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 {
40 .extent[0] = {
41 .first = 0,
42 .lower_first = 0,
43 .count = 4294967295U,
44 },
45 .nr_extents = 1,
46 },
47 },
48 .gid_map = {
49 {
50 .extent[0] = {
51 .first = 0,
52 .lower_first = 0,
53 .count = 4294967295U,
54 },
55 .nr_extents = 1,
56 },
57 },
58 .projid_map = {
59 {
60 .extent[0] = {
61 .first = 0,
62 .lower_first = 0,
63 .count = 4294967295U,
64 },
65 .nr_extents = 1,
66 },
67 },
68 .ns.ns_type = ns_common_type(&init_user_ns),
69 .ns.__ns_ref = REFCOUNT_INIT(3),
70 .owner = GLOBAL_ROOT_UID,
71 .group = GLOBAL_ROOT_GID,
72 .ns.inum = ns_init_inum(&init_user_ns),
73 #ifdef CONFIG_USER_NS
74 .ns.ops = &userns_operations,
75 #endif
76 .flags = USERNS_INIT_FLAGS,
77 #ifdef CONFIG_KEYS
78 .keyring_name_list = LIST_HEAD_INIT(init_user_ns.keyring_name_list),
79 .keyring_sem = __RWSEM_INITIALIZER(init_user_ns.keyring_sem),
80 #endif
81 #if IS_ENABLED(CONFIG_BINFMT_MISC)
82 .binfmt_misc = &init_binfmt_misc,
83 #endif
84 };
85 EXPORT_SYMBOL_GPL(init_user_ns);
86
87 /*
88 * UID task count cache, to get fast user lookup in "alloc_uid"
89 * when changing user ID's (ie setuid() and friends).
90 */
91
92 #define UIDHASH_BITS (IS_ENABLED(CONFIG_BASE_SMALL) ? 3 : 7)
93 #define UIDHASH_SZ (1 << UIDHASH_BITS)
94 #define UIDHASH_MASK (UIDHASH_SZ - 1)
95 #define __uidhashfn(uid) (((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK)
96 #define uidhashentry(uid) (uidhash_table + __uidhashfn((__kuid_val(uid))))
97
98 static struct kmem_cache *uid_cachep;
99 static struct hlist_head uidhash_table[UIDHASH_SZ];
100
101 /*
102 * The uidhash_lock is mostly taken from process context, but it is
103 * occasionally also taken from softirq/tasklet context, when
104 * task-structs get RCU-freed. Hence all locking must be softirq-safe.
105 * But free_uid() is also called with local interrupts disabled, and running
106 * local_bh_enable() with local interrupts disabled is an error - we'll run
107 * softirq callbacks, and they can unconditionally enable interrupts, and
108 * the caller of free_uid() didn't expect that..
109 */
110 static DEFINE_SPINLOCK(uidhash_lock);
111
112 /* root_user.__count is 1, for init task cred */
113 struct user_struct root_user = {
114 .__count = REFCOUNT_INIT(1),
115 .uid = GLOBAL_ROOT_UID,
116 .ratelimit = RATELIMIT_STATE_INIT(root_user.ratelimit, 0, 0),
117 };
118
119 /*
120 * These routines must be called with the uidhash spinlock held!
121 */
uid_hash_insert(struct user_struct * up,struct hlist_head * hashent)122 static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent)
123 {
124 hlist_add_head(&up->uidhash_node, hashent);
125 }
126
uid_hash_remove(struct user_struct * up)127 static void uid_hash_remove(struct user_struct *up)
128 {
129 hlist_del_init(&up->uidhash_node);
130 }
131
uid_hash_find(kuid_t uid,struct hlist_head * hashent)132 static struct user_struct *uid_hash_find(kuid_t uid, struct hlist_head *hashent)
133 {
134 struct user_struct *user;
135
136 hlist_for_each_entry(user, hashent, uidhash_node) {
137 if (uid_eq(user->uid, uid)) {
138 refcount_inc(&user->__count);
139 return user;
140 }
141 }
142
143 return NULL;
144 }
145
user_epoll_alloc(struct user_struct * up)146 static int user_epoll_alloc(struct user_struct *up)
147 {
148 #ifdef CONFIG_EPOLL
149 return percpu_counter_init(&up->epoll_watches, 0, GFP_KERNEL);
150 #else
151 return 0;
152 #endif
153 }
154
user_epoll_free(struct user_struct * up)155 static void user_epoll_free(struct user_struct *up)
156 {
157 #ifdef CONFIG_EPOLL
158 percpu_counter_destroy(&up->epoll_watches);
159 #endif
160 }
161
162 /* IRQs are disabled and uidhash_lock is held upon function entry.
163 * IRQ state (as stored in flags) is restored and uidhash_lock released
164 * upon function exit.
165 */
free_user(struct user_struct * up,unsigned long flags)166 static void free_user(struct user_struct *up, unsigned long flags)
167 __releases(&uidhash_lock)
168 {
169 uid_hash_remove(up);
170 spin_unlock_irqrestore(&uidhash_lock, flags);
171 user_epoll_free(up);
172 kmem_cache_free(uid_cachep, up);
173 }
174
175 /*
176 * Locate the user_struct for the passed UID. If found, take a ref on it. The
177 * caller must undo that ref with free_uid().
178 *
179 * If the user_struct could not be found, return NULL.
180 */
find_user(kuid_t uid)181 struct user_struct *find_user(kuid_t uid)
182 {
183 struct user_struct *ret;
184 unsigned long flags;
185
186 spin_lock_irqsave(&uidhash_lock, flags);
187 ret = uid_hash_find(uid, uidhashentry(uid));
188 spin_unlock_irqrestore(&uidhash_lock, flags);
189 return ret;
190 }
191
free_uid(struct user_struct * up)192 void free_uid(struct user_struct *up)
193 {
194 unsigned long flags;
195
196 if (!up)
197 return;
198
199 if (refcount_dec_and_lock_irqsave(&up->__count, &uidhash_lock, &flags))
200 free_user(up, flags);
201 }
202 EXPORT_SYMBOL_GPL(free_uid);
203
alloc_uid(kuid_t uid)204 struct user_struct *alloc_uid(kuid_t uid)
205 {
206 struct hlist_head *hashent = uidhashentry(uid);
207 struct user_struct *up, *new;
208
209 spin_lock_irq(&uidhash_lock);
210 up = uid_hash_find(uid, hashent);
211 spin_unlock_irq(&uidhash_lock);
212
213 if (!up) {
214 new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL);
215 if (!new)
216 return NULL;
217
218 new->uid = uid;
219 refcount_set(&new->__count, 1);
220 if (user_epoll_alloc(new)) {
221 kmem_cache_free(uid_cachep, new);
222 return NULL;
223 }
224 ratelimit_state_init(&new->ratelimit, HZ, 100);
225 ratelimit_set_flags(&new->ratelimit, RATELIMIT_MSG_ON_RELEASE);
226
227 /*
228 * Before adding this, check whether we raced
229 * on adding the same user already..
230 */
231 spin_lock_irq(&uidhash_lock);
232 up = uid_hash_find(uid, hashent);
233 if (up) {
234 user_epoll_free(new);
235 kmem_cache_free(uid_cachep, new);
236 } else {
237 uid_hash_insert(new, hashent);
238 up = new;
239 }
240 spin_unlock_irq(&uidhash_lock);
241 }
242
243 return up;
244 }
245
uid_cache_init(void)246 static int __init uid_cache_init(void)
247 {
248 int n;
249
250 uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
251 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
252
253 for(n = 0; n < UIDHASH_SZ; ++n)
254 INIT_HLIST_HEAD(uidhash_table + n);
255
256 if (user_epoll_alloc(&root_user))
257 panic("root_user epoll percpu counter alloc failed");
258
259 /* Insert the root user immediately (init already runs as root) */
260 spin_lock_irq(&uidhash_lock);
261 uid_hash_insert(&root_user, uidhashentry(GLOBAL_ROOT_UID));
262 spin_unlock_irq(&uidhash_lock);
263
264 return 0;
265 }
266 subsys_initcall(uid_cache_init);
267