projects/linux·blob v4.12 · refs

229 lines · 5.4 KiB

1/*
2 * The "user cache".
3 *
4 * (C) Copyright 1991-2000 Linus Torvalds
5 *
6 * We have a per-user structure to keep track of how many
7 * processes, files etc the user has claimed, in order to be
8 * able to have per-user limits for system resources.
9 */
10
11#include <linux/init.h>
12#include <linux/sched.h>
13#include <linux/slab.h>
14#include <linux/bitops.h>
15#include <linux/key.h>
16#include <linux/sched/user.h>
17#include <linux/interrupt.h>
18#include <linux/export.h>
19#include <linux/user_namespace.h>
20#include <linux/proc_ns.h>
21
22/*
23 * userns count is 1 for root user, 1 for init_uts_ns,
24 * and 1 for... ?
25 */
26struct user_namespace init_user_ns = {
27 .uid_map = {
28 .nr_extents = 1,
29 .extent[0] = {
30 .first = 0,
31 .lower_first = 0,
32 .count = 4294967295U,
33 },
34 },
35 .gid_map = {
36 .nr_extents = 1,
37 .extent[0] = {
38 .first = 0,
39 .lower_first = 0,
40 .count = 4294967295U,
41 },
42 },
43 .projid_map = {
44 .nr_extents = 1,
45 .extent[0] = {
46 .first = 0,
47 .lower_first = 0,
48 .count = 4294967295U,
49 },
50 },
51 .count = ATOMIC_INIT(3),
52 .owner = GLOBAL_ROOT_UID,
53 .group = GLOBAL_ROOT_GID,
54 .ns.inum = PROC_USER_INIT_INO,
55#ifdef CONFIG_USER_NS
56 .ns.ops = &userns_operations,
57#endif
58 .flags = USERNS_INIT_FLAGS,
59#ifdef CONFIG_PERSISTENT_KEYRINGS
60 .persistent_keyring_register_sem =
61 __RWSEM_INITIALIZER(init_user_ns.persistent_keyring_register_sem),
62#endif
63};
64EXPORT_SYMBOL_GPL(init_user_ns);
65
66/*
67 * UID task count cache, to get fast user lookup in "alloc_uid"
68 * when changing user ID's (ie setuid() and friends).
69 */
70
71#define UIDHASH_BITS (CONFIG_BASE_SMALL ? 3 : 7)
72#define UIDHASH_SZ (1 << UIDHASH_BITS)
73#define UIDHASH_MASK (UIDHASH_SZ - 1)
74#define __uidhashfn(uid) (((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK)
75#define uidhashentry(uid) (uidhash_table + __uidhashfn((__kuid_val(uid))))
76
77static struct kmem_cache *uid_cachep;
78struct hlist_head uidhash_table[UIDHASH_SZ];
79
80/*
81 * The uidhash_lock is mostly taken from process context, but it is
82 * occasionally also taken from softirq/tasklet context, when
83 * task-structs get RCU-freed. Hence all locking must be softirq-safe.
84 * But free_uid() is also called with local interrupts disabled, and running
85 * local_bh_enable() with local interrupts disabled is an error - we'll run
86 * softirq callbacks, and they can unconditionally enable interrupts, and
87 * the caller of free_uid() didn't expect that..
88 */
89static DEFINE_SPINLOCK(uidhash_lock);
90
91/* root_user.__count is 1, for init task cred */
92struct user_struct root_user = {
93 .__count = ATOMIC_INIT(1),
94 .processes = ATOMIC_INIT(1),
95 .sigpending = ATOMIC_INIT(0),
96 .locked_shm = 0,
97 .uid = GLOBAL_ROOT_UID,
98};
99
100/*
101 * These routines must be called with the uidhash spinlock held!
102 */
103static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent)
104{
105 hlist_add_head(&up->uidhash_node, hashent);
106}
107
108static void uid_hash_remove(struct user_struct *up)
109{
110 hlist_del_init(&up->uidhash_node);
111}
112
113static struct user_struct *uid_hash_find(kuid_t uid, struct hlist_head *hashent)
114{
115 struct user_struct *user;
116
117 hlist_for_each_entry(user, hashent, uidhash_node) {
118 if (uid_eq(user->uid, uid)) {
119 atomic_inc(&user->__count);
120 return user;
121 }
122 }
123
124 return NULL;
125}
126
127/* IRQs are disabled and uidhash_lock is held upon function entry.
128 * IRQ state (as stored in flags) is restored and uidhash_lock released
129 * upon function exit.
130 */
131static void free_user(struct user_struct *up, unsigned long flags)
132 __releases(&uidhash_lock)
133{
134 uid_hash_remove(up);
135 spin_unlock_irqrestore(&uidhash_lock, flags);
136 key_put(up->uid_keyring);
137 key_put(up->session_keyring);
138 kmem_cache_free(uid_cachep, up);
139}
140
141/*
142 * Locate the user_struct for the passed UID. If found, take a ref on it. The
143 * caller must undo that ref with free_uid().
144 *
145 * If the user_struct could not be found, return NULL.
146 */
147struct user_struct *find_user(kuid_t uid)
148{
149 struct user_struct *ret;
150 unsigned long flags;
151
152 spin_lock_irqsave(&uidhash_lock, flags);
153 ret = uid_hash_find(uid, uidhashentry(uid));
154 spin_unlock_irqrestore(&uidhash_lock, flags);
155 return ret;
156}
157
158void free_uid(struct user_struct *up)
159{
160 unsigned long flags;
161
162 if (!up)
163 return;
164
165 local_irq_save(flags);
166 if (atomic_dec_and_lock(&up->__count, &uidhash_lock))
167 free_user(up, flags);
168 else
169 local_irq_restore(flags);
170}
171
172struct user_struct *alloc_uid(kuid_t uid)
173{
174 struct hlist_head *hashent = uidhashentry(uid);
175 struct user_struct *up, *new;
176
177 spin_lock_irq(&uidhash_lock);
178 up = uid_hash_find(uid, hashent);
179 spin_unlock_irq(&uidhash_lock);
180
181 if (!up) {
182 new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL);
183 if (!new)
184 goto out_unlock;
185
186 new->uid = uid;
187 atomic_set(&new->__count, 1);
188
189 /*
190 * Before adding this, check whether we raced
191 * on adding the same user already..
192 */
193 spin_lock_irq(&uidhash_lock);
194 up = uid_hash_find(uid, hashent);
195 if (up) {
196 key_put(new->uid_keyring);
197 key_put(new->session_keyring);
198 kmem_cache_free(uid_cachep, new);
199 } else {
200 uid_hash_insert(new, hashent);
201 up = new;
202 }
203 spin_unlock_irq(&uidhash_lock);
204 }
205
206 return up;
207
208out_unlock:
209 return NULL;
210}
211
212static 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}
229subsys_initcall(uid_cache_init);