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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 | */ | |
26 | struct 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 | }; | |
64 | EXPORT_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 | ||
77 | static struct kmem_cache *uid_cachep; | |
78 | struct 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 | */ | |
89 | static DEFINE_SPINLOCK(uidhash_lock); | |
90 | ||
91 | /* root_user.__count is 1, for init task cred */ | |
92 | struct 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 | */ | |
103 | static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent) | |
104 | { | |
105 | hlist_add_head(&up->uidhash_node, hashent); | |
106 | } | |
107 | ||
108 | static void uid_hash_remove(struct user_struct *up) | |
109 | { | |
110 | hlist_del_init(&up->uidhash_node); | |
111 | } | |
112 | ||
113 | static 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 | */ | |
131 | static 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 | */ | |
147 | struct 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 | ||
158 | void 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 | ||
172 | struct 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 | ||
208 | out_unlock: | |
209 | return NULL; | |
210 | } | |
211 | ||
212 | static 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 | } | |
229 | subsys_initcall(uid_cache_init); |