1 files changed, 282 insertions, 0 deletions
diff --git a/fs/nsfs.c b/fs/nsfs.c
new file mode 100644
index 000000000..30d150a4f
--- /dev/null
+++ b/fs/nsfs.c
@@ -0,0 +1,282 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/mount.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)
+{
+	struct ns_common *ns;
+	void *ret;
+
+again:
+	ns = ns_get_cb(private_data);
+	if (!ns)
+		return ERR_PTR(-ENOENT);
+
+	ret = __ns_get_path(path, ns);
+	if (IS_ERR(ret) && PTR_ERR(ret) == -EAGAIN)
+		goto again;
+	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;
+
+	while (1) {
+		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);
+		if (IS_ERR(err) && PTR_ERR(err) == -EAGAIN)
+			continue;
+		break;
+	}
+	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 struct dentry *nsfs_mount(struct file_system_type *fs_type,
+			int flags, const char *dev_name, void *data)
+{
+	return mount_pseudo(fs_type, "nsfs:", &nsfs_ops,
+			&ns_dentry_operations, NSFS_MAGIC);
+}
+static struct file_system_type nsfs = {
+	.name = "nsfs",
+	.mount = nsfs_mount,
+	.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\n");
+	nsfs_mnt->mnt_sb->s_flags &= ~SB_NOUSER;
+}