1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * The "user cache".
4 *
5 * (C) Copyright 1991-2000 Linus Torvalds
6 *
7 * We have a per-user structure to keep track of how many
8 * processes, files etc the user has claimed, in order to be
9 * able to have per-user limits for system resources.
10 */
11
12#include <linux/init.h>
13#include <linux/sched.h>
14#include <linux/slab.h>
15#include <linux/bitops.h>
16#include <linux/key.h>
17#include <linux/sched/user.h>
18#include <linux/interrupt.h>
19#include <linux/export.h>
20#include <linux/user_namespace.h>
21#include <linux/proc_ns.h>
22
23/*
24 * userns count is 1 for root user, 1 for init_uts_ns,
25 * and 1 for... ?
26 */
27struct user_namespace init_user_ns = {
28	.uid_map = {
29		.nr_extents = 1,
30		{
31			.extent[0] = {
32				.first = 0,
33				.lower_first = 0,
34				.count = 4294967295U,
35			},
36		},
37	},
38	.gid_map = {
39		.nr_extents = 1,
40		{
41			.extent[0] = {
42				.first = 0,
43				.lower_first = 0,
44				.count = 4294967295U,
45			},
46		},
47	},
48	.projid_map = {
49		.nr_extents = 1,
50		{
51			.extent[0] = {
52				.first = 0,
53				.lower_first = 0,
54				.count = 4294967295U,
55			},
56		},
57	},
58	.ns.count = REFCOUNT_INIT(3),
59	.owner = GLOBAL_ROOT_UID,
60	.group = GLOBAL_ROOT_GID,
61	.ns.inum = PROC_USER_INIT_INO,
62#ifdef CONFIG_USER_NS
63	.ns.ops = &userns_operations,
64#endif
65	.flags = USERNS_INIT_FLAGS,
66#ifdef CONFIG_KEYS
67	.keyring_name_list = LIST_HEAD_INIT(init_user_ns.keyring_name_list),
68	.keyring_sem = __RWSEM_INITIALIZER(init_user_ns.keyring_sem),
69#endif
70};
71EXPORT_SYMBOL_GPL(init_user_ns);
72
73/*
74 * UID task count cache, to get fast user lookup in "alloc_uid"
75 * when changing user ID's (ie setuid() and friends).
76 */
77
78#define UIDHASH_BITS	(CONFIG_BASE_SMALL ? 3 : 7)
79#define UIDHASH_SZ	(1 << UIDHASH_BITS)
80#define UIDHASH_MASK		(UIDHASH_SZ - 1)
81#define __uidhashfn(uid)	(((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK)
82#define uidhashentry(uid)	(uidhash_table + __uidhashfn((__kuid_val(uid))))
83
84static struct kmem_cache *uid_cachep;
85static struct hlist_head uidhash_table[UIDHASH_SZ];
86
87/*
88 * The uidhash_lock is mostly taken from process context, but it is
89 * occasionally also taken from softirq/tasklet context, when
90 * task-structs get RCU-freed. Hence all locking must be softirq-safe.
91 * But free_uid() is also called with local interrupts disabled, and running
92 * local_bh_enable() with local interrupts disabled is an error - we'll run
93 * softirq callbacks, and they can unconditionally enable interrupts, and
94 * the caller of free_uid() didn't expect that..
95 */
96static DEFINE_SPINLOCK(uidhash_lock);
97
98/* root_user.__count is 1, for init task cred */
99struct user_struct root_user = {
100	.__count	= REFCOUNT_INIT(1),
101	.uid		= GLOBAL_ROOT_UID,
102	.ratelimit	= RATELIMIT_STATE_INIT(root_user.ratelimit, 0, 0),
103};
104
105/*
106 * These routines must be called with the uidhash spinlock held!
107 */
108static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent)
109{
110	hlist_add_head(&up->uidhash_node, hashent);
111}
112
113static void uid_hash_remove(struct user_struct *up)
114{
115	hlist_del_init(&up->uidhash_node);
116}
117
118static struct user_struct *uid_hash_find(kuid_t uid, struct hlist_head *hashent)
119{
120	struct user_struct *user;
121
122	hlist_for_each_entry(user, hashent, uidhash_node) {
123		if (uid_eq(user->uid, uid)) {
124			refcount_inc(&user->__count);
125			return user;
126		}
127	}
128
129	return NULL;
130}
131
132static int user_epoll_alloc(struct user_struct *up)
133{
134#ifdef CONFIG_EPOLL
135	return percpu_counter_init(&up->epoll_watches, 0, GFP_KERNEL);
136#else
137	return 0;
138#endif
139}
140
141static void user_epoll_free(struct user_struct *up)
142{
143#ifdef CONFIG_EPOLL
144	percpu_counter_destroy(&up->epoll_watches);
145#endif
146}
147
148/* IRQs are disabled and uidhash_lock is held upon function entry.
149 * IRQ state (as stored in flags) is restored and uidhash_lock released
150 * upon function exit.
151 */
152static void free_user(struct user_struct *up, unsigned long flags)
153	__releases(&uidhash_lock)
154{
155	uid_hash_remove(up);
156	spin_unlock_irqrestore(&uidhash_lock, flags);
157	user_epoll_free(up);
158	kmem_cache_free(uid_cachep, up);
159}
160
161/*
162 * Locate the user_struct for the passed UID.  If found, take a ref on it.  The
163 * caller must undo that ref with free_uid().
164 *
165 * If the user_struct could not be found, return NULL.
166 */
167struct user_struct *find_user(kuid_t uid)
168{
169	struct user_struct *ret;
170	unsigned long flags;
171
172	spin_lock_irqsave(&uidhash_lock, flags);
173	ret = uid_hash_find(uid, uidhashentry(uid));
174	spin_unlock_irqrestore(&uidhash_lock, flags);
175	return ret;
176}
177
178void free_uid(struct user_struct *up)
179{
180	unsigned long flags;
181
182	if (!up)
183		return;
184
185	if (refcount_dec_and_lock_irqsave(&up->__count, &uidhash_lock, &flags))
186		free_user(up, flags);
187}
188
189struct user_struct *alloc_uid(kuid_t uid)
190{
191	struct hlist_head *hashent = uidhashentry(uid);
192	struct user_struct *up, *new;
193
194	spin_lock_irq(&uidhash_lock);
195	up = uid_hash_find(uid, hashent);
196	spin_unlock_irq(&uidhash_lock);
197
198	if (!up) {
199		new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL);
200		if (!new)
201			return NULL;
202
203		new->uid = uid;
204		refcount_set(&new->__count, 1);
205		if (user_epoll_alloc(new)) {
206			kmem_cache_free(uid_cachep, new);
207			return NULL;
208		}
209		ratelimit_state_init(&new->ratelimit, HZ, 100);
210		ratelimit_set_flags(&new->ratelimit, RATELIMIT_MSG_ON_RELEASE);
211
212		/*
213		 * Before adding this, check whether we raced
214		 * on adding the same user already..
215		 */
216		spin_lock_irq(&uidhash_lock);
217		up = uid_hash_find(uid, hashent);
218		if (up) {
219			user_epoll_free(new);
220			kmem_cache_free(uid_cachep, new);
221		} else {
222			uid_hash_insert(new, hashent);
223			up = new;
224		}
225		spin_unlock_irq(&uidhash_lock);
226	}
227
228	return up;
229}
230
231static int __init uid_cache_init(void)
232{
233	int n;
234
235	uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
236			0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
237
238	for(n = 0; n < UIDHASH_SZ; ++n)
239		INIT_HLIST_HEAD(uidhash_table + n);
240
241	if (user_epoll_alloc(&root_user))
242		panic("root_user epoll percpu counter alloc failed");
243
244	/* Insert the root user immediately (init already runs as root) */
245	spin_lock_irq(&uidhash_lock);
246	uid_hash_insert(&root_user, uidhashentry(GLOBAL_ROOT_UID));
247	spin_unlock_irq(&uidhash_lock);
248
249	return 0;
250}
251subsys_initcall(uid_cache_init);
252