self.c

 1// SPDX-License-Identifier: GPL-2.0
 2#include <linux/cache.h>
 3#include <linux/sched.h>
 4#include <linux/slab.h>
 5#include <linux/pid_namespace.h>
 6#include "internal.h"
 7
 8/*
 9 * /proc/self:
10 */
11static const char *proc_self_get_link(struct dentry *dentry,
12				      struct inode *inode,
13				      struct delayed_call *done)
14{
15	struct pid_namespace *ns = proc_pid_ns(inode->i_sb);
16	pid_t tgid = task_tgid_nr_ns(current, ns);
17	char *name;
18
19	if (!tgid)
20		return ERR_PTR(-ENOENT);
21	/* max length of unsigned int in decimal + NULL term */
22	name = kmalloc(10 + 1, dentry ? GFP_KERNEL : GFP_ATOMIC);
23	if (unlikely(!name))
24		return dentry ? ERR_PTR(-ENOMEM) : ERR_PTR(-ECHILD);
25	sprintf(name, "%u", tgid);
26	set_delayed_call(done, kfree_link, name);
27	return name;
28}
29
30static const struct inode_operations proc_self_inode_operations = {
31	.get_link	= proc_self_get_link,
32};
33
34unsigned self_inum __ro_after_init;
35
36int proc_setup_self(struct super_block *s)
37{
38	struct inode *root_inode = d_inode(s->s_root);
39	struct dentry *self;
40	int ret = -ENOMEM;
41
42	inode_lock(root_inode);
43	self = d_alloc_name(s->s_root, "self");
44	if (self) {
45		struct inode *inode = new_inode(s);
46		if (inode) {
47			inode->i_ino = self_inum;
48			simple_inode_init_ts(inode);
49			inode->i_mode = S_IFLNK | S_IRWXUGO;
50			inode->i_uid = GLOBAL_ROOT_UID;
51			inode->i_gid = GLOBAL_ROOT_GID;
52			inode->i_op = &proc_self_inode_operations;
53			d_make_persistent(self, inode);
54			ret = 0;
55		}
56		dput(self);
57	}
58	inode_unlock(root_inode);
59
60	if (ret)
61		pr_err("proc_fill_super: can't allocate /proc/self\n");
62
63	return ret;
64}
65
66void __init proc_self_init(void)
67{
68	proc_alloc_inum(&self_inum);
69}