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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/export.h>
18 #include <linux/user_namespace.h>
19 #include <linux/proc_fs.h>
20 #include <linux/proc_ns.h>
21 
22 /*
23  * userns count is 1 for root user, 1 for init_uts_ns,
24  * and 1 for... ?
25  */
26 struct user_namespace init_user_ns = {
27 	.uid_map = {
28 		.nr_extents = 1,
29 		.extent[0] = {
30 			.first = 0,
31 			.lower_first = 0,
32 			.count = 4294967295U,
33 		},
34 	},
35 	.gid_map = {
36 		.nr_extents = 1,
37 		.extent[0] = {
38 			.first = 0,
39 			.lower_first = 0,
40 			.count = 4294967295U,
41 		},
42 	},
43 	.projid_map = {
44 		.nr_extents = 1,
45 		.extent[0] = {
46 			.first = 0,
47 			.lower_first = 0,
48 			.count = 4294967295U,
49 		},
50 	},
51 	.count = ATOMIC_INIT(3),
52 	.owner = GLOBAL_ROOT_UID,
53 	.group = GLOBAL_ROOT_GID,
54 	.ns.inum = PROC_USER_INIT_INO,
55 #ifdef CONFIG_USER_NS
56 	.ns.ops = &userns_operations,
57 #endif
58 	.flags = USERNS_INIT_FLAGS,
59 #ifdef CONFIG_PERSISTENT_KEYRINGS
60 	.persistent_keyring_register_sem =
61 	__RWSEM_INITIALIZER(init_user_ns.persistent_keyring_register_sem),
62 #endif
63 };
64 EXPORT_SYMBOL_GPL(init_user_ns);
65 
66 /*
67  * UID task count cache, to get fast user lookup in "alloc_uid"
68  * when changing user ID's (ie setuid() and friends).
69  */
70 
71 #define UIDHASH_BITS	(CONFIG_BASE_SMALL ? 3 : 7)
72 #define UIDHASH_SZ	(1 << UIDHASH_BITS)
73 #define UIDHASH_MASK		(UIDHASH_SZ - 1)
74 #define __uidhashfn(uid)	(((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK)
75 #define uidhashentry(uid)	(uidhash_table + __uidhashfn((__kuid_val(uid))))
76 
77 static struct kmem_cache *uid_cachep;
78 struct hlist_head uidhash_table[UIDHASH_SZ];
79 
80 /*
81  * The uidhash_lock is mostly taken from process context, but it is
82  * occasionally also taken from softirq/tasklet context, when
83  * task-structs get RCU-freed. Hence all locking must be softirq-safe.
84  * But free_uid() is also called with local interrupts disabled, and running
85  * local_bh_enable() with local interrupts disabled is an error - we'll run
86  * softirq callbacks, and they can unconditionally enable interrupts, and
87  * the caller of free_uid() didn't expect that..
88  */
89 static DEFINE_SPINLOCK(uidhash_lock);
90 
91 /* root_user.__count is 1, for init task cred */
92 struct user_struct root_user = {
93 	.__count	= ATOMIC_INIT(1),
94 	.processes	= ATOMIC_INIT(1),
95 	.sigpending	= ATOMIC_INIT(0),
96 	.locked_shm     = 0,
97 	.uid		= GLOBAL_ROOT_UID,
98 };
99 
100 /*
101  * These routines must be called with the uidhash spinlock held!
102  */
uid_hash_insert(struct user_struct * up,struct hlist_head * hashent)103 static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent)
104 {
105 	hlist_add_head(&up->uidhash_node, hashent);
106 }
107 
uid_hash_remove(struct user_struct * up)108 static void uid_hash_remove(struct user_struct *up)
109 {
110 	hlist_del_init(&up->uidhash_node);
111 }
112 
uid_hash_find(kuid_t uid,struct hlist_head * hashent)113 static struct user_struct *uid_hash_find(kuid_t uid, struct hlist_head *hashent)
114 {
115 	struct user_struct *user;
116 
117 	hlist_for_each_entry(user, hashent, uidhash_node) {
118 		if (uid_eq(user->uid, uid)) {
119 			atomic_inc(&user->__count);
120 			return user;
121 		}
122 	}
123 
124 	return NULL;
125 }
126 
127 /* IRQs are disabled and uidhash_lock is held upon function entry.
128  * IRQ state (as stored in flags) is restored and uidhash_lock released
129  * upon function exit.
130  */
free_user(struct user_struct * up,unsigned long flags)131 static void free_user(struct user_struct *up, unsigned long flags)
132 	__releases(&uidhash_lock)
133 {
134 	uid_hash_remove(up);
135 	spin_unlock_irqrestore(&uidhash_lock, flags);
136 	key_put(up->uid_keyring);
137 	key_put(up->session_keyring);
138 	kmem_cache_free(uid_cachep, up);
139 }
140 
141 /*
142  * Locate the user_struct for the passed UID.  If found, take a ref on it.  The
143  * caller must undo that ref with free_uid().
144  *
145  * If the user_struct could not be found, return NULL.
146  */
find_user(kuid_t uid)147 struct user_struct *find_user(kuid_t uid)
148 {
149 	struct user_struct *ret;
150 	unsigned long flags;
151 
152 	spin_lock_irqsave(&uidhash_lock, flags);
153 	ret = uid_hash_find(uid, uidhashentry(uid));
154 	spin_unlock_irqrestore(&uidhash_lock, flags);
155 	return ret;
156 }
157 
free_uid(struct user_struct * up)158 void free_uid(struct user_struct *up)
159 {
160 	unsigned long flags;
161 
162 	if (!up)
163 		return;
164 
165 	local_irq_save(flags);
166 	if (atomic_dec_and_lock(&up->__count, &uidhash_lock))
167 		free_user(up, flags);
168 	else
169 		local_irq_restore(flags);
170 }
171 
alloc_uid(kuid_t uid)172 struct user_struct *alloc_uid(kuid_t uid)
173 {
174 	struct hlist_head *hashent = uidhashentry(uid);
175 	struct user_struct *up, *new;
176 
177 	spin_lock_irq(&uidhash_lock);
178 	up = uid_hash_find(uid, hashent);
179 	spin_unlock_irq(&uidhash_lock);
180 
181 	if (!up) {
182 		new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL);
183 		if (!new)
184 			goto out_unlock;
185 
186 		new->uid = uid;
187 		atomic_set(&new->__count, 1);
188 
189 		/*
190 		 * Before adding this, check whether we raced
191 		 * on adding the same user already..
192 		 */
193 		spin_lock_irq(&uidhash_lock);
194 		up = uid_hash_find(uid, hashent);
195 		if (up) {
196 			key_put(new->uid_keyring);
197 			key_put(new->session_keyring);
198 			kmem_cache_free(uid_cachep, new);
199 		} else {
200 			uid_hash_insert(new, hashent);
201 			up = new;
202 		}
203 		spin_unlock_irq(&uidhash_lock);
204 	}
205 	proc_register_uid(uid);
206 
207 	return up;
208 
209 out_unlock:
210 	return NULL;
211 }
212 
uid_cache_init(void)213 static int __init uid_cache_init(void)
214 {
215 	int n;
216 
217 	uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
218 			0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
219 
220 	for(n = 0; n < UIDHASH_SZ; ++n)
221 		INIT_HLIST_HEAD(uidhash_table + n);
222 
223 	/* Insert the root user immediately (init already runs as root) */
224 	spin_lock_irq(&uidhash_lock);
225 	uid_hash_insert(&root_user, uidhashentry(GLOBAL_ROOT_UID));
226 	spin_unlock_irq(&uidhash_lock);
227 	proc_register_uid(GLOBAL_ROOT_UID);
228 
229 	return 0;
230 }
231 subsys_initcall(uid_cache_init);
232