Line data Source code
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/interrupt.h>
17 : #include <linux/export.h>
18 : #include <linux/user_namespace.h>
19 : #include <linux/proc_ns.h>
20 :
21 : /*
22 : * userns count is 1 for root user, 1 for init_uts_ns,
23 : * and 1 for... ?
24 : */
25 : struct user_namespace init_user_ns = {
26 : .uid_map = {
27 : .nr_extents = 1,
28 : .extent[0] = {
29 : .first = 0,
30 : .lower_first = 0,
31 : .count = 4294967295U,
32 : },
33 : },
34 : .gid_map = {
35 : .nr_extents = 1,
36 : .extent[0] = {
37 : .first = 0,
38 : .lower_first = 0,
39 : .count = 4294967295U,
40 : },
41 : },
42 : .projid_map = {
43 : .nr_extents = 1,
44 : .extent[0] = {
45 : .first = 0,
46 : .lower_first = 0,
47 : .count = 4294967295U,
48 : },
49 : },
50 : .count = ATOMIC_INIT(3),
51 : .owner = GLOBAL_ROOT_UID,
52 : .group = GLOBAL_ROOT_GID,
53 : .ns.inum = PROC_USER_INIT_INO,
54 : #ifdef CONFIG_USER_NS
55 : .ns.ops = &userns_operations,
56 : #endif
57 : .flags = USERNS_INIT_FLAGS,
58 : #ifdef CONFIG_PERSISTENT_KEYRINGS
59 : .persistent_keyring_register_sem =
60 : __RWSEM_INITIALIZER(init_user_ns.persistent_keyring_register_sem),
61 : #endif
62 : };
63 : EXPORT_SYMBOL_GPL(init_user_ns);
64 :
65 : /*
66 : * UID task count cache, to get fast user lookup in "alloc_uid"
67 : * when changing user ID's (ie setuid() and friends).
68 : */
69 :
70 : #define UIDHASH_BITS (CONFIG_BASE_SMALL ? 3 : 7)
71 : #define UIDHASH_SZ (1 << UIDHASH_BITS)
72 : #define UIDHASH_MASK (UIDHASH_SZ - 1)
73 : #define __uidhashfn(uid) (((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK)
74 : #define uidhashentry(uid) (uidhash_table + __uidhashfn((__kuid_val(uid))))
75 :
76 : static struct kmem_cache *uid_cachep;
77 : struct hlist_head uidhash_table[UIDHASH_SZ];
78 :
79 : /*
80 : * The uidhash_lock is mostly taken from process context, but it is
81 : * occasionally also taken from softirq/tasklet context, when
82 : * task-structs get RCU-freed. Hence all locking must be softirq-safe.
83 : * But free_uid() is also called with local interrupts disabled, and running
84 : * local_bh_enable() with local interrupts disabled is an error - we'll run
85 : * softirq callbacks, and they can unconditionally enable interrupts, and
86 : * the caller of free_uid() didn't expect that..
87 : */
88 : static DEFINE_SPINLOCK(uidhash_lock);
89 :
90 : /* root_user.__count is 1, for init task cred */
91 : struct user_struct root_user = {
92 : .__count = ATOMIC_INIT(1),
93 : .processes = ATOMIC_INIT(1),
94 : .sigpending = ATOMIC_INIT(0),
95 : .locked_shm = 0,
96 : .uid = GLOBAL_ROOT_UID,
97 : };
98 :
99 : /*
100 : * These routines must be called with the uidhash spinlock held!
101 : */
102 : static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent)
103 : {
104 14 : hlist_add_head(&up->uidhash_node, hashent);
105 : }
106 :
107 : static void uid_hash_remove(struct user_struct *up)
108 : {
109 : hlist_del_init(&up->uidhash_node);
110 : }
111 :
112 131 : static struct user_struct *uid_hash_find(kuid_t uid, struct hlist_head *hashent)
113 : {
114 : struct user_struct *user;
115 :
116 131 : hlist_for_each_entry(user, hashent, uidhash_node) {
117 103 : if (uid_eq(user->uid, uid)) {
118 103 : atomic_inc(&user->__count);
119 103 : return user;
120 : }
121 : }
122 :
123 : return NULL;
124 : }
125 :
126 : /* IRQs are disabled and uidhash_lock is held upon function entry.
127 : * IRQ state (as stored in flags) is restored and uidhash_lock released
128 : * upon function exit.
129 : */
130 10 : static void free_user(struct user_struct *up, unsigned long flags)
131 : __releases(&uidhash_lock)
132 : {
133 : uid_hash_remove(up);
134 : spin_unlock_irqrestore(&uidhash_lock, flags);
135 10 : key_put(up->uid_keyring);
136 10 : key_put(up->session_keyring);
137 10 : kmem_cache_free(uid_cachep, up);
138 10 : }
139 :
140 : /*
141 : * Locate the user_struct for the passed UID. If found, take a ref on it. The
142 : * caller must undo that ref with free_uid().
143 : *
144 : * If the user_struct could not be found, return NULL.
145 : */
146 0 : struct user_struct *find_user(kuid_t uid)
147 : {
148 : struct user_struct *ret;
149 : unsigned long flags;
150 :
151 0 : spin_lock_irqsave(&uidhash_lock, flags);
152 0 : ret = uid_hash_find(uid, uidhashentry(uid));
153 : spin_unlock_irqrestore(&uidhash_lock, flags);
154 0 : return ret;
155 : }
156 :
157 23106 : void free_uid(struct user_struct *up)
158 : {
159 : unsigned long flags;
160 :
161 23106 : if (!up)
162 23106 : return;
163 :
164 : local_irq_save(flags);
165 23106 : if (atomic_dec_and_lock(&up->__count, &uidhash_lock))
166 10 : free_user(up, flags);
167 : else
168 23096 : local_irq_restore(flags);
169 : }
170 :
171 117 : struct user_struct *alloc_uid(kuid_t uid)
172 : {
173 117 : struct hlist_head *hashent = uidhashentry(uid);
174 : struct user_struct *up, *new;
175 :
176 : spin_lock_irq(&uidhash_lock);
177 117 : up = uid_hash_find(uid, hashent);
178 : spin_unlock_irq(&uidhash_lock);
179 :
180 117 : if (!up) {
181 14 : new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL);
182 14 : if (!new)
183 : goto out_unlock;
184 :
185 14 : new->uid = uid;
186 14 : atomic_set(&new->__count, 1);
187 :
188 : /*
189 : * Before adding this, check whether we raced
190 : * on adding the same user already..
191 : */
192 : spin_lock_irq(&uidhash_lock);
193 14 : up = uid_hash_find(uid, hashent);
194 14 : if (up) {
195 0 : key_put(new->uid_keyring);
196 0 : key_put(new->session_keyring);
197 0 : kmem_cache_free(uid_cachep, new);
198 : } else {
199 : uid_hash_insert(new, hashent);
200 : up = new;
201 : }
202 : spin_unlock_irq(&uidhash_lock);
203 : }
204 :
205 117 : return up;
206 :
207 : out_unlock:
208 : return NULL;
209 : }
210 :
211 1 : static int __init uid_cache_init(void)
212 : {
213 : int n;
214 :
215 1 : uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
216 : 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
217 :
218 129 : for(n = 0; n < UIDHASH_SZ; ++n)
219 128 : INIT_HLIST_HEAD(uidhash_table + n);
220 :
221 : /* Insert the root user immediately (init already runs as root) */
222 : spin_lock_irq(&uidhash_lock);
223 : uid_hash_insert(&root_user, uidhashentry(GLOBAL_ROOT_UID));
224 : spin_unlock_irq(&uidhash_lock);
225 :
226 1 : return 0;
227 : }
228 : subsys_initcall(uid_cache_init);
|
