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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 | #include "cred-internals.h" |
20 | |
21 | struct user_namespace init_user_ns = { |
22 | .kref = { |
23 | .refcount = ATOMIC_INIT(2), |
24 | }, |
25 | .creator = &root_user, |
26 | }; |
27 | EXPORT_SYMBOL_GPL(init_user_ns); |
28 | |
29 | /* |
30 | * UID task count cache, to get fast user lookup in "alloc_uid" |
31 | * when changing user ID's (ie setuid() and friends). |
32 | */ |
33 | |
34 | #define UIDHASH_MASK (UIDHASH_SZ - 1) |
35 | #define __uidhashfn(uid) (((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK) |
36 | #define uidhashentry(ns, uid) ((ns)->uidhash_table + __uidhashfn((uid))) |
37 | |
38 | static struct kmem_cache *uid_cachep; |
39 | |
40 | /* |
41 | * The uidhash_lock is mostly taken from process context, but it is |
42 | * occasionally also taken from softirq/tasklet context, when |
43 | * task-structs get RCU-freed. Hence all locking must be softirq-safe. |
44 | * But free_uid() is also called with local interrupts disabled, and running |
45 | * local_bh_enable() with local interrupts disabled is an error - we'll run |
46 | * softirq callbacks, and they can unconditionally enable interrupts, and |
47 | * the caller of free_uid() didn't expect that.. |
48 | */ |
49 | static DEFINE_SPINLOCK(uidhash_lock); |
50 | |
51 | /* root_user.__count is 2, 1 for init task cred, 1 for init_user_ns->creator */ |
52 | struct user_struct root_user = { |
53 | .__count = ATOMIC_INIT(2), |
54 | .processes = ATOMIC_INIT(1), |
55 | .files = ATOMIC_INIT(0), |
56 | .sigpending = ATOMIC_INIT(0), |
57 | .locked_shm = 0, |
58 | .user_ns = &init_user_ns, |
59 | }; |
60 | |
61 | /* |
62 | * These routines must be called with the uidhash spinlock held! |
63 | */ |
64 | static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent) |
65 | { |
66 | hlist_add_head(&up->uidhash_node, hashent); |
67 | } |
68 | |
69 | static void uid_hash_remove(struct user_struct *up) |
70 | { |
71 | hlist_del_init(&up->uidhash_node); |
72 | put_user_ns(up->user_ns); |
73 | } |
74 | |
75 | static struct user_struct *uid_hash_find(uid_t uid, struct hlist_head *hashent) |
76 | { |
77 | struct user_struct *user; |
78 | struct hlist_node *h; |
79 | |
80 | hlist_for_each_entry(user, h, hashent, uidhash_node) { |
81 | if (user->uid == uid) { |
82 | atomic_inc(&user->__count); |
83 | return user; |
84 | } |
85 | } |
86 | |
87 | return NULL; |
88 | } |
89 | |
90 | /* IRQs are disabled and uidhash_lock is held upon function entry. |
91 | * IRQ state (as stored in flags) is restored and uidhash_lock released |
92 | * upon function exit. |
93 | */ |
94 | static void free_user(struct user_struct *up, unsigned long flags) |
95 | { |
96 | uid_hash_remove(up); |
97 | spin_unlock_irqrestore(&uidhash_lock, flags); |
98 | key_put(up->uid_keyring); |
99 | key_put(up->session_keyring); |
100 | kmem_cache_free(uid_cachep, up); |
101 | } |
102 | |
103 | /* |
104 | * Locate the user_struct for the passed UID. If found, take a ref on it. The |
105 | * caller must undo that ref with free_uid(). |
106 | * |
107 | * If the user_struct could not be found, return NULL. |
108 | */ |
109 | struct user_struct *find_user(uid_t uid) |
110 | { |
111 | struct user_struct *ret; |
112 | unsigned long flags; |
113 | struct user_namespace *ns = current_user_ns(); |
114 | |
115 | spin_lock_irqsave(&uidhash_lock, flags); |
116 | ret = uid_hash_find(uid, uidhashentry(ns, uid)); |
117 | spin_unlock_irqrestore(&uidhash_lock, flags); |
118 | return ret; |
119 | } |
120 | |
121 | void free_uid(struct user_struct *up) |
122 | { |
123 | unsigned long flags; |
124 | |
125 | if (!up) |
126 | return; |
127 | |
128 | local_irq_save(flags); |
129 | if (atomic_dec_and_lock(&up->__count, &uidhash_lock)) |
130 | free_user(up, flags); |
131 | else |
132 | local_irq_restore(flags); |
133 | } |
134 | |
135 | struct user_struct *alloc_uid(struct user_namespace *ns, uid_t uid) |
136 | { |
137 | struct hlist_head *hashent = uidhashentry(ns, uid); |
138 | struct user_struct *up, *new; |
139 | |
140 | /* Make uid_hash_find() + uids_user_create() + uid_hash_insert() |
141 | * atomic. |
142 | */ |
143 | spin_lock_irq(&uidhash_lock); |
144 | up = uid_hash_find(uid, hashent); |
145 | spin_unlock_irq(&uidhash_lock); |
146 | |
147 | if (!up) { |
148 | new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL); |
149 | if (!new) |
150 | goto out_unlock; |
151 | |
152 | new->uid = uid; |
153 | atomic_set(&new->__count, 1); |
154 | |
155 | new->user_ns = get_user_ns(ns); |
156 | |
157 | /* |
158 | * Before adding this, check whether we raced |
159 | * on adding the same user already.. |
160 | */ |
161 | spin_lock_irq(&uidhash_lock); |
162 | up = uid_hash_find(uid, hashent); |
163 | if (up) { |
164 | /* This case is not possible when CONFIG_USER_SCHED |
165 | * is defined, since we serialize alloc_uid() using |
166 | * uids_mutex. Hence no need to call |
167 | * sched_destroy_user() or remove_user_sysfs_dir(). |
168 | */ |
169 | key_put(new->uid_keyring); |
170 | key_put(new->session_keyring); |
171 | kmem_cache_free(uid_cachep, new); |
172 | } else { |
173 | uid_hash_insert(new, hashent); |
174 | up = new; |
175 | } |
176 | spin_unlock_irq(&uidhash_lock); |
177 | } |
178 | |
179 | return up; |
180 | |
181 | put_user_ns(new->user_ns); |
182 | kmem_cache_free(uid_cachep, new); |
183 | out_unlock: |
184 | return NULL; |
185 | } |
186 | |
187 | static int __init uid_cache_init(void) |
188 | { |
189 | int n; |
190 | |
191 | uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct), |
192 | 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL); |
193 | |
194 | for(n = 0; n < UIDHASH_SZ; ++n) |
195 | INIT_HLIST_HEAD(init_user_ns.uidhash_table + n); |
196 | |
197 | /* Insert the root user immediately (init already runs as root) */ |
198 | spin_lock_irq(&uidhash_lock); |
199 | uid_hash_insert(&root_user, uidhashentry(&init_user_ns, 0)); |
200 | spin_unlock_irq(&uidhash_lock); |
201 | |
202 | return 0; |
203 | } |
204 | |
205 | module_init(uid_cache_init); |
206 |
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