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 */ 108 static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent) 109 { 110 hlist_add_head(&up->uidhash_node, hashent); 111 } 112 113 static void uid_hash_remove(struct user_struct *up) 114 { 115 hlist_del_init(&up->uidhash_node); 116 } 117 118 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 } 131 132 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 } 140 141 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 */ 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 */ 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 } 177 178 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); 189 190 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 } 231 232 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