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Source at commit ec7cab4cbb721bff91ec924ec691efd8daf36579 created 12 years 8 months ago. By Maarten ter Huurne, MIPS: JZ4740: A320: Updated quickstart documentation. | |
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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 | /* |
21 | * userns count is 1 for root user, 1 for init_uts_ns, |
22 | * and 1 for... ? |
23 | */ |
24 | struct user_namespace init_user_ns = { |
25 | .kref = { |
26 | .refcount = ATOMIC_INIT(3), |
27 | }, |
28 | .creator = &root_user, |
29 | }; |
30 | EXPORT_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 | |
41 | static 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 | */ |
52 | static DEFINE_SPINLOCK(uidhash_lock); |
53 | |
54 | /* root_user.__count is 2, 1 for init task cred, 1 for init_user_ns->user_ns */ |
55 | struct 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 | */ |
67 | static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent) |
68 | { |
69 | hlist_add_head(&up->uidhash_node, hashent); |
70 | } |
71 | |
72 | static 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 | |
78 | static 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 | */ |
97 | static 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 | */ |
113 | struct 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 | |
125 | void 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 | |
139 | struct 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 | |
178 | out_unlock: |
179 | return NULL; |
180 | } |
181 | |
182 | static 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 | |
200 | module_init(uid_cache_init); |
201 |
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