1#include <linux/sched.h>
2#include <linux/namei.h>
3#include <linux/slab.h>
4#include <linux/pid_namespace.h>
5#include "internal.h"
6
7/*
8 * /proc/self:
9 */
10static int proc_self_readlink(struct dentry *dentry, char __user *buffer,
11			      int buflen)
12{
13	struct pid_namespace *ns = dentry->d_sb->s_fs_info;
14	pid_t tgid = task_tgid_nr_ns(current, ns);
15	char tmp[PROC_NUMBUF];
16	if (!tgid)
17		return -ENOENT;
18	sprintf(tmp, "%d", tgid);
19	return readlink_copy(buffer, buflen, tmp);
20}
21
22static void *proc_self_follow_link(struct dentry *dentry, struct nameidata *nd)
23{
24	struct pid_namespace *ns = dentry->d_sb->s_fs_info;
25	pid_t tgid = task_tgid_nr_ns(current, ns);
26	char *name = ERR_PTR(-ENOENT);
27	if (tgid) {
28		/* 11 for max length of signed int in decimal + NULL term */
29		name = kmalloc(12, GFP_KERNEL);
30		if (!name)
31			name = ERR_PTR(-ENOMEM);
32		else
33			sprintf(name, "%d", tgid);
34	}
35	nd_set_link(nd, name);
36	return NULL;
37}
38
39static const struct inode_operations proc_self_inode_operations = {
40	.readlink	= proc_self_readlink,
41	.follow_link	= proc_self_follow_link,
42	.put_link	= kfree_put_link,
43};
44
45static unsigned self_inum;
46
47int proc_setup_self(struct super_block *s)
48{
49	struct inode *root_inode = s->s_root->d_inode;
50	struct pid_namespace *ns = s->s_fs_info;
51	struct dentry *self;
52
53	mutex_lock(&root_inode->i_mutex);
54	self = d_alloc_name(s->s_root, "self");
55	if (self) {
56		struct inode *inode = new_inode_pseudo(s);
57		if (inode) {
58			inode->i_ino = self_inum;
59			inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
60			inode->i_mode = S_IFLNK | S_IRWXUGO;
61			inode->i_uid = GLOBAL_ROOT_UID;
62			inode->i_gid = GLOBAL_ROOT_GID;
63			inode->i_op = &proc_self_inode_operations;
64			d_add(self, inode);
65		} else {
66			dput(self);
67			self = ERR_PTR(-ENOMEM);
68		}
69	} else {
70		self = ERR_PTR(-ENOMEM);
71	}
72	mutex_unlock(&root_inode->i_mutex);
73	if (IS_ERR(self)) {
74		pr_err("proc_fill_super: can't allocate /proc/self\n");
75		return PTR_ERR(self);
76	}
77	ns->proc_self = self;
78	return 0;
79}
80
81void __init proc_self_init(void)
82{
83	proc_alloc_inum(&self_inum);
84}
85