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