Loading...
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
20/*
21 * userns count is 1 for root user, 1 for init_uts_ns,
22 * and 1 for... ?
23 */
24struct user_namespace init_user_ns = {
25 .uid_map = {
26 .nr_extents = 1,
27 .extent[0] = {
28 .first = 0,
29 .lower_first = 0,
30 .count = 4294967295U,
31 },
32 },
33 .gid_map = {
34 .nr_extents = 1,
35 .extent[0] = {
36 .first = 0,
37 .lower_first = 0,
38 .count = 4294967295U,
39 },
40 },
41 .kref = {
42 .refcount = ATOMIC_INIT(3),
43 },
44 .owner = GLOBAL_ROOT_UID,
45 .group = GLOBAL_ROOT_GID,
46};
47EXPORT_SYMBOL_GPL(init_user_ns);
48
49/*
50 * UID task count cache, to get fast user lookup in "alloc_uid"
51 * when changing user ID's (ie setuid() and friends).
52 */
53
54#define UIDHASH_BITS (CONFIG_BASE_SMALL ? 3 : 7)
55#define UIDHASH_SZ (1 << UIDHASH_BITS)
56#define UIDHASH_MASK (UIDHASH_SZ - 1)
57#define __uidhashfn(uid) (((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK)
58#define uidhashentry(uid) (uidhash_table + __uidhashfn((__kuid_val(uid))))
59
60static struct kmem_cache *uid_cachep;
61struct hlist_head uidhash_table[UIDHASH_SZ];
62
63/*
64 * The uidhash_lock is mostly taken from process context, but it is
65 * occasionally also taken from softirq/tasklet context, when
66 * task-structs get RCU-freed. Hence all locking must be softirq-safe.
67 * But free_uid() is also called with local interrupts disabled, and running
68 * local_bh_enable() with local interrupts disabled is an error - we'll run
69 * softirq callbacks, and they can unconditionally enable interrupts, and
70 * the caller of free_uid() didn't expect that..
71 */
72static DEFINE_SPINLOCK(uidhash_lock);
73
74/* root_user.__count is 1, for init task cred */
75struct user_struct root_user = {
76 .__count = ATOMIC_INIT(1),
77 .processes = ATOMIC_INIT(1),
78 .files = ATOMIC_INIT(0),
79 .sigpending = ATOMIC_INIT(0),
80 .locked_shm = 0,
81 .uid = GLOBAL_ROOT_UID,
82};
83
84/*
85 * These routines must be called with the uidhash spinlock held!
86 */
87static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent)
88{
89 hlist_add_head(&up->uidhash_node, hashent);
90}
91
92static void uid_hash_remove(struct user_struct *up)
93{
94 hlist_del_init(&up->uidhash_node);
95}
96
97static struct user_struct *uid_hash_find(kuid_t uid, struct hlist_head *hashent)
98{
99 struct user_struct *user;
100 struct hlist_node *h;
101
102 hlist_for_each_entry(user, h, hashent, uidhash_node) {
103 if (uid_eq(user->uid, uid)) {
104 atomic_inc(&user->__count);
105 return user;
106 }
107 }
108
109 return NULL;
110}
111
112/* IRQs are disabled and uidhash_lock is held upon function entry.
113 * IRQ state (as stored in flags) is restored and uidhash_lock released
114 * upon function exit.
115 */
116static void free_user(struct user_struct *up, unsigned long flags)
117 __releases(&uidhash_lock)
118{
119 uid_hash_remove(up);
120 spin_unlock_irqrestore(&uidhash_lock, flags);
121 key_put(up->uid_keyring);
122 key_put(up->session_keyring);
123 kmem_cache_free(uid_cachep, up);
124}
125
126/*
127 * Locate the user_struct for the passed UID. If found, take a ref on it. The
128 * caller must undo that ref with free_uid().
129 *
130 * If the user_struct could not be found, return NULL.
131 */
132struct user_struct *find_user(kuid_t uid)
133{
134 struct user_struct *ret;
135 unsigned long flags;
136
137 spin_lock_irqsave(&uidhash_lock, flags);
138 ret = uid_hash_find(uid, uidhashentry(uid));
139 spin_unlock_irqrestore(&uidhash_lock, flags);
140 return ret;
141}
142
143void free_uid(struct user_struct *up)
144{
145 unsigned long flags;
146
147 if (!up)
148 return;
149
150 local_irq_save(flags);
151 if (atomic_dec_and_lock(&up->__count, &uidhash_lock))
152 free_user(up, flags);
153 else
154 local_irq_restore(flags);
155}
156
157struct user_struct *alloc_uid(kuid_t uid)
158{
159 struct hlist_head *hashent = uidhashentry(uid);
160 struct user_struct *up, *new;
161
162 spin_lock_irq(&uidhash_lock);
163 up = uid_hash_find(uid, hashent);
164 spin_unlock_irq(&uidhash_lock);
165
166 if (!up) {
167 new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL);
168 if (!new)
169 goto out_unlock;
170
171 new->uid = uid;
172 atomic_set(&new->__count, 1);
173
174 /*
175 * Before adding this, check whether we raced
176 * on adding the same user already..
177 */
178 spin_lock_irq(&uidhash_lock);
179 up = uid_hash_find(uid, hashent);
180 if (up) {
181 key_put(new->uid_keyring);
182 key_put(new->session_keyring);
183 kmem_cache_free(uid_cachep, new);
184 } else {
185 uid_hash_insert(new, hashent);
186 up = new;
187 }
188 spin_unlock_irq(&uidhash_lock);
189 }
190
191 return up;
192
193out_unlock:
194 return NULL;
195}
196
197static int __init uid_cache_init(void)
198{
199 int n;
200
201 uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
202 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
203
204 for(n = 0; n < UIDHASH_SZ; ++n)
205 INIT_HLIST_HEAD(uidhash_table + n);
206
207 /* Insert the root user immediately (init already runs as root) */
208 spin_lock_irq(&uidhash_lock);
209 uid_hash_insert(&root_user, uidhashentry(GLOBAL_ROOT_UID));
210 spin_unlock_irq(&uidhash_lock);
211
212 return 0;
213}
214
215module_init(uid_cache_init);
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
20/*
21 * userns count is 1 for root user, 1 for init_uts_ns,
22 * and 1 for... ?
23 */
24struct user_namespace init_user_ns = {
25 .kref = {
26 .refcount = ATOMIC_INIT(3),
27 },
28 .creator = &root_user,
29};
30EXPORT_SYMBOL_GPL(init_user_ns);
31
32/*
33 * UID task count cache, to get fast user lookup in "alloc_uid"
34 * when changing user ID's (ie setuid() and friends).
35 */
36
37#define UIDHASH_MASK (UIDHASH_SZ - 1)
38#define __uidhashfn(uid) (((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK)
39#define uidhashentry(ns, uid) ((ns)->uidhash_table + __uidhashfn((uid)))
40
41static struct kmem_cache *uid_cachep;
42
43/*
44 * The uidhash_lock is mostly taken from process context, but it is
45 * occasionally also taken from softirq/tasklet context, when
46 * task-structs get RCU-freed. Hence all locking must be softirq-safe.
47 * But free_uid() is also called with local interrupts disabled, and running
48 * local_bh_enable() with local interrupts disabled is an error - we'll run
49 * softirq callbacks, and they can unconditionally enable interrupts, and
50 * the caller of free_uid() didn't expect that..
51 */
52static DEFINE_SPINLOCK(uidhash_lock);
53
54/* root_user.__count is 2, 1 for init task cred, 1 for init_user_ns->user_ns */
55struct user_struct root_user = {
56 .__count = ATOMIC_INIT(2),
57 .processes = ATOMIC_INIT(1),
58 .files = ATOMIC_INIT(0),
59 .sigpending = ATOMIC_INIT(0),
60 .locked_shm = 0,
61 .user_ns = &init_user_ns,
62};
63
64/*
65 * These routines must be called with the uidhash spinlock held!
66 */
67static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent)
68{
69 hlist_add_head(&up->uidhash_node, hashent);
70}
71
72static void uid_hash_remove(struct user_struct *up)
73{
74 hlist_del_init(&up->uidhash_node);
75 put_user_ns(up->user_ns);
76}
77
78static struct user_struct *uid_hash_find(uid_t uid, struct hlist_head *hashent)
79{
80 struct user_struct *user;
81 struct hlist_node *h;
82
83 hlist_for_each_entry(user, h, hashent, uidhash_node) {
84 if (user->uid == uid) {
85 atomic_inc(&user->__count);
86 return user;
87 }
88 }
89
90 return NULL;
91}
92
93/* IRQs are disabled and uidhash_lock is held upon function entry.
94 * IRQ state (as stored in flags) is restored and uidhash_lock released
95 * upon function exit.
96 */
97static void free_user(struct user_struct *up, unsigned long flags)
98 __releases(&uidhash_lock)
99{
100 uid_hash_remove(up);
101 spin_unlock_irqrestore(&uidhash_lock, flags);
102 key_put(up->uid_keyring);
103 key_put(up->session_keyring);
104 kmem_cache_free(uid_cachep, up);
105}
106
107/*
108 * Locate the user_struct for the passed UID. If found, take a ref on it. The
109 * caller must undo that ref with free_uid().
110 *
111 * If the user_struct could not be found, return NULL.
112 */
113struct user_struct *find_user(uid_t uid)
114{
115 struct user_struct *ret;
116 unsigned long flags;
117 struct user_namespace *ns = current_user_ns();
118
119 spin_lock_irqsave(&uidhash_lock, flags);
120 ret = uid_hash_find(uid, uidhashentry(ns, uid));
121 spin_unlock_irqrestore(&uidhash_lock, flags);
122 return ret;
123}
124
125void free_uid(struct user_struct *up)
126{
127 unsigned long flags;
128
129 if (!up)
130 return;
131
132 local_irq_save(flags);
133 if (atomic_dec_and_lock(&up->__count, &uidhash_lock))
134 free_user(up, flags);
135 else
136 local_irq_restore(flags);
137}
138
139struct user_struct *alloc_uid(struct user_namespace *ns, uid_t uid)
140{
141 struct hlist_head *hashent = uidhashentry(ns, uid);
142 struct user_struct *up, *new;
143
144 spin_lock_irq(&uidhash_lock);
145 up = uid_hash_find(uid, hashent);
146 spin_unlock_irq(&uidhash_lock);
147
148 if (!up) {
149 new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL);
150 if (!new)
151 goto out_unlock;
152
153 new->uid = uid;
154 atomic_set(&new->__count, 1);
155
156 new->user_ns = get_user_ns(ns);
157
158 /*
159 * Before adding this, check whether we raced
160 * on adding the same user already..
161 */
162 spin_lock_irq(&uidhash_lock);
163 up = uid_hash_find(uid, hashent);
164 if (up) {
165 put_user_ns(ns);
166 key_put(new->uid_keyring);
167 key_put(new->session_keyring);
168 kmem_cache_free(uid_cachep, new);
169 } else {
170 uid_hash_insert(new, hashent);
171 up = new;
172 }
173 spin_unlock_irq(&uidhash_lock);
174 }
175
176 return up;
177
178out_unlock:
179 return NULL;
180}
181
182static int __init uid_cache_init(void)
183{
184 int n;
185
186 uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
187 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
188
189 for(n = 0; n < UIDHASH_SZ; ++n)
190 INIT_HLIST_HEAD(init_user_ns.uidhash_table + n);
191
192 /* Insert the root user immediately (init already runs as root) */
193 spin_lock_irq(&uidhash_lock);
194 uid_hash_insert(&root_user, uidhashentry(&init_user_ns, 0));
195 spin_unlock_irq(&uidhash_lock);
196
197 return 0;
198}
199
200module_init(uid_cache_init);