user.c

  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/binfmts.h>
 22#include <linux/proc_ns.h>
 23
 24#if IS_ENABLED(CONFIG_BINFMT_MISC)
 25struct binfmt_misc init_binfmt_misc = {
 26	.entries = LIST_HEAD_INIT(init_binfmt_misc.entries),
 27	.enabled = true,
 28	.entries_lock = __RW_LOCK_UNLOCKED(init_binfmt_misc.entries_lock),
 29};
 30EXPORT_SYMBOL_GPL(init_binfmt_misc);
 31#endif
 32
 33/*
 34 * userns count is 1 for root user, 1 for init_uts_ns,
 35 * and 1 for... ?
 36 */
 37struct user_namespace init_user_ns = {
 38	.ns = NS_COMMON_INIT(init_user_ns),
 39	.uid_map = {
 40		{
 41			.extent[0] = {
 42				.first = 0,
 43				.lower_first = 0,
 44				.count = 4294967295U,
 45			},
 46			.nr_extents = 1,
 47		},
 48	},
 49	.gid_map = {
 50		{
 51			.extent[0] = {
 52				.first = 0,
 53				.lower_first = 0,
 54				.count = 4294967295U,
 55			},
 56			.nr_extents = 1,
 57		},
 58	},
 59	.projid_map = {
 60		{
 61			.extent[0] = {
 62				.first = 0,
 63				.lower_first = 0,
 64				.count = 4294967295U,
 65			},
 66			.nr_extents = 1,
 67		},
 68	},
 69	.owner = GLOBAL_ROOT_UID,
 70	.group = GLOBAL_ROOT_GID,
 71	.flags = USERNS_INIT_FLAGS,
 72#ifdef CONFIG_KEYS
 73	.keyring_name_list = LIST_HEAD_INIT(init_user_ns.keyring_name_list),
 74	.keyring_sem = __RWSEM_INITIALIZER(init_user_ns.keyring_sem),
 75#endif
 76#if IS_ENABLED(CONFIG_BINFMT_MISC)
 77	.binfmt_misc = &init_binfmt_misc,
 78#endif
 79};
 80EXPORT_SYMBOL_GPL(init_user_ns);
 81
 82/*
 83 * UID task count cache, to get fast user lookup in "alloc_uid"
 84 * when changing user ID's (ie setuid() and friends).
 85 */
 86
 87#define UIDHASH_BITS	(IS_ENABLED(CONFIG_BASE_SMALL) ? 3 : 7)
 88#define UIDHASH_SZ	(1 << UIDHASH_BITS)
 89#define UIDHASH_MASK		(UIDHASH_SZ - 1)
 90#define __uidhashfn(uid)	(((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK)
 91#define uidhashentry(uid)	(uidhash_table + __uidhashfn((__kuid_val(uid))))
 92
 93static struct kmem_cache *uid_cachep;
 94static struct hlist_head uidhash_table[UIDHASH_SZ];
 95
 96/*
 97 * The uidhash_lock is mostly taken from process context, but it is
 98 * occasionally also taken from softirq/tasklet context, when
 99 * task-structs get RCU-freed. Hence all locking must be softirq-safe.
100 * But free_uid() is also called with local interrupts disabled, and running
101 * local_bh_enable() with local interrupts disabled is an error - we'll run
102 * softirq callbacks, and they can unconditionally enable interrupts, and
103 * the caller of free_uid() didn't expect that..
104 */
105static DEFINE_SPINLOCK(uidhash_lock);
106
107/* root_user.__count is 1, for init task cred */
108struct user_struct root_user = {
109	.__count	= REFCOUNT_INIT(1),
110	.uid		= GLOBAL_ROOT_UID,
111	.ratelimit	= RATELIMIT_STATE_INIT(root_user.ratelimit, 0, 0),
112};
113
114/*
115 * These routines must be called with the uidhash spinlock held!
116 */
117static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent)
118{
119	hlist_add_head(&up->uidhash_node, hashent);
120}
121
122static void uid_hash_remove(struct user_struct *up)
123{
124	hlist_del_init(&up->uidhash_node);
125}
126
127static struct user_struct *uid_hash_find(kuid_t uid, struct hlist_head *hashent)
128{
129	struct user_struct *user;
130
131	hlist_for_each_entry(user, hashent, uidhash_node) {
132		if (uid_eq(user->uid, uid)) {
133			refcount_inc(&user->__count);
134			return user;
135		}
136	}
137
138	return NULL;
139}
140
141static int user_epoll_alloc(struct user_struct *up)
142{
143#ifdef CONFIG_EPOLL
144	return percpu_counter_init(&up->epoll_watches, 0, GFP_KERNEL);
145#else
146	return 0;
147#endif
148}
149
150static void user_epoll_free(struct user_struct *up)
151{
152#ifdef CONFIG_EPOLL
153	percpu_counter_destroy(&up->epoll_watches);
154#endif
155}
156
157/* IRQs are disabled and uidhash_lock is held upon function entry.
158 * IRQ state (as stored in flags) is restored and uidhash_lock released
159 * upon function exit.
160 */
161static void free_user(struct user_struct *up, unsigned long flags)
162	__releases(&uidhash_lock)
163{
164	uid_hash_remove(up);
165	spin_unlock_irqrestore(&uidhash_lock, flags);
166	user_epoll_free(up);
167	kmem_cache_free(uid_cachep, up);
168}
169
170/*
171 * Locate the user_struct for the passed UID.  If found, take a ref on it.  The
172 * caller must undo that ref with free_uid().
173 *
174 * If the user_struct could not be found, return NULL.
175 */
176struct user_struct *find_user(kuid_t uid)
177{
178	struct user_struct *ret;
179	unsigned long flags;
180
181	spin_lock_irqsave(&uidhash_lock, flags);
182	ret = uid_hash_find(uid, uidhashentry(uid));
183	spin_unlock_irqrestore(&uidhash_lock, flags);
184	return ret;
185}
186
187void free_uid(struct user_struct *up)
188{
189	unsigned long flags;
190
191	if (!up)
192		return;
193
194	if (refcount_dec_and_lock_irqsave(&up->__count, &uidhash_lock, &flags))
195		free_user(up, flags);
196}
197EXPORT_SYMBOL_GPL(free_uid);
198
199struct user_struct *alloc_uid(kuid_t uid)
200{
201	struct hlist_head *hashent = uidhashentry(uid);
202	struct user_struct *up, *new;
203
204	spin_lock_irq(&uidhash_lock);
205	up = uid_hash_find(uid, hashent);
206	spin_unlock_irq(&uidhash_lock);
207
208	if (!up) {
209		new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL);
210		if (!new)
211			return NULL;
212
213		new->uid = uid;
214		refcount_set(&new->__count, 1);
215		if (user_epoll_alloc(new)) {
216			kmem_cache_free(uid_cachep, new);
217			return NULL;
218		}
219		ratelimit_state_init(&new->ratelimit, HZ, 100);
220		ratelimit_set_flags(&new->ratelimit, RATELIMIT_MSG_ON_RELEASE);
221
222		/*
223		 * Before adding this, check whether we raced
224		 * on adding the same user already..
225		 */
226		spin_lock_irq(&uidhash_lock);
227		up = uid_hash_find(uid, hashent);
228		if (up) {
229			user_epoll_free(new);
230			kmem_cache_free(uid_cachep, new);
231		} else {
232			uid_hash_insert(new, hashent);
233			up = new;
234		}
235		spin_unlock_irq(&uidhash_lock);
236	}
237
238	return up;
239}
240
241static int __init uid_cache_init(void)
242{
243	int n;
244
245	uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
246			0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
247
248	for(n = 0; n < UIDHASH_SZ; ++n)
249		INIT_HLIST_HEAD(uidhash_table + n);
250
251	if (user_epoll_alloc(&root_user))
252		panic("root_user epoll percpu counter alloc failed");
253
254	/* Insert the root user immediately (init already runs as root) */
255	spin_lock_irq(&uidhash_lock);
256	uid_hash_insert(&root_user, uidhashentry(GLOBAL_ROOT_UID));
257	spin_unlock_irq(&uidhash_lock);
258
259	return 0;
260}
261subsys_initcall(uid_cache_init);