// SPDX-License-Identifier: GPL-2.0

  #include <linux/mount.h>

  #include <linux/pseudo_fs.h>

  #include <linux/file.h>
  #include <linux/fs.h>
  #include <linux/proc_ns.h>
  #include <linux/magic.h>
  #include <linux/ktime.h>

  #include <linux/seq_file.h>

  #include <linux/user_namespace.h>
  #include <linux/nsfs.h>

  #include <linux/uaccess.h>

  
  static struct vfsmount *nsfs_mnt;

  static long ns_ioctl(struct file *filp, unsigned int ioctl,
  			unsigned long arg);

  static const struct file_operations ns_file_operations = {
  	.llseek		= no_llseek,

  	.unlocked_ioctl = ns_ioctl,

  };
  
  static char *ns_dname(struct dentry *dentry, char *buffer, int buflen)
  {

  	struct inode *inode = d_inode(dentry);

  	const struct proc_ns_operations *ns_ops = dentry->d_fsdata;
  
  	return dynamic_dname(dentry, buffer, buflen, "%s:[%lu]",
  		ns_ops->name, inode->i_ino);
  }
  
  static void ns_prune_dentry(struct dentry *dentry)
  {

  	struct inode *inode = d_inode(dentry);

  	if (inode) {
  		struct ns_common *ns = inode->i_private;
  		atomic_long_set(&ns->stashed, 0);
  	}
  }
  
  const struct dentry_operations ns_dentry_operations =
  {
  	.d_prune	= ns_prune_dentry,
  	.d_delete	= always_delete_dentry,
  	.d_dname	= ns_dname,
  };
  
  static void nsfs_evict(struct inode *inode)
  {
  	struct ns_common *ns = inode->i_private;
  	clear_inode(inode);
  	ns->ops->put(ns);
  }

  static void *__ns_get_path(struct path *path, struct ns_common *ns)

  {

  	struct vfsmount *mnt = nsfs_mnt;

  	struct dentry *dentry;
  	struct inode *inode;

  	unsigned long d;

  	rcu_read_lock();
  	d = atomic_long_read(&ns->stashed);
  	if (!d)
  		goto slow;
  	dentry = (struct dentry *)d;
  	if (!lockref_get_not_dead(&dentry->d_lockref))
  		goto slow;
  	rcu_read_unlock();

  	ns->ops->put(ns);

  got_it:

  	path->mnt = mntget(mnt);

  	path->dentry = dentry;
  	return NULL;
  slow:
  	rcu_read_unlock();
  	inode = new_inode_pseudo(mnt->mnt_sb);
  	if (!inode) {

  		ns->ops->put(ns);

  		return ERR_PTR(-ENOMEM);
  	}
  	inode->i_ino = ns->inum;

  	inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);

  	inode->i_flags |= S_IMMUTABLE;
  	inode->i_mode = S_IFREG | S_IRUGO;
  	inode->i_fop = &ns_file_operations;
  	inode->i_private = ns;

  	dentry = d_alloc_anon(mnt->mnt_sb);

  	if (!dentry) {
  		iput(inode);

  		return ERR_PTR(-ENOMEM);
  	}
  	d_instantiate(dentry, inode);

  	dentry->d_fsdata = (void *)ns->ops;

  	d = atomic_long_cmpxchg(&ns->stashed, 0, (unsigned long)dentry);
  	if (d) {
  		d_delete(dentry);	/* make sure ->d_prune() does nothing */
  		dput(dentry);
  		cpu_relax();

  		return ERR_PTR(-EAGAIN);

  	}
  	goto got_it;
  }

  void *ns_get_path_cb(struct path *path, ns_get_path_helper_t *ns_get_cb,
  		     void *private_data)

  {

  	void *ret;

  	do {
  		struct ns_common *ns = ns_get_cb(private_data);
  		if (!ns)
  			return ERR_PTR(-ENOENT);
  
  		ret = __ns_get_path(path, ns);
  	} while (ret == ERR_PTR(-EAGAIN));

  	return ret;
  }

  struct ns_get_path_task_args {
  	const struct proc_ns_operations *ns_ops;
  	struct task_struct *task;
  };
  
  static struct ns_common *ns_get_path_task(void *private_data)
  {
  	struct ns_get_path_task_args *args = private_data;
  
  	return args->ns_ops->get(args->task);
  }
  
  void *ns_get_path(struct path *path, struct task_struct *task,
  		  const struct proc_ns_operations *ns_ops)
  {
  	struct ns_get_path_task_args args = {
  		.ns_ops	= ns_ops,
  		.task	= task,
  	};
  
  	return ns_get_path_cb(path, ns_get_path_task, &args);
  }

  int open_related_ns(struct ns_common *ns,

  		   struct ns_common *(*get_ns)(struct ns_common *ns))
  {
  	struct path path = {};
  	struct file *f;
  	void *err;
  	int fd;
  
  	fd = get_unused_fd_flags(O_CLOEXEC);
  	if (fd < 0)
  		return fd;

  	do {

  		struct ns_common *relative;
  
  		relative = get_ns(ns);
  		if (IS_ERR(relative)) {
  			put_unused_fd(fd);
  			return PTR_ERR(relative);
  		}
  
  		err = __ns_get_path(&path, relative);

  	} while (err == ERR_PTR(-EAGAIN));

  	if (IS_ERR(err)) {
  		put_unused_fd(fd);
  		return PTR_ERR(err);
  	}
  
  	f = dentry_open(&path, O_RDONLY, current_cred());
  	path_put(&path);
  	if (IS_ERR(f)) {
  		put_unused_fd(fd);
  		fd = PTR_ERR(f);
  	} else
  		fd_install(fd, f);
  
  	return fd;
  }

  EXPORT_SYMBOL_GPL(open_related_ns);

  
  static long ns_ioctl(struct file *filp, unsigned int ioctl,
  			unsigned long arg)
  {

  	struct user_namespace *user_ns;

  	struct ns_common *ns = get_proc_ns(file_inode(filp));

  	uid_t __user *argp;
  	uid_t uid;

  
  	switch (ioctl) {
  	case NS_GET_USERNS:
  		return open_related_ns(ns, ns_get_owner);

  	case NS_GET_PARENT:
  		if (!ns->ops->get_parent)
  			return -EINVAL;
  		return open_related_ns(ns, ns->ops->get_parent);

  	case NS_GET_NSTYPE:
  		return ns->ops->type;

  	case NS_GET_OWNER_UID:
  		if (ns->ops->type != CLONE_NEWUSER)
  			return -EINVAL;
  		user_ns = container_of(ns, struct user_namespace, ns);
  		argp = (uid_t __user *) arg;
  		uid = from_kuid_munged(current_user_ns(), user_ns->owner);
  		return put_user(uid, argp);

  	default:
  		return -ENOTTY;
  	}
  }

  int ns_get_name(char *buf, size_t size, struct task_struct *task,
  			const struct proc_ns_operations *ns_ops)
  {
  	struct ns_common *ns;
  	int res = -ENOENT;

  	const char *name;

  	ns = ns_ops->get(task);
  	if (ns) {

  		name = ns_ops->real_ns_name ? : ns_ops->name;
  		res = snprintf(buf, size, "%s:[%u]", name, ns->inum);

  		ns_ops->put(ns);
  	}
  	return res;
  }
  
  struct file *proc_ns_fget(int fd)
  {
  	struct file *file;
  
  	file = fget(fd);
  	if (!file)
  		return ERR_PTR(-EBADF);
  
  	if (file->f_op != &ns_file_operations)
  		goto out_invalid;
  
  	return file;
  
  out_invalid:
  	fput(file);
  	return ERR_PTR(-EINVAL);
  }

  static int nsfs_show_path(struct seq_file *seq, struct dentry *dentry)
  {
  	struct inode *inode = d_inode(dentry);
  	const struct proc_ns_operations *ns_ops = dentry->d_fsdata;

  	seq_printf(seq, "%s:[%lu]", ns_ops->name, inode->i_ino);
  	return 0;

  }

  static const struct super_operations nsfs_ops = {
  	.statfs = simple_statfs,
  	.evict_inode = nsfs_evict,

  	.show_path = nsfs_show_path,

  };

  
  static int nsfs_init_fs_context(struct fs_context *fc)

  {

  	struct pseudo_fs_context *ctx = init_pseudo(fc, NSFS_MAGIC);
  	if (!ctx)
  		return -ENOMEM;
  	ctx->ops = &nsfs_ops;
  	ctx->dops = &ns_dentry_operations;
  	return 0;

  }

  static struct file_system_type nsfs = {
  	.name = "nsfs",

  	.init_fs_context = nsfs_init_fs_context,

  	.kill_sb = kill_anon_super,
  };
  
  void __init nsfs_init(void)
  {
  	nsfs_mnt = kern_mount(&nsfs);
  	if (IS_ERR(nsfs_mnt))
  		panic("can't set nsfs up
  ");

  	nsfs_mnt->mnt_sb->s_flags &= ~SB_NOUSER;

  }