1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 *  Copyright (C) 2007
4 *
5 *  Author: Eric Biederman <ebiederm@xmision.com>
6 */
7
8#include <linux/export.h>
9#include <linux/uts.h>
10#include <linux/utsname.h>
11#include <linux/random.h>
12#include <linux/sysctl.h>
13#include <linux/wait.h>
14#include <linux/rwsem.h>
15
16#ifdef CONFIG_PROC_SYSCTL
17
18static void *get_uts(struct ctl_table *table)
19{
20	char *which = table->data;
21	struct uts_namespace *uts_ns;
22
23	uts_ns = current->nsproxy->uts_ns;
24	which = (which - (char *)&init_uts_ns) + (char *)uts_ns;
25
26	return which;
27}
28
29/*
30 *	Special case of dostring for the UTS structure. This has locks
31 *	to observe. Should this be in kernel/sys.c ????
32 */
33static int proc_do_uts_string(struct ctl_table *table, int write,
34		  void *buffer, size_t *lenp, loff_t *ppos)
35{
36	struct ctl_table uts_table;
37	int r;
38	char tmp_data[__NEW_UTS_LEN + 1];
39
40	memcpy(&uts_table, table, sizeof(uts_table));
41	uts_table.data = tmp_data;
42
43	/*
44	 * Buffer the value in tmp_data so that proc_dostring() can be called
45	 * without holding any locks.
46	 * We also need to read the original value in the write==1 case to
47	 * support partial writes.
48	 */
49	down_read(&uts_sem);
50	memcpy(tmp_data, get_uts(table), sizeof(tmp_data));
51	up_read(&uts_sem);
52	r = proc_dostring(&uts_table, write, buffer, lenp, ppos);
53
54	if (write) {
55		/*
56		 * Write back the new value.
57		 * Note that, since we dropped uts_sem, the result can
58		 * theoretically be incorrect if there are two parallel writes
59		 * at non-zero offsets to the same sysctl.
60		 */
61		add_device_randomness(tmp_data, sizeof(tmp_data));
62		down_write(&uts_sem);
63		memcpy(get_uts(table), tmp_data, sizeof(tmp_data));
64		up_write(&uts_sem);
65		proc_sys_poll_notify(table->poll);
66	}
67
68	return r;
69}
70#else
71#define proc_do_uts_string NULL
72#endif
73
74static DEFINE_CTL_TABLE_POLL(hostname_poll);
75static DEFINE_CTL_TABLE_POLL(domainname_poll);
76
77// Note: update 'enum uts_proc' to match any changes to this table
78static struct ctl_table uts_kern_table[] = {
79	{
80		.procname	= "arch",
81		.data		= init_uts_ns.name.machine,
82		.maxlen		= sizeof(init_uts_ns.name.machine),
83		.mode		= 0444,
84		.proc_handler	= proc_do_uts_string,
85	},
86	{
87		.procname	= "ostype",
88		.data		= init_uts_ns.name.sysname,
89		.maxlen		= sizeof(init_uts_ns.name.sysname),
90		.mode		= 0444,
91		.proc_handler	= proc_do_uts_string,
92	},
93	{
94		.procname	= "osrelease",
95		.data		= init_uts_ns.name.release,
96		.maxlen		= sizeof(init_uts_ns.name.release),
97		.mode		= 0444,
98		.proc_handler	= proc_do_uts_string,
99	},
100	{
101		.procname	= "version",
102		.data		= init_uts_ns.name.version,
103		.maxlen		= sizeof(init_uts_ns.name.version),
104		.mode		= 0444,
105		.proc_handler	= proc_do_uts_string,
106	},
107	{
108		.procname	= "hostname",
109		.data		= init_uts_ns.name.nodename,
110		.maxlen		= sizeof(init_uts_ns.name.nodename),
111		.mode		= 0644,
112		.proc_handler	= proc_do_uts_string,
113		.poll		= &hostname_poll,
114	},
115	{
116		.procname	= "domainname",
117		.data		= init_uts_ns.name.domainname,
118		.maxlen		= sizeof(init_uts_ns.name.domainname),
119		.mode		= 0644,
120		.proc_handler	= proc_do_uts_string,
121		.poll		= &domainname_poll,
122	},
123	{}
124};
125
126#ifdef CONFIG_PROC_SYSCTL
127/*
128 * Notify userspace about a change in a certain entry of uts_kern_table,
129 * identified by the parameter proc.
130 */
131void uts_proc_notify(enum uts_proc proc)
132{
133	struct ctl_table *table = &uts_kern_table[proc];
134
135	proc_sys_poll_notify(table->poll);
136}
137#endif
138
139static int __init utsname_sysctl_init(void)
140{
141	register_sysctl("kernel", uts_kern_table);
142	return 0;
143}
144
145device_initcall(utsname_sysctl_init);
146