1#include <linux/mount.h>
  2#include <linux/file.h>
  3#include <linux/fs.h>
  4#include <linux/proc_ns.h>
  5#include <linux/magic.h>
  6#include <linux/ktime.h>
  7#include <linux/seq_file.h>
  8
  9static struct vfsmount *nsfs_mnt;
 10
 11static const struct file_operations ns_file_operations = {
 12	.llseek		= no_llseek,
 13};
 14
 15static char *ns_dname(struct dentry *dentry, char *buffer, int buflen)
 16{
 17	struct inode *inode = d_inode(dentry);
 18	const struct proc_ns_operations *ns_ops = dentry->d_fsdata;
 19
 20	return dynamic_dname(dentry, buffer, buflen, "%s:[%lu]",
 21		ns_ops->name, inode->i_ino);
 22}
 23
 24static void ns_prune_dentry(struct dentry *dentry)
 25{
 26	struct inode *inode = d_inode(dentry);
 27	if (inode) {
 28		struct ns_common *ns = inode->i_private;
 29		atomic_long_set(&ns->stashed, 0);
 30	}
 31}
 32
 33const struct dentry_operations ns_dentry_operations =
 34{
 35	.d_prune	= ns_prune_dentry,
 36	.d_delete	= always_delete_dentry,
 37	.d_dname	= ns_dname,
 38};
 39
 40static void nsfs_evict(struct inode *inode)
 41{
 42	struct ns_common *ns = inode->i_private;
 43	clear_inode(inode);
 44	ns->ops->put(ns);
 45}
 46
 47void *ns_get_path(struct path *path, struct task_struct *task,
 48			const struct proc_ns_operations *ns_ops)
 49{
 50	struct vfsmount *mnt = mntget(nsfs_mnt);
 51	struct qstr qname = { .name = "", };
 52	struct dentry *dentry;
 53	struct inode *inode;
 54	struct ns_common *ns;
 55	unsigned long d;
 56
 57again:
 58	ns = ns_ops->get(task);
 59	if (!ns) {
 60		mntput(mnt);
 61		return ERR_PTR(-ENOENT);
 62	}
 63	rcu_read_lock();
 64	d = atomic_long_read(&ns->stashed);
 65	if (!d)
 66		goto slow;
 67	dentry = (struct dentry *)d;
 68	if (!lockref_get_not_dead(&dentry->d_lockref))
 69		goto slow;
 70	rcu_read_unlock();
 71	ns_ops->put(ns);
 72got_it:
 73	path->mnt = mnt;
 74	path->dentry = dentry;
 75	return NULL;
 76slow:
 77	rcu_read_unlock();
 78	inode = new_inode_pseudo(mnt->mnt_sb);
 79	if (!inode) {
 80		ns_ops->put(ns);
 81		mntput(mnt);
 82		return ERR_PTR(-ENOMEM);
 83	}
 84	inode->i_ino = ns->inum;
 85	inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
 86	inode->i_flags |= S_IMMUTABLE;
 87	inode->i_mode = S_IFREG | S_IRUGO;
 88	inode->i_fop = &ns_file_operations;
 89	inode->i_private = ns;
 90
 91	dentry = d_alloc_pseudo(mnt->mnt_sb, &qname);
 92	if (!dentry) {
 93		iput(inode);
 94		mntput(mnt);
 95		return ERR_PTR(-ENOMEM);
 96	}
 97	d_instantiate(dentry, inode);
 98	dentry->d_fsdata = (void *)ns_ops;
 99	d = atomic_long_cmpxchg(&ns->stashed, 0, (unsigned long)dentry);
100	if (d) {
101		d_delete(dentry);	/* make sure ->d_prune() does nothing */
102		dput(dentry);
103		cpu_relax();
104		goto again;
105	}
106	goto got_it;
107}
108
109int ns_get_name(char *buf, size_t size, struct task_struct *task,
110			const struct proc_ns_operations *ns_ops)
111{
112	struct ns_common *ns;
113	int res = -ENOENT;
114	ns = ns_ops->get(task);
115	if (ns) {
116		res = snprintf(buf, size, "%s:[%u]", ns_ops->name, ns->inum);
117		ns_ops->put(ns);
118	}
119	return res;
120}
121
122struct file *proc_ns_fget(int fd)
123{
124	struct file *file;
125
126	file = fget(fd);
127	if (!file)
128		return ERR_PTR(-EBADF);
129
130	if (file->f_op != &ns_file_operations)
131		goto out_invalid;
132
133	return file;
134
135out_invalid:
136	fput(file);
137	return ERR_PTR(-EINVAL);
138}
139
140static int nsfs_show_path(struct seq_file *seq, struct dentry *dentry)
141{
142	struct inode *inode = d_inode(dentry);
143	const struct proc_ns_operations *ns_ops = dentry->d_fsdata;
144
145	seq_printf(seq, "%s:[%lu]", ns_ops->name, inode->i_ino);
146	return 0;
147}
148
149static const struct super_operations nsfs_ops = {
150	.statfs = simple_statfs,
151	.evict_inode = nsfs_evict,
152	.show_path = nsfs_show_path,
153};
154static struct dentry *nsfs_mount(struct file_system_type *fs_type,
155			int flags, const char *dev_name, void *data)
156{
157	return mount_pseudo(fs_type, "nsfs:", &nsfs_ops,
158			&ns_dentry_operations, NSFS_MAGIC);
159}
160static struct file_system_type nsfs = {
161	.name = "nsfs",
162	.mount = nsfs_mount,
163	.kill_sb = kill_anon_super,
164};
165
166void __init nsfs_init(void)
167{
168	nsfs_mnt = kern_mount(&nsfs);
169	if (IS_ERR(nsfs_mnt))
170		panic("can't set nsfs up\n");
171	nsfs_mnt->mnt_sb->s_flags &= ~MS_NOUSER;
172}