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/binfmts.h> |
22 | #include <linux/proc_ns.h> |
23 | |
24 | #if IS_ENABLED(CONFIG_BINFMT_MISC) |
25 | struct binfmt_misc init_binfmt_misc = { |
26 | .entries = LIST_HEAD_INIT(init_binfmt_misc.entries), |
27 | .enabled = true, |
28 | .entries_lock = __RW_LOCK_UNLOCKED(init_binfmt_misc.entries_lock), |
29 | }; |
30 | EXPORT_SYMBOL_GPL(init_binfmt_misc); |
31 | #endif |
32 | |
33 | /* |
34 | * userns count is 1 for root user, 1 for init_uts_ns, |
35 | * and 1 for... ? |
36 | */ |
37 | struct user_namespace init_user_ns = { |
38 | .uid_map = { |
39 | .nr_extents = 1, |
40 | { |
41 | .extent[0] = { |
42 | .first = 0, |
43 | .lower_first = 0, |
44 | .count = 4294967295U, |
45 | }, |
46 | }, |
47 | }, |
48 | .gid_map = { |
49 | .nr_extents = 1, |
50 | { |
51 | .extent[0] = { |
52 | .first = 0, |
53 | .lower_first = 0, |
54 | .count = 4294967295U, |
55 | }, |
56 | }, |
57 | }, |
58 | .projid_map = { |
59 | .nr_extents = 1, |
60 | { |
61 | .extent[0] = { |
62 | .first = 0, |
63 | .lower_first = 0, |
64 | .count = 4294967295U, |
65 | }, |
66 | }, |
67 | }, |
68 | .ns.count = REFCOUNT_INIT(3), |
69 | .owner = GLOBAL_ROOT_UID, |
70 | .group = GLOBAL_ROOT_GID, |
71 | .ns.inum = PROC_USER_INIT_INO, |
72 | #ifdef CONFIG_USER_NS |
73 | .ns.ops = &userns_operations, |
74 | #endif |
75 | .flags = USERNS_INIT_FLAGS, |
76 | #ifdef CONFIG_KEYS |
77 | .keyring_name_list = LIST_HEAD_INIT(init_user_ns.keyring_name_list), |
78 | .keyring_sem = __RWSEM_INITIALIZER(init_user_ns.keyring_sem), |
79 | #endif |
80 | #if IS_ENABLED(CONFIG_BINFMT_MISC) |
81 | .binfmt_misc = &init_binfmt_misc, |
82 | #endif |
83 | }; |
84 | EXPORT_SYMBOL_GPL(init_user_ns); |
85 | |
86 | /* |
87 | * UID task count cache, to get fast user lookup in "alloc_uid" |
88 | * when changing user ID's (ie setuid() and friends). |
89 | */ |
90 | |
91 | #define UIDHASH_BITS (CONFIG_BASE_SMALL ? 3 : 7) |
92 | #define UIDHASH_SZ (1 << UIDHASH_BITS) |
93 | #define UIDHASH_MASK (UIDHASH_SZ - 1) |
94 | #define __uidhashfn(uid) (((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK) |
95 | #define uidhashentry(uid) (uidhash_table + __uidhashfn((__kuid_val(uid)))) |
96 | |
97 | static struct kmem_cache *uid_cachep; |
98 | static struct hlist_head uidhash_table[UIDHASH_SZ]; |
99 | |
100 | /* |
101 | * The uidhash_lock is mostly taken from process context, but it is |
102 | * occasionally also taken from softirq/tasklet context, when |
103 | * task-structs get RCU-freed. Hence all locking must be softirq-safe. |
104 | * But free_uid() is also called with local interrupts disabled, and running |
105 | * local_bh_enable() with local interrupts disabled is an error - we'll run |
106 | * softirq callbacks, and they can unconditionally enable interrupts, and |
107 | * the caller of free_uid() didn't expect that.. |
108 | */ |
109 | static DEFINE_SPINLOCK(uidhash_lock); |
110 | |
111 | /* root_user.__count is 1, for init task cred */ |
112 | struct user_struct root_user = { |
113 | .__count = REFCOUNT_INIT(1), |
114 | .uid = GLOBAL_ROOT_UID, |
115 | .ratelimit = RATELIMIT_STATE_INIT(root_user.ratelimit, 0, 0), |
116 | }; |
117 | |
118 | /* |
119 | * These routines must be called with the uidhash spinlock held! |
120 | */ |
121 | static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent) |
122 | { |
123 | hlist_add_head(n: &up->uidhash_node, h: hashent); |
124 | } |
125 | |
126 | static void uid_hash_remove(struct user_struct *up) |
127 | { |
128 | hlist_del_init(n: &up->uidhash_node); |
129 | } |
130 | |
131 | static struct user_struct *uid_hash_find(kuid_t uid, struct hlist_head *hashent) |
132 | { |
133 | struct user_struct *user; |
134 | |
135 | hlist_for_each_entry(user, hashent, uidhash_node) { |
136 | if (uid_eq(left: user->uid, right: uid)) { |
137 | refcount_inc(r: &user->__count); |
138 | return user; |
139 | } |
140 | } |
141 | |
142 | return NULL; |
143 | } |
144 | |
145 | static int user_epoll_alloc(struct user_struct *up) |
146 | { |
147 | #ifdef CONFIG_EPOLL |
148 | return percpu_counter_init(&up->epoll_watches, 0, GFP_KERNEL); |
149 | #else |
150 | return 0; |
151 | #endif |
152 | } |
153 | |
154 | static void user_epoll_free(struct user_struct *up) |
155 | { |
156 | #ifdef CONFIG_EPOLL |
157 | percpu_counter_destroy(fbc: &up->epoll_watches); |
158 | #endif |
159 | } |
160 | |
161 | /* IRQs are disabled and uidhash_lock is held upon function entry. |
162 | * IRQ state (as stored in flags) is restored and uidhash_lock released |
163 | * upon function exit. |
164 | */ |
165 | static void free_user(struct user_struct *up, unsigned long flags) |
166 | __releases(&uidhash_lock) |
167 | { |
168 | uid_hash_remove(up); |
169 | spin_unlock_irqrestore(lock: &uidhash_lock, flags); |
170 | user_epoll_free(up); |
171 | kmem_cache_free(s: uid_cachep, objp: up); |
172 | } |
173 | |
174 | /* |
175 | * Locate the user_struct for the passed UID. If found, take a ref on it. The |
176 | * caller must undo that ref with free_uid(). |
177 | * |
178 | * If the user_struct could not be found, return NULL. |
179 | */ |
180 | struct user_struct *find_user(kuid_t uid) |
181 | { |
182 | struct user_struct *ret; |
183 | unsigned long flags; |
184 | |
185 | spin_lock_irqsave(&uidhash_lock, flags); |
186 | ret = uid_hash_find(uid, uidhashentry(uid)); |
187 | spin_unlock_irqrestore(lock: &uidhash_lock, flags); |
188 | return ret; |
189 | } |
190 | |
191 | void free_uid(struct user_struct *up) |
192 | { |
193 | unsigned long flags; |
194 | |
195 | if (!up) |
196 | return; |
197 | |
198 | if (refcount_dec_and_lock_irqsave(r: &up->__count, lock: &uidhash_lock, flags: &flags)) |
199 | free_user(up, flags); |
200 | } |
201 | EXPORT_SYMBOL_GPL(free_uid); |
202 | |
203 | struct user_struct *alloc_uid(kuid_t uid) |
204 | { |
205 | struct hlist_head *hashent = uidhashentry(uid); |
206 | struct user_struct *up, *new; |
207 | |
208 | spin_lock_irq(lock: &uidhash_lock); |
209 | up = uid_hash_find(uid, hashent); |
210 | spin_unlock_irq(lock: &uidhash_lock); |
211 | |
212 | if (!up) { |
213 | new = kmem_cache_zalloc(k: uid_cachep, GFP_KERNEL); |
214 | if (!new) |
215 | return NULL; |
216 | |
217 | new->uid = uid; |
218 | refcount_set(r: &new->__count, n: 1); |
219 | if (user_epoll_alloc(up: new)) { |
220 | kmem_cache_free(s: uid_cachep, objp: new); |
221 | return NULL; |
222 | } |
223 | ratelimit_state_init(rs: &new->ratelimit, HZ, burst: 100); |
224 | ratelimit_set_flags(rs: &new->ratelimit, RATELIMIT_MSG_ON_RELEASE); |
225 | |
226 | /* |
227 | * Before adding this, check whether we raced |
228 | * on adding the same user already.. |
229 | */ |
230 | spin_lock_irq(lock: &uidhash_lock); |
231 | up = uid_hash_find(uid, hashent); |
232 | if (up) { |
233 | user_epoll_free(up: new); |
234 | kmem_cache_free(s: uid_cachep, objp: new); |
235 | } else { |
236 | uid_hash_insert(up: new, hashent); |
237 | up = new; |
238 | } |
239 | spin_unlock_irq(lock: &uidhash_lock); |
240 | } |
241 | |
242 | return up; |
243 | } |
244 | |
245 | static int __init uid_cache_init(void) |
246 | { |
247 | int n; |
248 | |
249 | uid_cachep = kmem_cache_create(name: "uid_cache" , size: sizeof(struct user_struct), |
250 | align: 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL); |
251 | |
252 | for(n = 0; n < UIDHASH_SZ; ++n) |
253 | INIT_HLIST_HEAD(uidhash_table + n); |
254 | |
255 | if (user_epoll_alloc(up: &root_user)) |
256 | panic(fmt: "root_user epoll percpu counter alloc failed" ); |
257 | |
258 | /* Insert the root user immediately (init already runs as root) */ |
259 | spin_lock_irq(lock: &uidhash_lock); |
260 | uid_hash_insert(up: &root_user, uidhashentry(GLOBAL_ROOT_UID)); |
261 | spin_unlock_irq(&uidhash_lock); |
262 | |
263 | return 0; |
264 | } |
265 | subsys_initcall(uid_cache_init); |
266 | |