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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/module.h> | |
18 | #include <linux/user_namespace.h> | |
19 | ||
20 | struct user_namespace init_user_ns = { | |
21 | .kref = { | |
22 | .refcount = ATOMIC_INIT(2), | |
23 | }, | |
24 | .creator = &root_user, | |
25 | }; | |
26 | EXPORT_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 | ||
37 | static 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 | */ | |
48 | static DEFINE_SPINLOCK(uidhash_lock); | |
49 | ||
50 | /* root_user.__count is 2, 1 for init task cred, 1 for init_user_ns->creator */ | |
51 | struct 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 | */ | |
63 | static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent) | |
64 | { | |
65 | hlist_add_head(&up->uidhash_node, hashent); | |
66 | } | |
67 | ||
68 | static 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 | ||
74 | static 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 | */ | |
93 | static void free_user(struct user_struct *up, unsigned long flags) | |
94 | { | |
95 | uid_hash_remove(up); | |
96 | spin_unlock_irqrestore(&uidhash_lock, flags); | |
97 | key_put(up->uid_keyring); | |
98 | key_put(up->session_keyring); | |
99 | kmem_cache_free(uid_cachep, up); | |
100 | } | |
101 | ||
102 | /* | |
103 | * Locate the user_struct for the passed UID. If found, take a ref on it. The | |
104 | * caller must undo that ref with free_uid(). | |
105 | * | |
106 | * If the user_struct could not be found, return NULL. | |
107 | */ | |
108 | struct user_struct *find_user(uid_t uid) | |
109 | { | |
110 | struct user_struct *ret; | |
111 | unsigned long flags; | |
112 | struct user_namespace *ns = current_user_ns(); | |
113 | ||
114 | spin_lock_irqsave(&uidhash_lock, flags); | |
115 | ret = uid_hash_find(uid, uidhashentry(ns, uid)); | |
116 | spin_unlock_irqrestore(&uidhash_lock, flags); | |
117 | return ret; | |
118 | } | |
119 | ||
120 | void free_uid(struct user_struct *up) | |
121 | { | |
122 | unsigned long flags; | |
123 | ||
124 | if (!up) | |
125 | return; | |
126 | ||
127 | local_irq_save(flags); | |
128 | if (atomic_dec_and_lock(&up->__count, &uidhash_lock)) | |
129 | free_user(up, flags); | |
130 | else | |
131 | local_irq_restore(flags); | |
132 | } | |
133 | ||
134 | struct user_struct *alloc_uid(struct user_namespace *ns, uid_t uid) | |
135 | { | |
136 | struct hlist_head *hashent = uidhashentry(ns, uid); | |
137 | struct user_struct *up, *new; | |
138 | ||
139 | spin_lock_irq(&uidhash_lock); | |
140 | up = uid_hash_find(uid, hashent); | |
141 | spin_unlock_irq(&uidhash_lock); | |
142 | ||
143 | if (!up) { | |
144 | new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL); | |
145 | if (!new) | |
146 | goto out_unlock; | |
147 | ||
148 | new->uid = uid; | |
149 | atomic_set(&new->__count, 1); | |
150 | ||
151 | new->user_ns = get_user_ns(ns); | |
152 | ||
153 | /* | |
154 | * Before adding this, check whether we raced | |
155 | * on adding the same user already.. | |
156 | */ | |
157 | spin_lock_irq(&uidhash_lock); | |
158 | up = uid_hash_find(uid, hashent); | |
159 | if (up) { | |
160 | key_put(new->uid_keyring); | |
161 | key_put(new->session_keyring); | |
162 | kmem_cache_free(uid_cachep, new); | |
163 | } else { | |
164 | uid_hash_insert(new, hashent); | |
165 | up = new; | |
166 | } | |
167 | spin_unlock_irq(&uidhash_lock); | |
168 | } | |
169 | ||
170 | return up; | |
171 | ||
172 | out_unlock: | |
173 | return NULL; | |
174 | } | |
175 | ||
176 | static int __init uid_cache_init(void) | |
177 | { | |
178 | int n; | |
179 | ||
180 | uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct), | |
181 | 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL); | |
182 | ||
183 | for(n = 0; n < UIDHASH_SZ; ++n) | |
184 | INIT_HLIST_HEAD(init_user_ns.uidhash_table + n); | |
185 | ||
186 | /* Insert the root user immediately (init already runs as root) */ | |
187 | spin_lock_irq(&uidhash_lock); | |
188 | uid_hash_insert(&root_user, uidhashentry(&init_user_ns, 0)); | |
189 | spin_unlock_irq(&uidhash_lock); | |
190 | ||
191 | return 0; | |
192 | } | |
193 | ||
194 | module_init(uid_cache_init); |