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 .count = ATOMIC_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 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 .processes = ATOMIC_INIT(1),
102 .sigpending = ATOMIC_INIT(0),
103 .locked_shm = 0,
104 .uid = GLOBAL_ROOT_UID,
105 .ratelimit = RATELIMIT_STATE_INIT(root_user.ratelimit, 0, 0),
106 };
107
108 /*
109 * These routines must be called with the uidhash spinlock held!
110 */
uid_hash_insert(struct user_struct * up,struct hlist_head * hashent)111 static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent)
112 {
113 hlist_add_head(&up->uidhash_node, hashent);
114 }
115
uid_hash_remove(struct user_struct * up)116 static void uid_hash_remove(struct user_struct *up)
117 {
118 hlist_del_init(&up->uidhash_node);
119 }
120
uid_hash_find(kuid_t uid,struct hlist_head * hashent)121 static struct user_struct *uid_hash_find(kuid_t uid, struct hlist_head *hashent)
122 {
123 struct user_struct *user;
124
125 hlist_for_each_entry(user, hashent, uidhash_node) {
126 if (uid_eq(user->uid, uid)) {
127 refcount_inc(&user->__count);
128 return user;
129 }
130 }
131
132 return NULL;
133 }
134
135 /* IRQs are disabled and uidhash_lock is held upon function entry.
136 * IRQ state (as stored in flags) is restored and uidhash_lock released
137 * upon function exit.
138 */
free_user(struct user_struct * up,unsigned long flags)139 static void free_user(struct user_struct *up, unsigned long flags)
140 __releases(&uidhash_lock)
141 {
142 uid_hash_remove(up);
143 spin_unlock_irqrestore(&uidhash_lock, flags);
144 kmem_cache_free(uid_cachep, up);
145 }
146
147 /*
148 * Locate the user_struct for the passed UID. If found, take a ref on it. The
149 * caller must undo that ref with free_uid().
150 *
151 * If the user_struct could not be found, return NULL.
152 */
find_user(kuid_t uid)153 struct user_struct *find_user(kuid_t uid)
154 {
155 struct user_struct *ret;
156 unsigned long flags;
157
158 spin_lock_irqsave(&uidhash_lock, flags);
159 ret = uid_hash_find(uid, uidhashentry(uid));
160 spin_unlock_irqrestore(&uidhash_lock, flags);
161 return ret;
162 }
163
free_uid(struct user_struct * up)164 void free_uid(struct user_struct *up)
165 {
166 unsigned long flags;
167
168 if (!up)
169 return;
170
171 if (refcount_dec_and_lock_irqsave(&up->__count, &uidhash_lock, &flags))
172 free_user(up, flags);
173 }
174
alloc_uid(kuid_t uid)175 struct user_struct *alloc_uid(kuid_t uid)
176 {
177 struct hlist_head *hashent = uidhashentry(uid);
178 struct user_struct *up, *new;
179
180 spin_lock_irq(&uidhash_lock);
181 up = uid_hash_find(uid, hashent);
182 spin_unlock_irq(&uidhash_lock);
183
184 if (!up) {
185 new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL);
186 if (!new)
187 return NULL;
188
189 new->uid = uid;
190 refcount_set(&new->__count, 1);
191 ratelimit_state_init(&new->ratelimit, HZ, 100);
192 ratelimit_set_flags(&new->ratelimit, RATELIMIT_MSG_ON_RELEASE);
193
194 /*
195 * Before adding this, check whether we raced
196 * on adding the same user already..
197 */
198 spin_lock_irq(&uidhash_lock);
199 up = uid_hash_find(uid, hashent);
200 if (up) {
201 kmem_cache_free(uid_cachep, new);
202 } else {
203 uid_hash_insert(new, hashent);
204 up = new;
205 }
206 spin_unlock_irq(&uidhash_lock);
207 }
208
209 return up;
210 }
211
uid_cache_init(void)212 static int __init uid_cache_init(void)
213 {
214 int n;
215
216 uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
217 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
218
219 for(n = 0; n < UIDHASH_SZ; ++n)
220 INIT_HLIST_HEAD(uidhash_table + n);
221
222 /* Insert the root user immediately (init already runs as root) */
223 spin_lock_irq(&uidhash_lock);
224 uid_hash_insert(&root_user, uidhashentry(GLOBAL_ROOT_UID));
225 spin_unlock_irq(&uidhash_lock);
226
227 return 0;
228 }
229 subsys_initcall(uid_cache_init);
230
