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)
25 struct 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 };
30 EXPORT_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 */
37 struct user_namespace init_user_ns = {
38 .uid_map = {
39 .nr_extents = 1,
40 {
41 .extent[0] = {
42 .first = 0,
43 .lower_first = 0,
44 .count = 4294967295U,
45 },
46 },
47 },
48 .gid_map = {
49 .nr_extents = 1,
50 {
51 .extent[0] = {
52 .first = 0,
53 .lower_first = 0,
54 .count = 4294967295U,
55 },
56 },
57 },
58 .projid_map = {
59 .nr_extents = 1,
60 {
61 .extent[0] = {
62 .first = 0,
63 .lower_first = 0,
64 .count = 4294967295U,
65 },
66 },
67 },
68 .ns.count = REFCOUNT_INIT(3),
69 .owner = GLOBAL_ROOT_UID,
70 .group = GLOBAL_ROOT_GID,
71 .ns.inum = PROC_USER_INIT_INO,
72 #ifdef CONFIG_USER_NS
73 .ns.ops = &userns_operations,
74 #endif
75 .flags = USERNS_INIT_FLAGS,
76 #ifdef CONFIG_KEYS
77 .keyring_name_list = LIST_HEAD_INIT(init_user_ns.keyring_name_list),
78 .keyring_sem = __RWSEM_INITIALIZER(init_user_ns.keyring_sem),
79 #endif
80 #if IS_ENABLED(CONFIG_BINFMT_MISC)
81 .binfmt_misc = &init_binfmt_misc,
82 #endif
83 };
84 EXPORT_SYMBOL_GPL(init_user_ns);
85
86 /*
87 * UID task count cache, to get fast user lookup in "alloc_uid"
88 * when changing user ID's (ie setuid() and friends).
89 */
90
91 #define UIDHASH_BITS (IS_ENABLED(CONFIG_BASE_SMALL) ? 3 : 7)
92 #define UIDHASH_SZ (1 << UIDHASH_BITS)
93 #define UIDHASH_MASK (UIDHASH_SZ - 1)
94 #define __uidhashfn(uid) (((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK)
95 #define uidhashentry(uid) (uidhash_table + __uidhashfn((__kuid_val(uid))))
96
97 static struct kmem_cache *uid_cachep;
98 static struct hlist_head uidhash_table[UIDHASH_SZ];
99
100 /*
101 * The uidhash_lock is mostly taken from process context, but it is
102 * occasionally also taken from softirq/tasklet context, when
103 * task-structs get RCU-freed. Hence all locking must be softirq-safe.
104 * But free_uid() is also called with local interrupts disabled, and running
105 * local_bh_enable() with local interrupts disabled is an error - we'll run
106 * softirq callbacks, and they can unconditionally enable interrupts, and
107 * the caller of free_uid() didn't expect that..
108 */
109 static DEFINE_SPINLOCK(uidhash_lock);
110
111 /* root_user.__count is 1, for init task cred */
112 struct user_struct root_user = {
113 .__count = REFCOUNT_INIT(1),
114 .uid = GLOBAL_ROOT_UID,
115 .ratelimit = RATELIMIT_STATE_INIT(root_user.ratelimit, 0, 0),
116 };
117
118 /*
119 * These routines must be called with the uidhash spinlock held!
120 */
121 static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent)
122 {
123 hlist_add_head(&up->uidhash_node, hashent);
124 }
125
126 static void uid_hash_remove(struct user_struct *up)
127 {
128 hlist_del_init(&up->uidhash_node);
129 }
130
131 static struct user_struct *uid_hash_find(kuid_t uid, struct hlist_head *hashent)
132 {
133 struct user_struct *user;
134
135 hlist_for_each_entry(user, hashent, uidhash_node) {
136 if (uid_eq(user->uid, uid)) {
137 refcount_inc(&user->__count);
138 return user;
139 }
140 }
141
142 return NULL;
143 }
144
145 static int user_epoll_alloc(struct user_struct *up)
146 {
147 #ifdef CONFIG_EPOLL
148 return percpu_counter_init(&up->epoll_watches, 0, GFP_KERNEL);
149 #else
150 return 0;
151 #endif
152 }
153
154 static void user_epoll_free(struct user_struct *up)
155 {
156 #ifdef CONFIG_EPOLL
157 percpu_counter_destroy(&up->epoll_watches);
158 #endif
159 }
160
161 /* IRQs are disabled and uidhash_lock is held upon function entry.
162 * IRQ state (as stored in flags) is restored and uidhash_lock released
163 * upon function exit.
164 */
165 static void free_user(struct user_struct *up, unsigned long flags)
166 __releases(&uidhash_lock)
167 {
168 uid_hash_remove(up);
169 spin_unlock_irqrestore(&uidhash_lock, flags);
170 user_epoll_free(up);
171 kmem_cache_free(uid_cachep, up);
172 }
173
174 /*
175 * Locate the user_struct for the passed UID. If found, take a ref on it. The
176 * caller must undo that ref with free_uid().
177 *
178 * If the user_struct could not be found, return NULL.
179 */
180 struct user_struct *find_user(kuid_t uid)
181 {
182 struct user_struct *ret;
183 unsigned long flags;
184
185 spin_lock_irqsave(&uidhash_lock, flags);
186 ret = uid_hash_find(uid, uidhashentry(uid));
187 spin_unlock_irqrestore(&uidhash_lock, flags);
188 return ret;
189 }
190
191 void free_uid(struct user_struct *up)
192 {
193 unsigned long flags;
194
195 if (!up)
196 return;
197
198 if (refcount_dec_and_lock_irqsave(&up->__count, &uidhash_lock, &flags))
199 free_user(up, flags);
200 }
201 EXPORT_SYMBOL_GPL(free_uid);
202
203 struct user_struct *alloc_uid(kuid_t uid)
204 {
205 struct hlist_head *hashent = uidhashentry(uid);
206 struct user_struct *up, *new;
207
208 spin_lock_irq(&uidhash_lock);
209 up = uid_hash_find(uid, hashent);
210 spin_unlock_irq(&uidhash_lock);
211
212 if (!up) {
213 new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL);
214 if (!new)
215 return NULL;
216
217 new->uid = uid;
218 refcount_set(&new->__count, 1);
219 if (user_epoll_alloc(new)) {
220 kmem_cache_free(uid_cachep, new);
221 return NULL;
222 }
223 ratelimit_state_init(&new->ratelimit, HZ, 100);
224 ratelimit_set_flags(&new->ratelimit, RATELIMIT_MSG_ON_RELEASE);
225
226 /*
227 * Before adding this, check whether we raced
228 * on adding the same user already..
229 */
230 spin_lock_irq(&uidhash_lock);
231 up = uid_hash_find(uid, hashent);
232 if (up) {
233 user_epoll_free(new);
234 kmem_cache_free(uid_cachep, new);
235 } else {
236 uid_hash_insert(new, hashent);
237 up = new;
238 }
239 spin_unlock_irq(&uidhash_lock);
240 }
241
242 return up;
243 }
244
245 static int __init uid_cache_init(void)
246 {
247 int n;
248
249 uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
250 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
251
252 for(n = 0; n < UIDHASH_SZ; ++n)
253 INIT_HLIST_HEAD(uidhash_table + n);
254
255 if (user_epoll_alloc(&root_user))
256 panic("root_user epoll percpu counter alloc failed");
257
258 /* Insert the root user immediately (init already runs as root) */
259 spin_lock_irq(&uidhash_lock);
260 uid_hash_insert(&root_user, uidhashentry(GLOBAL_ROOT_UID));
261 spin_unlock_irq(&uidhash_lock);
262
263 return 0;
264 }
265 subsys_initcall(uid_cache_init);
266
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