• Home
  • Line#
  • Scopes#
  • Navigate#
  • Raw
  • Download
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_ns.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 	.flags = USERNS_INIT_FLAGS,
55 #ifdef CONFIG_PERSISTENT_KEYRINGS
56 	.persistent_keyring_register_sem =
57 	__RWSEM_INITIALIZER(init_user_ns.persistent_keyring_register_sem),
58 #endif
59 };
60 EXPORT_SYMBOL_GPL(init_user_ns);
61 
62 /*
63  * UID task count cache, to get fast user lookup in "alloc_uid"
64  * when changing user ID's (ie setuid() and friends).
65  */
66 
67 #define UIDHASH_BITS	(CONFIG_BASE_SMALL ? 3 : 7)
68 #define UIDHASH_SZ	(1 << UIDHASH_BITS)
69 #define UIDHASH_MASK		(UIDHASH_SZ - 1)
70 #define __uidhashfn(uid)	(((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK)
71 #define uidhashentry(uid)	(uidhash_table + __uidhashfn((__kuid_val(uid))))
72 
73 static struct kmem_cache *uid_cachep;
74 struct hlist_head uidhash_table[UIDHASH_SZ];
75 
76 /*
77  * The uidhash_lock is mostly taken from process context, but it is
78  * occasionally also taken from softirq/tasklet context, when
79  * task-structs get RCU-freed. Hence all locking must be softirq-safe.
80  * But free_uid() is also called with local interrupts disabled, and running
81  * local_bh_enable() with local interrupts disabled is an error - we'll run
82  * softirq callbacks, and they can unconditionally enable interrupts, and
83  * the caller of free_uid() didn't expect that..
84  */
85 static DEFINE_SPINLOCK(uidhash_lock);
86 
87 /* root_user.__count is 1, for init task cred */
88 struct user_struct root_user = {
89 	.__count	= ATOMIC_INIT(1),
90 	.processes	= ATOMIC_INIT(1),
91 	.sigpending	= ATOMIC_INIT(0),
92 	.locked_shm     = 0,
93 	.uid		= GLOBAL_ROOT_UID,
94 };
95 
96 /*
97  * These routines must be called with the uidhash spinlock held!
98  */
uid_hash_insert(struct user_struct * up,struct hlist_head * hashent)99 static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent)
100 {
101 	hlist_add_head(&up->uidhash_node, hashent);
102 }
103 
uid_hash_remove(struct user_struct * up)104 static void uid_hash_remove(struct user_struct *up)
105 {
106 	hlist_del_init(&up->uidhash_node);
107 }
108 
uid_hash_find(kuid_t uid,struct hlist_head * hashent)109 static struct user_struct *uid_hash_find(kuid_t uid, struct hlist_head *hashent)
110 {
111 	struct user_struct *user;
112 
113 	hlist_for_each_entry(user, hashent, uidhash_node) {
114 		if (uid_eq(user->uid, uid)) {
115 			atomic_inc(&user->__count);
116 			return user;
117 		}
118 	}
119 
120 	return NULL;
121 }
122 
123 /* IRQs are disabled and uidhash_lock is held upon function entry.
124  * IRQ state (as stored in flags) is restored and uidhash_lock released
125  * upon function exit.
126  */
free_user(struct user_struct * up,unsigned long flags)127 static void free_user(struct user_struct *up, unsigned long flags)
128 	__releases(&uidhash_lock)
129 {
130 	uid_hash_remove(up);
131 	spin_unlock_irqrestore(&uidhash_lock, flags);
132 	key_put(up->uid_keyring);
133 	key_put(up->session_keyring);
134 	kmem_cache_free(uid_cachep, up);
135 }
136 
137 /*
138  * Locate the user_struct for the passed UID.  If found, take a ref on it.  The
139  * caller must undo that ref with free_uid().
140  *
141  * If the user_struct could not be found, return NULL.
142  */
find_user(kuid_t uid)143 struct user_struct *find_user(kuid_t uid)
144 {
145 	struct user_struct *ret;
146 	unsigned long flags;
147 
148 	spin_lock_irqsave(&uidhash_lock, flags);
149 	ret = uid_hash_find(uid, uidhashentry(uid));
150 	spin_unlock_irqrestore(&uidhash_lock, flags);
151 	return ret;
152 }
153 
free_uid(struct user_struct * up)154 void free_uid(struct user_struct *up)
155 {
156 	unsigned long flags;
157 
158 	if (!up)
159 		return;
160 
161 	local_irq_save(flags);
162 	if (atomic_dec_and_lock(&up->__count, &uidhash_lock))
163 		free_user(up, flags);
164 	else
165 		local_irq_restore(flags);
166 }
167 
alloc_uid(kuid_t uid)168 struct user_struct *alloc_uid(kuid_t uid)
169 {
170 	struct hlist_head *hashent = uidhashentry(uid);
171 	struct user_struct *up, *new;
172 
173 	spin_lock_irq(&uidhash_lock);
174 	up = uid_hash_find(uid, hashent);
175 	spin_unlock_irq(&uidhash_lock);
176 
177 	if (!up) {
178 		new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL);
179 		if (!new)
180 			goto out_unlock;
181 
182 		new->uid = uid;
183 		atomic_set(&new->__count, 1);
184 
185 		/*
186 		 * Before adding this, check whether we raced
187 		 * on adding the same user already..
188 		 */
189 		spin_lock_irq(&uidhash_lock);
190 		up = uid_hash_find(uid, hashent);
191 		if (up) {
192 			key_put(new->uid_keyring);
193 			key_put(new->session_keyring);
194 			kmem_cache_free(uid_cachep, new);
195 		} else {
196 			uid_hash_insert(new, hashent);
197 			up = new;
198 		}
199 		spin_unlock_irq(&uidhash_lock);
200 	}
201 
202 	return up;
203 
204 out_unlock:
205 	return NULL;
206 }
207 
uid_cache_init(void)208 static int __init uid_cache_init(void)
209 {
210 	int n;
211 
212 	uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
213 			0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
214 
215 	for(n = 0; n < UIDHASH_SZ; ++n)
216 		INIT_HLIST_HEAD(uidhash_table + n);
217 
218 	/* Insert the root user immediately (init already runs as root) */
219 	spin_lock_irq(&uidhash_lock);
220 	uid_hash_insert(&root_user, uidhashentry(GLOBAL_ROOT_UID));
221 	spin_unlock_irq(&uidhash_lock);
222 
223 	return 0;
224 }
225 subsys_initcall(uid_cache_init);
226