	up_write(&sb->s_umount);
+
+	mnt = vfs_create_mount(fc);
+	if (IS_ERR(mnt))
+		return PTR_ERR(mnt);
+
+	error = do_add_mount(real_mount(mnt), mountpoint, mnt_flags);
+	if (error < 0)
+		mntput(mnt);
+	return error;
+}

 /*
 * create a new mount for userspace and request it to be added into the
@@ -2502,8 +2582,9 @@ static int do_new_mount(struct path *path, const char *fstype, int sb_flags,
 			int mnt_flags, const char *name, void *data)
 {
 	struct file_system_type *type;
-	struct vfsmount *mnt;
-	int err;
+	struct fs_context *fc;
+	const char *subtype = NULL;
+	int err = 0;

 	if (!fstype)
 		return -EINVAL;
@@ -2512,23 +2593,37 @@ static int do_new_mount(struct path *path, const char *fstype, int sb_flags,
 	if (!type)
 		return -ENODEV;

-	mnt = vfs_kern_mount(type, sb_flags, name, data);
-	if (!IS_ERR(mnt) && (type->fs_flags & FS_HAS_SUBTYPE) &&
-	    !mnt->mnt_sb->s_subtype)
-		mnt = fs_set_subtype(mnt, fstype);
-
-	put_filesystem(type);
-	if (IS_ERR(mnt))
-		return PTR_ERR(mnt);
-
-	if (mount_too_revealing(mnt, &mnt_flags)) {
-		mntput(mnt);
-		return -EPERM;
+	if (type->fs_flags & FS_HAS_SUBTYPE) {
+		subtype = strchr(fstype, '.');
+		if (subtype) {
+			subtype++;
+			if (!*subtype) {
+				put_filesystem(type);
+				return -EINVAL;
+			}
+		} else {
+			subtype = "";
+		}
 	}

-	err = do_add_mount(real_mount(mnt), path, mnt_flags);
-	if (err)
-		mntput(mnt);
+	fc = fs_context_for_mount(type, sb_flags);
+	put_filesystem(type);
+	if (IS_ERR(fc))
+		return PTR_ERR(fc);
+
+	if (subtype)
+		err = vfs_parse_fs_string(fc, "subtype",
+					  subtype, strlen(subtype));
+	if (!err && name)
+		err = vfs_parse_fs_string(fc, "source", name, strlen(name));
+	if (!err)
+		err = parse_monolithic_mount_data(fc, data);
+	if (!err)
+		err = vfs_get_tree(fc);
+	if (!err)
+		err = do_new_mount_fc(fc, path, mnt_flags);
+
+	put_fs_context(fc);
 	return err;
 }

@@ -2863,7 +2958,8 @@ static void dec_mnt_namespaces(struct ucounts *ucounts)

 static void free_mnt_ns(struct mnt_namespace *ns)
 {
-	ns_free_inum(&ns->ns);
+	if (!is_anon_ns(ns))
+		ns_free_inum(&ns->ns);
 	dec_mnt_namespaces(ns->ucounts);
 	put_user_ns(ns->user_ns);
 	kfree(ns);
@@ -2878,7 +2974,7 @@ 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;
@@ -2888,28 +2984,27 @@ 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);
 	}
-	ret = ns_alloc_inum(&new_ns->ns);
-	if (ret) {
-		kfree(new_ns);
-		dec_mnt_namespaces(ucounts);
-		return ERR_PTR(ret);
+	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;
-	new_ns->seq = atomic64_add_return(1, &mnt_ns_seq);
+	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;
 }

@@ -2933,7 +3028,7 @@ 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;

@@ -2941,13 +3036,18 @@ struct mnt_namespace *copy_mnt_ns(unsigned long flags, struct mnt_namespace *ns,
 	/* First pass: copy the tree topology */
 	copy_flags = CL_COPY_UNBINDABLE | CL_EXPIRE;
 	if (user_ns != ns->user_ns)
-		copy_flags |= CL_SHARED_TO_SLAVE | CL_UNPRIVILEGED;
+		copy_flags |= CL_SHARED_TO_SLAVE;
 	new = copy_tree(old, old->mnt.mnt_root, copy_flags);
 	if (IS_ERR(new)) {
 		namespace_unlock();
 		free_mnt_ns(new_ns);
 		return ERR_CAST(new);
 	}
+	if (user_ns != ns->user_ns) {
+		lock_mount_hash();
+		lock_mnt_tree(new);
+		unlock_mount_hash();
+	}
 	new_ns->root = new;
 	list_add_tail(&new_ns->list, &new->mnt_list);

@@ -2988,37 +3088,25 @@ 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 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 dentry *mount_subtree(struct vfsmount *m, const char *name)
 {
+	struct mount *mnt = real_mount(m);
 	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);
@@ -3228,6 +3316,7 @@ 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;
@@ -3240,10 +3329,14 @@ 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);

@@ -3297,10 +3390,10 @@ void put_mnt_ns(struct mnt_namespace *ns)
 	free_mnt_ns(ns);
 }

-struct vfsmount *kern_mount_data(struct file_system_type *type, void *data)
+struct vfsmount *kern_mount(struct file_system_type *type)
 {
 	struct vfsmount *mnt;
-	mnt = vfs_kern_mount(type, SB_KERNMOUNT, type->name, data);
+	mnt = vfs_kern_mount(type, SB_KERNMOUNT, type->name, NULL);
 	if (!IS_ERR(mnt)) {
 		/*
 		 * it is a longterm mount, don't release mnt until
@@ -3310,7 +3403,7 @@ struct vfsmount *kern_mount_data(struct file_system_type *type, void *data)
 	}
 	return mnt;
 }
-EXPORT_SYMBOL_GPL(kern_mount_data);
+EXPORT_SYMBOL_GPL(kern_mount);

 void kern_unmount(struct vfsmount *mnt)
 {
@@ -3352,7 +3445,8 @@ bool current_chrooted(void)
 	return chrooted;
 }

-static bool mnt_already_visible(struct mnt_namespace *ns, struct vfsmount *new,
+static bool mnt_already_visible(struct mnt_namespace *ns,
+				const struct super_block *sb,
 				int *new_mnt_flags)
 {
 	int new_flags = *new_mnt_flags;
@@ -3364,7 +3458,7 @@ static bool mnt_already_visible(struct mnt_namespace *ns, struct vfsmount *new,
 		struct mount *child;
 		int mnt_flags;

-		if (mnt->mnt.mnt_sb->s_type != new->mnt_sb->s_type)
+		if (mnt->mnt.mnt_sb->s_type != sb->s_type)
 			continue;

 		/* This mount is not fully visible if it's root directory
@@ -3415,7 +3509,7 @@ found:
 	return visible;
 }

-static bool mount_too_revealing(struct vfsmount *mnt, int *new_mnt_flags)
+static bool mount_too_revealing(const struct super_block *sb, int *new_mnt_flags)
 {
 	const unsigned long required_iflags = SB_I_NOEXEC | SB_I_NODEV;
 	struct mnt_namespace *ns = current->nsproxy->mnt_ns;
@@ -3425,7 +3519,7 @@ static bool mount_too_revealing(struct vfsmount *mnt, int *new_mnt_flags)
 		return false;

 	/* Can this filesystem be too revealing? */
-	s_iflags = mnt->mnt_sb->s_iflags;
+	s_iflags = sb->s_iflags;
 	if (!(s_iflags & SB_I_USERNS_VISIBLE))
 		return false;

@@ -3435,7 +3529,7 @@ static bool mount_too_revealing(struct vfsmount *mnt, int *new_mnt_flags)
 		return true;
 	}

-	return !mnt_already_visible(ns, mnt, new_mnt_flags);
+	return !mnt_already_visible(ns, sb, new_mnt_flags);
 }

 bool mnt_may_suid(struct vfsmount *mnt)
@@ -3484,6 +3578,9 @@ 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;