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