projects/linux·blob v2.6.37-rc7 · refs

195 lines · 4.7 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/interrupt.h>
17#include <linux/module.h>
18#include <linux/user_namespace.h>
19
20struct user_namespace init_user_ns = {
21 .kref = {
22 .refcount = ATOMIC_INIT(2),
23 },
24 .creator = &root_user,
25};
26EXPORT_SYMBOL_GPL(init_user_ns);
27
28/*
29 * UID task count cache, to get fast user lookup in "alloc_uid"
30 * when changing user ID's (ie setuid() and friends).
31 */
32
33#define UIDHASH_MASK (UIDHASH_SZ - 1)
34#define __uidhashfn(uid) (((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK)
35#define uidhashentry(ns, uid) ((ns)->uidhash_table + __uidhashfn((uid)))
36
37static struct kmem_cache *uid_cachep;
38
39/*
40 * The uidhash_lock is mostly taken from process context, but it is
41 * occasionally also taken from softirq/tasklet context, when
42 * task-structs get RCU-freed. Hence all locking must be softirq-safe.
43 * But free_uid() is also called with local interrupts disabled, and running
44 * local_bh_enable() with local interrupts disabled is an error - we'll run
45 * softirq callbacks, and they can unconditionally enable interrupts, and
46 * the caller of free_uid() didn't expect that..
47 */
48static DEFINE_SPINLOCK(uidhash_lock);
49
50/* root_user.__count is 2, 1 for init task cred, 1 for init_user_ns->creator */
51struct user_struct root_user = {
52 .__count = ATOMIC_INIT(2),
53 .processes = ATOMIC_INIT(1),
54 .files = ATOMIC_INIT(0),
55 .sigpending = ATOMIC_INIT(0),
56 .locked_shm = 0,
57 .user_ns = &init_user_ns,
58};
59
60/*
61 * These routines must be called with the uidhash spinlock held!
62 */
63static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent)
64{
65 hlist_add_head(&up->uidhash_node, hashent);
66}
67
68static void uid_hash_remove(struct user_struct *up)
69{
70 hlist_del_init(&up->uidhash_node);
71 put_user_ns(up->user_ns);
72}
73
74static struct user_struct *uid_hash_find(uid_t uid, struct hlist_head *hashent)
75{
76 struct user_struct *user;
77 struct hlist_node *h;
78
79 hlist_for_each_entry(user, h, hashent, uidhash_node) {
80 if (user->uid == uid) {
81 atomic_inc(&user->__count);
82 return user;
83 }
84 }
85
86 return NULL;
87}
88
89/* IRQs are disabled and uidhash_lock is held upon function entry.
90 * IRQ state (as stored in flags) is restored and uidhash_lock released
91 * upon function exit.
92 */
93static void free_user(struct user_struct *up, unsigned long flags)
94 __releases(&uidhash_lock)
95{
96 uid_hash_remove(up);
97 spin_unlock_irqrestore(&uidhash_lock, flags);
98 key_put(up->uid_keyring);
99 key_put(up->session_keyring);
100 kmem_cache_free(uid_cachep, up);
101}
102
103/*
104 * Locate the user_struct for the passed UID. If found, take a ref on it. The
105 * caller must undo that ref with free_uid().
106 *
107 * If the user_struct could not be found, return NULL.
108 */
109struct user_struct *find_user(uid_t uid)
110{
111 struct user_struct *ret;
112 unsigned long flags;
113 struct user_namespace *ns = current_user_ns();
114
115 spin_lock_irqsave(&uidhash_lock, flags);
116 ret = uid_hash_find(uid, uidhashentry(ns, uid));
117 spin_unlock_irqrestore(&uidhash_lock, flags);
118 return ret;
119}
120
121void free_uid(struct user_struct *up)
122{
123 unsigned long flags;
124
125 if (!up)
126 return;
127
128 local_irq_save(flags);
129 if (atomic_dec_and_lock(&up->__count, &uidhash_lock))
130 free_user(up, flags);
131 else
132 local_irq_restore(flags);
133}
134
135struct user_struct *alloc_uid(struct user_namespace *ns, uid_t uid)
136{
137 struct hlist_head *hashent = uidhashentry(ns, uid);
138 struct user_struct *up, *new;
139
140 spin_lock_irq(&uidhash_lock);
141 up = uid_hash_find(uid, hashent);
142 spin_unlock_irq(&uidhash_lock);
143
144 if (!up) {
145 new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL);
146 if (!new)
147 goto out_unlock;
148
149 new->uid = uid;
150 atomic_set(&new->__count, 1);
151
152 new->user_ns = get_user_ns(ns);
153
154 /*
155 * Before adding this, check whether we raced
156 * on adding the same user already..
157 */
158 spin_lock_irq(&uidhash_lock);
159 up = uid_hash_find(uid, hashent);
160 if (up) {
161 key_put(new->uid_keyring);
162 key_put(new->session_keyring);
163 kmem_cache_free(uid_cachep, new);
164 } else {
165 uid_hash_insert(new, hashent);
166 up = new;
167 }
168 spin_unlock_irq(&uidhash_lock);
169 }
170
171 return up;
172
173out_unlock:
174 return NULL;
175}
176
177static int __init uid_cache_init(void)
178{
179 int n;
180
181 uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
182 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
183
184 for(n = 0; n < UIDHASH_SZ; ++n)
185 INIT_HLIST_HEAD(init_user_ns.uidhash_table + n);
186
187 /* Insert the root user immediately (init already runs as root) */
188 spin_lock_irq(&uidhash_lock);
189 uid_hash_insert(&root_user, uidhashentry(&init_user_ns, 0));
190 spin_unlock_irq(&uidhash_lock);
191
192 return 0;
193}
194
195module_init(uid_cache_init);