projects/linux·blob v7.3-rc2 · refs

261 lines · 6.2 KiB

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 = HLIST_HEAD_INIT,
27 .enabled = true,
28 .entries_lock = __SPIN_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);