1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  * The "user cache".
4  *
5  * (C) Copyright 1991-2000 Linus Torvalds
6  *
7  * We have a per-user structure to keep track of how many
8  * processes, files etc the user has claimed, in order to be
9  * able to have per-user limits for system resources.
10  */
11 
12 #include <linux/init.h>
13 #include <linux/sched.h>
14 #include <linux/slab.h>
15 #include <linux/bitops.h>
16 #include <linux/key.h>
17 #include <linux/sched/user.h>
18 #include <linux/interrupt.h>
19 #include <linux/export.h>
20 #include <linux/user_namespace.h>
21 #include <linux/proc_ns.h>
22 
23 /*
24  * userns count is 1 for root user, 1 for init_uts_ns,
25  * and 1 for... ?
26  */
27 struct user_namespace init_user_ns = {
28 	.uid_map = {
29 		.nr_extents = 1,
30 		{
31 			.extent[0] = {
32 				.first = 0,
33 				.lower_first = 0,
34 				.count = 4294967295U,
35 			},
36 		},
37 	},
38 	.gid_map = {
39 		.nr_extents = 1,
40 		{
41 			.extent[0] = {
42 				.first = 0,
43 				.lower_first = 0,
44 				.count = 4294967295U,
45 			},
46 		},
47 	},
48 	.projid_map = {
49 		.nr_extents = 1,
50 		{
51 			.extent[0] = {
52 				.first = 0,
53 				.lower_first = 0,
54 				.count = 4294967295U,
55 			},
56 		},
57 	},
58 	.ns.count = REFCOUNT_INIT(3),
59 	.owner = GLOBAL_ROOT_UID,
60 	.group = GLOBAL_ROOT_GID,
61 	.ns.inum = PROC_USER_INIT_INO,
62 #ifdef CONFIG_USER_NS
63 	.ns.ops = &userns_operations,
64 #endif
65 	.flags = USERNS_INIT_FLAGS,
66 #ifdef CONFIG_KEYS
67 	.keyring_name_list = LIST_HEAD_INIT(init_user_ns.keyring_name_list),
68 	.keyring_sem = __RWSEM_INITIALIZER(init_user_ns.keyring_sem),
69 #endif
70 };
71 EXPORT_SYMBOL_GPL(init_user_ns);
72 
73 /*
74  * UID task count cache, to get fast user lookup in "alloc_uid"
75  * when changing user ID's (ie setuid() and friends).
76  */
77 
78 #define UIDHASH_BITS	(CONFIG_BASE_SMALL ? 3 : 7)
79 #define UIDHASH_SZ	(1 << UIDHASH_BITS)
80 #define UIDHASH_MASK		(UIDHASH_SZ - 1)
81 #define __uidhashfn(uid)	(((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK)
82 #define uidhashentry(uid)	(uidhash_table + __uidhashfn((__kuid_val(uid))))
83 
84 static struct kmem_cache *uid_cachep;
85 static struct hlist_head uidhash_table[UIDHASH_SZ];
86 
87 /*
88  * The uidhash_lock is mostly taken from process context, but it is
89  * occasionally also taken from softirq/tasklet context, when
90  * task-structs get RCU-freed. Hence all locking must be softirq-safe.
91  * But free_uid() is also called with local interrupts disabled, and running
92  * local_bh_enable() with local interrupts disabled is an error - we'll run
93  * softirq callbacks, and they can unconditionally enable interrupts, and
94  * the caller of free_uid() didn't expect that..
95  */
96 static DEFINE_SPINLOCK(uidhash_lock);
97 
98 /* root_user.__count is 1, for init task cred */
99 struct user_struct root_user = {
100 	.__count	= REFCOUNT_INIT(1),
101 	.uid		= GLOBAL_ROOT_UID,
102 	.ratelimit	= RATELIMIT_STATE_INIT(root_user.ratelimit, 0, 0),
103 };
104 
105 /*
106  * These routines must be called with the uidhash spinlock held!
107  */
uid_hash_insert(struct user_struct * up,struct hlist_head * hashent)108 static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent)
109 {
110 	hlist_add_head(&up->uidhash_node, hashent);
111 }
112 
uid_hash_remove(struct user_struct * up)113 static void uid_hash_remove(struct user_struct *up)
114 {
115 	hlist_del_init(&up->uidhash_node);
116 }
117 
uid_hash_find(kuid_t uid,struct hlist_head * hashent)118 static struct user_struct *uid_hash_find(kuid_t uid, struct hlist_head *hashent)
119 {
120 	struct user_struct *user;
121 
122 	hlist_for_each_entry(user, hashent, uidhash_node) {
123 		if (uid_eq(user->uid, uid)) {
124 			refcount_inc(&user->__count);
125 			return user;
126 		}
127 	}
128 
129 	return NULL;
130 }
131 
user_epoll_alloc(struct user_struct * up)132 static int user_epoll_alloc(struct user_struct *up)
133 {
134 #ifdef CONFIG_EPOLL
135 	return percpu_counter_init(&up->epoll_watches, 0, GFP_KERNEL);
136 #else
137 	return 0;
138 #endif
139 }
140 
user_epoll_free(struct user_struct * up)141 static void user_epoll_free(struct user_struct *up)
142 {
143 #ifdef CONFIG_EPOLL
144 	percpu_counter_destroy(&up->epoll_watches);
145 #endif
146 }
147 
148 /* IRQs are disabled and uidhash_lock is held upon function entry.
149  * IRQ state (as stored in flags) is restored and uidhash_lock released
150  * upon function exit.
151  */
free_user(struct user_struct * up,unsigned long flags)152 static void free_user(struct user_struct *up, unsigned long flags)
153 	__releases(&uidhash_lock)
154 {
155 	uid_hash_remove(up);
156 	spin_unlock_irqrestore(&uidhash_lock, flags);
157 	user_epoll_free(up);
158 	kmem_cache_free(uid_cachep, up);
159 }
160 
161 /*
162  * Locate the user_struct for the passed UID.  If found, take a ref on it.  The
163  * caller must undo that ref with free_uid().
164  *
165  * If the user_struct could not be found, return NULL.
166  */
find_user(kuid_t uid)167 struct user_struct *find_user(kuid_t uid)
168 {
169 	struct user_struct *ret;
170 	unsigned long flags;
171 
172 	spin_lock_irqsave(&uidhash_lock, flags);
173 	ret = uid_hash_find(uid, uidhashentry(uid));
174 	spin_unlock_irqrestore(&uidhash_lock, flags);
175 	return ret;
176 }
177 
free_uid(struct user_struct * up)178 void free_uid(struct user_struct *up)
179 {
180 	unsigned long flags;
181 
182 	if (!up)
183 		return;
184 
185 	if (refcount_dec_and_lock_irqsave(&up->__count, &uidhash_lock, &flags))
186 		free_user(up, flags);
187 }
188 EXPORT_SYMBOL_GPL(free_uid);
189 
alloc_uid(kuid_t uid)190 struct user_struct *alloc_uid(kuid_t uid)
191 {
192 	struct hlist_head *hashent = uidhashentry(uid);
193 	struct user_struct *up, *new;
194 
195 	spin_lock_irq(&uidhash_lock);
196 	up = uid_hash_find(uid, hashent);
197 	spin_unlock_irq(&uidhash_lock);
198 
199 	if (!up) {
200 		new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL);
201 		if (!new)
202 			return NULL;
203 
204 		new->uid = uid;
205 		refcount_set(&new->__count, 1);
206 		if (user_epoll_alloc(new)) {
207 			kmem_cache_free(uid_cachep, new);
208 			return NULL;
209 		}
210 		ratelimit_state_init(&new->ratelimit, HZ, 100);
211 		ratelimit_set_flags(&new->ratelimit, RATELIMIT_MSG_ON_RELEASE);
212 
213 		/*
214 		 * Before adding this, check whether we raced
215 		 * on adding the same user already..
216 		 */
217 		spin_lock_irq(&uidhash_lock);
218 		up = uid_hash_find(uid, hashent);
219 		if (up) {
220 			user_epoll_free(new);
221 			kmem_cache_free(uid_cachep, new);
222 		} else {
223 			uid_hash_insert(new, hashent);
224 			up = new;
225 		}
226 		spin_unlock_irq(&uidhash_lock);
227 	}
228 
229 	return up;
230 }
231 
uid_cache_init(void)232 static int __init uid_cache_init(void)
233 {
234 	int n;
235 
236 	uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
237 			0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
238 
239 	for(n = 0; n < UIDHASH_SZ; ++n)
240 		INIT_HLIST_HEAD(uidhash_table + n);
241 
242 	if (user_epoll_alloc(&root_user))
243 		panic("root_user epoll percpu counter alloc failed");
244 
245 	/* Insert the root user immediately (init already runs as root) */
246 	spin_lock_irq(&uidhash_lock);
247 	uid_hash_insert(&root_user, uidhashentry(GLOBAL_ROOT_UID));
248 	spin_unlock_irq(&uidhash_lock);
249 
250 	return 0;
251 }
252 subsys_initcall(uid_cache_init);
253