1// SPDX-License-Identifier: GPL-2.0
  2#include <linux/mount.h>
  3#include <linux/file.h>
  4#include <linux/fs.h>
  5#include <linux/proc_ns.h>
  6#include <linux/magic.h>
  7#include <linux/ktime.h>
  8#include <linux/seq_file.h>
  9#include <linux/user_namespace.h>
 10#include <linux/nsfs.h>
 11#include <linux/uaccess.h>
 12
 13static struct vfsmount *nsfs_mnt;
 14
 15static long ns_ioctl(struct file *filp, unsigned int ioctl,
 16			unsigned long arg);
 17static const struct file_operations ns_file_operations = {
 18	.llseek		= no_llseek,
 19	.unlocked_ioctl = ns_ioctl,
 20};
 21
 22static char *ns_dname(struct dentry *dentry, char *buffer, int buflen)
 23{
 24	struct inode *inode = d_inode(dentry);
 25	const struct proc_ns_operations *ns_ops = dentry->d_fsdata;
 26
 27	return dynamic_dname(dentry, buffer, buflen, "%s:[%lu]",
 28		ns_ops->name, inode->i_ino);
 29}
 30
 31static void ns_prune_dentry(struct dentry *dentry)
 32{
 33	struct inode *inode = d_inode(dentry);
 34	if (inode) {
 35		struct ns_common *ns = inode->i_private;
 36		atomic_long_set(&ns->stashed, 0);
 37	}
 38}
 39
 40const struct dentry_operations ns_dentry_operations =
 41{
 42	.d_prune	= ns_prune_dentry,
 43	.d_delete	= always_delete_dentry,
 44	.d_dname	= ns_dname,
 45};
 46
 47static void nsfs_evict(struct inode *inode)
 48{
 49	struct ns_common *ns = inode->i_private;
 50	clear_inode(inode);
 51	ns->ops->put(ns);
 52}
 53
 54static void *__ns_get_path(struct path *path, struct ns_common *ns)
 55{
 56	struct vfsmount *mnt = nsfs_mnt;
 57	struct dentry *dentry;
 58	struct inode *inode;
 59	unsigned long d;
 60
 61	rcu_read_lock();
 62	d = atomic_long_read(&ns->stashed);
 63	if (!d)
 64		goto slow;
 65	dentry = (struct dentry *)d;
 66	if (!lockref_get_not_dead(&dentry->d_lockref))
 67		goto slow;
 68	rcu_read_unlock();
 69	ns->ops->put(ns);
 70got_it:
 71	path->mnt = mntget(mnt);
 72	path->dentry = dentry;
 73	return NULL;
 74slow:
 75	rcu_read_unlock();
 76	inode = new_inode_pseudo(mnt->mnt_sb);
 77	if (!inode) {
 78		ns->ops->put(ns);
 79		return ERR_PTR(-ENOMEM);
 80	}
 81	inode->i_ino = ns->inum;
 82	inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
 83	inode->i_flags |= S_IMMUTABLE;
 84	inode->i_mode = S_IFREG | S_IRUGO;
 85	inode->i_fop = &ns_file_operations;
 86	inode->i_private = ns;
 87
 88	dentry = d_alloc_pseudo(mnt->mnt_sb, &empty_name);
 89	if (!dentry) {
 90		iput(inode);
 91		return ERR_PTR(-ENOMEM);
 92	}
 93	d_instantiate(dentry, inode);
 94	dentry->d_flags |= DCACHE_RCUACCESS;
 95	dentry->d_fsdata = (void *)ns->ops;
 96	d = atomic_long_cmpxchg(&ns->stashed, 0, (unsigned long)dentry);
 97	if (d) {
 98		d_delete(dentry);	/* make sure ->d_prune() does nothing */
 99		dput(dentry);
100		cpu_relax();
101		return ERR_PTR(-EAGAIN);
102	}
103	goto got_it;
104}
105
106void *ns_get_path_cb(struct path *path, ns_get_path_helper_t *ns_get_cb,
107		     void *private_data)
108{
109	struct ns_common *ns;
110	void *ret;
111
112again:
113	ns = ns_get_cb(private_data);
114	if (!ns)
115		return ERR_PTR(-ENOENT);
116
117	ret = __ns_get_path(path, ns);
118	if (IS_ERR(ret) && PTR_ERR(ret) == -EAGAIN)
119		goto again;
120	return ret;
121}
122
123struct ns_get_path_task_args {
124	const struct proc_ns_operations *ns_ops;
125	struct task_struct *task;
126};
127
128static struct ns_common *ns_get_path_task(void *private_data)
129{
130	struct ns_get_path_task_args *args = private_data;
131
132	return args->ns_ops->get(args->task);
133}
134
135void *ns_get_path(struct path *path, struct task_struct *task,
136		  const struct proc_ns_operations *ns_ops)
137{
138	struct ns_get_path_task_args args = {
139		.ns_ops	= ns_ops,
140		.task	= task,
141	};
142
143	return ns_get_path_cb(path, ns_get_path_task, &args);
144}
145
146int open_related_ns(struct ns_common *ns,
147		   struct ns_common *(*get_ns)(struct ns_common *ns))
148{
149	struct path path = {};
150	struct file *f;
151	void *err;
152	int fd;
153
154	fd = get_unused_fd_flags(O_CLOEXEC);
155	if (fd < 0)
156		return fd;
157
158	while (1) {
159		struct ns_common *relative;
160
161		relative = get_ns(ns);
162		if (IS_ERR(relative)) {
163			put_unused_fd(fd);
164			return PTR_ERR(relative);
165		}
166
167		err = __ns_get_path(&path, relative);
168		if (IS_ERR(err) && PTR_ERR(err) == -EAGAIN)
169			continue;
170		break;
171	}
172	if (IS_ERR(err)) {
173		put_unused_fd(fd);
174		return PTR_ERR(err);
175	}
176
177	f = dentry_open(&path, O_RDONLY, current_cred());
178	path_put(&path);
179	if (IS_ERR(f)) {
180		put_unused_fd(fd);
181		fd = PTR_ERR(f);
182	} else
183		fd_install(fd, f);
184
185	return fd;
186}
187EXPORT_SYMBOL_GPL(open_related_ns);
188
189static long ns_ioctl(struct file *filp, unsigned int ioctl,
190			unsigned long arg)
191{
192	struct user_namespace *user_ns;
193	struct ns_common *ns = get_proc_ns(file_inode(filp));
194	uid_t __user *argp;
195	uid_t uid;
196
197	switch (ioctl) {
198	case NS_GET_USERNS:
199		return open_related_ns(ns, ns_get_owner);
200	case NS_GET_PARENT:
201		if (!ns->ops->get_parent)
202			return -EINVAL;
203		return open_related_ns(ns, ns->ops->get_parent);
204	case NS_GET_NSTYPE:
205		return ns->ops->type;
206	case NS_GET_OWNER_UID:
207		if (ns->ops->type != CLONE_NEWUSER)
208			return -EINVAL;
209		user_ns = container_of(ns, struct user_namespace, ns);
210		argp = (uid_t __user *) arg;
211		uid = from_kuid_munged(current_user_ns(), user_ns->owner);
212		return put_user(uid, argp);
213	default:
214		return -ENOTTY;
215	}
216}
217
218int ns_get_name(char *buf, size_t size, struct task_struct *task,
219			const struct proc_ns_operations *ns_ops)
220{
221	struct ns_common *ns;
222	int res = -ENOENT;
223	const char *name;
224	ns = ns_ops->get(task);
225	if (ns) {
226		name = ns_ops->real_ns_name ? : ns_ops->name;
227		res = snprintf(buf, size, "%s:[%u]", name, ns->inum);
228		ns_ops->put(ns);
229	}
230	return res;
231}
232
233struct file *proc_ns_fget(int fd)
234{
235	struct file *file;
236
237	file = fget(fd);
238	if (!file)
239		return ERR_PTR(-EBADF);
240
241	if (file->f_op != &ns_file_operations)
242		goto out_invalid;
243
244	return file;
245
246out_invalid:
247	fput(file);
248	return ERR_PTR(-EINVAL);
249}
250
251static int nsfs_show_path(struct seq_file *seq, struct dentry *dentry)
252{
253	struct inode *inode = d_inode(dentry);
254	const struct proc_ns_operations *ns_ops = dentry->d_fsdata;
255
256	seq_printf(seq, "%s:[%lu]", ns_ops->name, inode->i_ino);
257	return 0;
258}
259
260static const struct super_operations nsfs_ops = {
261	.statfs = simple_statfs,
262	.evict_inode = nsfs_evict,
263	.show_path = nsfs_show_path,
264};
265static struct dentry *nsfs_mount(struct file_system_type *fs_type,
266			int flags, const char *dev_name, void *data)
267{
268	return mount_pseudo(fs_type, "nsfs:", &nsfs_ops,
269			&ns_dentry_operations, NSFS_MAGIC);
270}
271static struct file_system_type nsfs = {
272	.name = "nsfs",
273	.mount = nsfs_mount,
274	.kill_sb = kill_anon_super,
275};
276
277void __init nsfs_init(void)
278{
279	nsfs_mnt = kern_mount(&nsfs);
280	if (IS_ERR(nsfs_mnt))
281		panic("can't set nsfs up\n");
282	nsfs_mnt->mnt_sb->s_flags &= ~SB_NOUSER;
283}