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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 | __releases(&uidhash_lock) |
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 | spin_lock_irq(&uidhash_lock); |
141 | up = uid_hash_find(uid, hashent); |
142 | spin_unlock_irq(&uidhash_lock); |
143 | |
144 | if (!up) { |
145 | new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL); |
146 | if (!new) |
147 | goto out_unlock; |
148 | |
149 | new->uid = uid; |
150 | atomic_set(&new->__count, 1); |
151 | |
152 | new->user_ns = get_user_ns(ns); |
153 | |
154 | /* |
155 | * Before adding this, check whether we raced |
156 | * on adding the same user already.. |
157 | */ |
158 | spin_lock_irq(&uidhash_lock); |
159 | up = uid_hash_find(uid, hashent); |
160 | if (up) { |
161 | put_user_ns(ns); |
162 | key_put(new->uid_keyring); |
163 | key_put(new->session_keyring); |
164 | kmem_cache_free(uid_cachep, new); |
165 | } else { |
166 | uid_hash_insert(new, hashent); |
167 | up = new; |
168 | } |
169 | spin_unlock_irq(&uidhash_lock); |
170 | } |
171 | |
172 | return up; |
173 | |
174 | out_unlock: |
175 | return NULL; |
176 | } |
177 | |
178 | static int __init uid_cache_init(void) |
179 | { |
180 | int n; |
181 | |
182 | uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct), |
183 | 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL); |
184 | |
185 | for(n = 0; n < UIDHASH_SZ; ++n) |
186 | INIT_HLIST_HEAD(init_user_ns.uidhash_table + n); |
187 | |
188 | /* Insert the root user immediately (init already runs as root) */ |
189 | spin_lock_irq(&uidhash_lock); |
190 | uid_hash_insert(&root_user, uidhashentry(&init_user_ns, 0)); |
191 | spin_unlock_irq(&uidhash_lock); |
192 | |
193 | return 0; |
194 | } |
195 | |
196 | module_init(uid_cache_init); |
197 |
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