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 (IS_ENABLED(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(&up->uidhash_node, hashent); 124 } 125 126 static void uid_hash_remove(struct user_struct *up) 127 { 128 hlist_del_init(&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(user->uid, uid)) { 137 refcount_inc(&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(&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(&uidhash_lock, flags); 170 user_epoll_free(up); 171 kmem_cache_free(uid_cachep, 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(&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(&up->__count, &uidhash_lock, &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(&uidhash_lock); 209 up = uid_hash_find(uid, hashent); 210 spin_unlock_irq(&uidhash_lock); 211 212 if (!up) { 213 new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL); 214 if (!new) 215 return NULL; 216 217 new->uid = uid; 218 refcount_set(&new->__count, 1); 219 if (user_epoll_alloc(new)) { 220 kmem_cache_free(uid_cachep, new); 221 return NULL; 222 } 223 ratelimit_state_init(&new->ratelimit, HZ, 100); 224 ratelimit_set_flags(&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(&uidhash_lock); 231 up = uid_hash_find(uid, hashent); 232 if (up) { 233 user_epoll_free(new); 234 kmem_cache_free(uid_cachep, new); 235 } else { 236 uid_hash_insert(new, hashent); 237 up = new; 238 } 239 spin_unlock_irq(&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("uid_cache", sizeof(struct user_struct), 250 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(&root_user)) 256 panic("root_user epoll percpu counter alloc failed"); 257 258 /* Insert the root user immediately (init already runs as root) */ 259 spin_lock_irq(&uidhash_lock); 260 uid_hash_insert(&root_user, uidhashentry(GLOBAL_ROOT_UID)); 261 spin_unlock_irq(&uidhash_lock); 262 263 return 0; 264 } 265 subsys_initcall(uid_cache_init); 266