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_fs.h>
22 #include <linux/proc_ns.h>
23
24 /*
25 * userns count is 1 for root user, 1 for init_uts_ns,
26 * and 1 for... ?
27 */
28 struct user_namespace init_user_ns = {
29 .uid_map = {
30 .nr_extents = 1,
31 {
32 .extent[0] = {
33 .first = 0,
34 .lower_first = 0,
35 .count = 4294967295U,
36 },
37 },
38 },
39 .gid_map = {
40 .nr_extents = 1,
41 {
42 .extent[0] = {
43 .first = 0,
44 .lower_first = 0,
45 .count = 4294967295U,
46 },
47 },
48 },
49 .projid_map = {
50 .nr_extents = 1,
51 {
52 .extent[0] = {
53 .first = 0,
54 .lower_first = 0,
55 .count = 4294967295U,
56 },
57 },
58 },
59 .count = ATOMIC_INIT(3),
60 .owner = GLOBAL_ROOT_UID,
61 .group = GLOBAL_ROOT_GID,
62 .ns.inum = PROC_USER_INIT_INO,
63 #ifdef CONFIG_USER_NS
64 .ns.ops = &userns_operations,
65 #endif
66 .flags = USERNS_INIT_FLAGS,
67 #ifdef CONFIG_KEYS
68 .keyring_name_list = LIST_HEAD_INIT(init_user_ns.keyring_name_list),
69 .keyring_sem = __RWSEM_INITIALIZER(init_user_ns.keyring_sem),
70 #endif
71 };
72 EXPORT_SYMBOL_GPL(init_user_ns);
73
74 /*
75 * UID task count cache, to get fast user lookup in "alloc_uid"
76 * when changing user ID's (ie setuid() and friends).
77 */
78
79 #define UIDHASH_BITS (CONFIG_BASE_SMALL ? 3 : 7)
80 #define UIDHASH_SZ (1 << UIDHASH_BITS)
81 #define UIDHASH_MASK (UIDHASH_SZ - 1)
82 #define __uidhashfn(uid) (((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK)
83 #define uidhashentry(uid) (uidhash_table + __uidhashfn((__kuid_val(uid))))
84
85 static struct kmem_cache *uid_cachep;
86 struct hlist_head uidhash_table[UIDHASH_SZ];
87
88 /*
89 * The uidhash_lock is mostly taken from process context, but it is
90 * occasionally also taken from softirq/tasklet context, when
91 * task-structs get RCU-freed. Hence all locking must be softirq-safe.
92 * But free_uid() is also called with local interrupts disabled, and running
93 * local_bh_enable() with local interrupts disabled is an error - we'll run
94 * softirq callbacks, and they can unconditionally enable interrupts, and
95 * the caller of free_uid() didn't expect that..
96 */
97 static DEFINE_SPINLOCK(uidhash_lock);
98
99 /* root_user.__count is 1, for init task cred */
100 struct user_struct root_user = {
101 .__count = REFCOUNT_INIT(1),
102 .processes = ATOMIC_INIT(1),
103 .sigpending = ATOMIC_INIT(0),
104 .locked_shm = 0,
105 .uid = GLOBAL_ROOT_UID,
106 .ratelimit = RATELIMIT_STATE_INIT(root_user.ratelimit, 0, 0),
107 };
108
109 /*
110 * These routines must be called with the uidhash spinlock held!
111 */
uid_hash_insert(struct user_struct * up,struct hlist_head * hashent)112 static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent)
113 {
114 hlist_add_head(&up->uidhash_node, hashent);
115 }
116
uid_hash_remove(struct user_struct * up)117 static void uid_hash_remove(struct user_struct *up)
118 {
119 hlist_del_init(&up->uidhash_node);
120 }
121
uid_hash_find(kuid_t uid,struct hlist_head * hashent)122 static struct user_struct *uid_hash_find(kuid_t uid, struct hlist_head *hashent)
123 {
124 struct user_struct *user;
125
126 hlist_for_each_entry(user, hashent, uidhash_node) {
127 if (uid_eq(user->uid, uid)) {
128 refcount_inc(&user->__count);
129 return user;
130 }
131 }
132
133 return NULL;
134 }
135
136 /* IRQs are disabled and uidhash_lock is held upon function entry.
137 * IRQ state (as stored in flags) is restored and uidhash_lock released
138 * upon function exit.
139 */
free_user(struct user_struct * up,unsigned long flags)140 static void free_user(struct user_struct *up, unsigned long flags)
141 __releases(&uidhash_lock)
142 {
143 uid_hash_remove(up);
144 spin_unlock_irqrestore(&uidhash_lock, flags);
145 kmem_cache_free(uid_cachep, up);
146 }
147
148 /*
149 * Locate the user_struct for the passed UID. If found, take a ref on it. The
150 * caller must undo that ref with free_uid().
151 *
152 * If the user_struct could not be found, return NULL.
153 */
find_user(kuid_t uid)154 struct user_struct *find_user(kuid_t uid)
155 {
156 struct user_struct *ret;
157 unsigned long flags;
158
159 spin_lock_irqsave(&uidhash_lock, flags);
160 ret = uid_hash_find(uid, uidhashentry(uid));
161 spin_unlock_irqrestore(&uidhash_lock, flags);
162 return ret;
163 }
164
free_uid(struct user_struct * up)165 void free_uid(struct user_struct *up)
166 {
167 unsigned long flags;
168
169 if (!up)
170 return;
171
172 if (refcount_dec_and_lock_irqsave(&up->__count, &uidhash_lock, &flags))
173 free_user(up, flags);
174 }
175
alloc_uid(kuid_t uid)176 struct user_struct *alloc_uid(kuid_t uid)
177 {
178 struct hlist_head *hashent = uidhashentry(uid);
179 struct user_struct *up, *new;
180
181 spin_lock_irq(&uidhash_lock);
182 up = uid_hash_find(uid, hashent);
183 spin_unlock_irq(&uidhash_lock);
184
185 if (!up) {
186 new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL);
187 if (!new)
188 return NULL;
189
190 new->uid = uid;
191 refcount_set(&new->__count, 1);
192 ratelimit_state_init(&new->ratelimit, HZ, 100);
193 ratelimit_set_flags(&new->ratelimit, RATELIMIT_MSG_ON_RELEASE);
194
195 /*
196 * Before adding this, check whether we raced
197 * on adding the same user already..
198 */
199 spin_lock_irq(&uidhash_lock);
200 up = uid_hash_find(uid, hashent);
201 if (up) {
202 kmem_cache_free(uid_cachep, new);
203 } else {
204 uid_hash_insert(new, hashent);
205 up = new;
206 }
207 spin_unlock_irq(&uidhash_lock);
208 }
209 proc_register_uid(uid);
210
211 return up;
212 }
213
uid_cache_init(void)214 static int __init uid_cache_init(void)
215 {
216 int n;
217
218 uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
219 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
220
221 for(n = 0; n < UIDHASH_SZ; ++n)
222 INIT_HLIST_HEAD(uidhash_table + n);
223
224 /* Insert the root user immediately (init already runs as root) */
225 spin_lock_irq(&uidhash_lock);
226 uid_hash_insert(&root_user, uidhashentry(GLOBAL_ROOT_UID));
227 spin_unlock_irq(&uidhash_lock);
228 proc_register_uid(GLOBAL_ROOT_UID);
229
230 return 0;
231 }
232 subsys_initcall(uid_cache_init);
233