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 */
27 struct 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 };
71 EXPORT_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
84 static struct kmem_cache *uid_cachep;
85 static 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 */
96 static DEFINE_SPINLOCK(uidhash_lock);
97
98 /* root_user.__count is 1, for init task cred */
99 struct 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 */
uid_hash_insert(struct user_struct * up,struct hlist_head * hashent)108 static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent)
109 {
110 hlist_add_head(&up->uidhash_node, hashent);
111 }
112
uid_hash_remove(struct user_struct * up)113 static void uid_hash_remove(struct user_struct *up)
114 {
115 hlist_del_init(&up->uidhash_node);
116 }
117
uid_hash_find(kuid_t uid,struct hlist_head * hashent)118 static 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
user_epoll_alloc(struct user_struct * up)132 static 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
user_epoll_free(struct user_struct * up)141 static 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 */
free_user(struct user_struct * up,unsigned long flags)152 static 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 */
find_user(kuid_t uid)167 struct 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
free_uid(struct user_struct * up)178 void 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 EXPORT_SYMBOL_GPL(free_uid);
189
alloc_uid(kuid_t uid)190 struct user_struct *alloc_uid(kuid_t uid)
191 {
192 struct hlist_head *hashent = uidhashentry(uid);
193 struct user_struct *up, *new;
194
195 spin_lock_irq(&uidhash_lock);
196 up = uid_hash_find(uid, hashent);
197 spin_unlock_irq(&uidhash_lock);
198
199 if (!up) {
200 new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL);
201 if (!new)
202 return NULL;
203
204 new->uid = uid;
205 refcount_set(&new->__count, 1);
206 if (user_epoll_alloc(new)) {
207 kmem_cache_free(uid_cachep, new);
208 return NULL;
209 }
210 ratelimit_state_init(&new->ratelimit, HZ, 100);
211 ratelimit_set_flags(&new->ratelimit, RATELIMIT_MSG_ON_RELEASE);
212
213 /*
214 * Before adding this, check whether we raced
215 * on adding the same user already..
216 */
217 spin_lock_irq(&uidhash_lock);
218 up = uid_hash_find(uid, hashent);
219 if (up) {
220 user_epoll_free(new);
221 kmem_cache_free(uid_cachep, new);
222 } else {
223 uid_hash_insert(new, hashent);
224 up = new;
225 }
226 spin_unlock_irq(&uidhash_lock);
227 }
228
229 return up;
230 }
231
uid_cache_init(void)232 static int __init uid_cache_init(void)
233 {
234 int n;
235
236 uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
237 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
238
239 for(n = 0; n < UIDHASH_SZ; ++n)
240 INIT_HLIST_HEAD(uidhash_table + n);
241
242 if (user_epoll_alloc(&root_user))
243 panic("root_user epoll percpu counter alloc failed");
244
245 /* Insert the root user immediately (init already runs as root) */
246 spin_lock_irq(&uidhash_lock);
247 uid_hash_insert(&root_user, uidhashentry(GLOBAL_ROOT_UID));
248 spin_unlock_irq(&uidhash_lock);
249
250 return 0;
251 }
252 subsys_initcall(uid_cache_init);
253