Line data Source code
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 : .ns.count = REFCOUNT_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 : static 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 : */
111 13 : static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent)
112 : {
113 1 : hlist_add_head(&up->uidhash_node, hashent);
114 : }
115 :
116 8 : static void uid_hash_remove(struct user_struct *up)
117 : {
118 16 : hlist_del_init(&up->uidhash_node);
119 : }
120 :
121 32 : static struct user_struct *uid_hash_find(kuid_t uid, struct hlist_head *hashent)
122 : {
123 32 : struct user_struct *user;
124 :
125 64 : hlist_for_each_entry(user, hashent, uidhash_node) {
126 8 : if (uid_eq(user->uid, uid)) {
127 8 : refcount_inc(&user->__count);
128 8 : 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 : */
139 8 : static void free_user(struct user_struct *up, unsigned long flags)
140 : __releases(&uidhash_lock)
141 : {
142 8 : uid_hash_remove(up);
143 8 : spin_unlock_irqrestore(&uidhash_lock, flags);
144 8 : kmem_cache_free(uid_cachep, up);
145 8 : }
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 : */
153 0 : struct user_struct *find_user(kuid_t uid)
154 : {
155 0 : struct user_struct *ret;
156 0 : unsigned long flags;
157 :
158 0 : spin_lock_irqsave(&uidhash_lock, flags);
159 0 : ret = uid_hash_find(uid, uidhashentry(uid));
160 0 : spin_unlock_irqrestore(&uidhash_lock, flags);
161 0 : return ret;
162 : }
163 :
164 6861 : void free_uid(struct user_struct *up)
165 : {
166 6861 : unsigned long flags;
167 :
168 6861 : if (!up)
169 0 : return;
170 :
171 6861 : if (refcount_dec_and_lock_irqsave(&up->__count, &uidhash_lock, &flags))
172 8 : free_user(up, flags);
173 : }
174 :
175 20 : struct user_struct *alloc_uid(kuid_t uid)
176 : {
177 20 : struct hlist_head *hashent = uidhashentry(uid);
178 20 : struct user_struct *up, *new;
179 :
180 20 : spin_lock_irq(&uidhash_lock);
181 20 : up = uid_hash_find(uid, hashent);
182 20 : spin_unlock_irq(&uidhash_lock);
183 :
184 20 : if (!up) {
185 12 : new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL);
186 12 : if (!new)
187 : return NULL;
188 :
189 12 : new->uid = uid;
190 12 : refcount_set(&new->__count, 1);
191 12 : ratelimit_state_init(&new->ratelimit, HZ, 100);
192 12 : 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 12 : spin_lock_irq(&uidhash_lock);
199 12 : up = uid_hash_find(uid, hashent);
200 12 : if (up) {
201 0 : kmem_cache_free(uid_cachep, new);
202 : } else {
203 12 : uid_hash_insert(new, hashent);
204 12 : up = new;
205 : }
206 12 : spin_unlock_irq(&uidhash_lock);
207 : }
208 :
209 : return up;
210 : }
211 :
212 1 : static int __init uid_cache_init(void)
213 : {
214 1 : int n;
215 :
216 1 : uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
217 : 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
218 :
219 129 : for(n = 0; n < UIDHASH_SZ; ++n)
220 128 : INIT_HLIST_HEAD(uidhash_table + n);
221 :
222 : /* Insert the root user immediately (init already runs as root) */
223 1 : spin_lock_irq(&uidhash_lock);
224 1 : uid_hash_insert(&root_user, uidhashentry(GLOBAL_ROOT_UID));
225 1 : spin_unlock_irq(&uidhash_lock);
226 :
227 1 : return 0;
228 : }
229 : subsys_initcall(uid_cache_init);
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