1 // SPDX-License-Identifier: GPL-2.0-only
5 * (C) Copyright 1991-2000 Linus Torvalds
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.
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>
24 * userns count is 1 for root user, 1 for init_uts_ns,
27 struct user_namespace init_user_ns = {
58 .ns.count = REFCOUNT_INIT(3),
59 .owner = GLOBAL_ROOT_UID,
60 .group = GLOBAL_ROOT_GID,
61 .ns.inum = PROC_USER_INIT_INO,
63 .ns.ops = &userns_operations,
65 .flags = USERNS_INIT_FLAGS,
67 .keyring_name_list = LIST_HEAD_INIT(init_user_ns.keyring_name_list),
68 .keyring_sem = __RWSEM_INITIALIZER(init_user_ns.keyring_sem),
71 EXPORT_SYMBOL_GPL(init_user_ns);
74 * UID task count cache, to get fast user lookup in "alloc_uid"
75 * when changing user ID's (ie setuid() and friends).
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))))
84 static struct kmem_cache *uid_cachep;
85 static struct hlist_head uidhash_table[UIDHASH_SZ];
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..
96 static DEFINE_SPINLOCK(uidhash_lock);
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),
106 * These routines must be called with the uidhash spinlock held!
108 static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent)
110 hlist_add_head(&up->uidhash_node, hashent);
113 static void uid_hash_remove(struct user_struct *up)
115 hlist_del_init(&up->uidhash_node);
118 static struct user_struct *uid_hash_find(kuid_t uid, struct hlist_head *hashent)
120 struct user_struct *user;
122 hlist_for_each_entry(user, hashent, uidhash_node) {
123 if (uid_eq(user->uid, uid)) {
124 refcount_inc(&user->__count);
132 static int user_epoll_alloc(struct user_struct *up)
135 return percpu_counter_init(&up->epoll_watches, 0, GFP_KERNEL);
141 static void user_epoll_free(struct user_struct *up)
144 percpu_counter_destroy(&up->epoll_watches);
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.
152 static void free_user(struct user_struct *up, unsigned long flags)
153 __releases(&uidhash_lock)
156 spin_unlock_irqrestore(&uidhash_lock, flags);
158 kmem_cache_free(uid_cachep, up);
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().
165 * If the user_struct could not be found, return NULL.
167 struct user_struct *find_user(kuid_t uid)
169 struct user_struct *ret;
172 spin_lock_irqsave(&uidhash_lock, flags);
173 ret = uid_hash_find(uid, uidhashentry(uid));
174 spin_unlock_irqrestore(&uidhash_lock, flags);
178 void free_uid(struct user_struct *up)
185 if (refcount_dec_and_lock_irqsave(&up->__count, &uidhash_lock, &flags))
186 free_user(up, flags);
189 struct user_struct *alloc_uid(kuid_t uid)
191 struct hlist_head *hashent = uidhashentry(uid);
192 struct user_struct *up, *new;
194 spin_lock_irq(&uidhash_lock);
195 up = uid_hash_find(uid, hashent);
196 spin_unlock_irq(&uidhash_lock);
199 new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL);
204 refcount_set(&new->__count, 1);
205 if (user_epoll_alloc(new)) {
206 kmem_cache_free(uid_cachep, new);
209 ratelimit_state_init(&new->ratelimit, HZ, 100);
210 ratelimit_set_flags(&new->ratelimit, RATELIMIT_MSG_ON_RELEASE);
213 * Before adding this, check whether we raced
214 * on adding the same user already..
216 spin_lock_irq(&uidhash_lock);
217 up = uid_hash_find(uid, hashent);
219 user_epoll_free(new);
220 kmem_cache_free(uid_cachep, new);
222 uid_hash_insert(new, hashent);
225 spin_unlock_irq(&uidhash_lock);
231 static int __init uid_cache_init(void)
235 uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
236 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
238 for(n = 0; n < UIDHASH_SZ; ++n)
239 INIT_HLIST_HEAD(uidhash_table + n);
241 if (user_epoll_alloc(&root_user))
242 panic("root_user epoll percpu counter alloc failed");
244 /* Insert the root user immediately (init already runs as root) */
245 spin_lock_irq(&uidhash_lock);
246 uid_hash_insert(&root_user, uidhashentry(GLOBAL_ROOT_UID));
247 spin_unlock_irq(&uidhash_lock);
251 subsys_initcall(uid_cache_init);