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 { 40 .extent[0] = { 41 .first = 0, 42 .lower_first = 0, 43 .count = 4294967295U, 44 }, 45 .nr_extents = 1, 46 }, 47 }, 48 .gid_map = { 49 { 50 .extent[0] = { 51 .first = 0, 52 .lower_first = 0, 53 .count = 4294967295U, 54 }, 55 .nr_extents = 1, 56 }, 57 }, 58 .projid_map = { 59 { 60 .extent[0] = { 61 .first = 0, 62 .lower_first = 0, 63 .count = 4294967295U, 64 }, 65 .nr_extents = 1, 66 }, 67 }, 68 .ns.ns_type = ns_common_type(&init_user_ns), 69 .ns.__ns_ref = REFCOUNT_INIT(3), 70 .owner = GLOBAL_ROOT_UID, 71 .group = GLOBAL_ROOT_GID, 72 .ns.inum = ns_init_inum(&init_user_ns), 73 #ifdef CONFIG_USER_NS 74 .ns.ops = &userns_operations, 75 #endif 76 .flags = USERNS_INIT_FLAGS, 77 #ifdef CONFIG_KEYS 78 .keyring_name_list = LIST_HEAD_INIT(init_user_ns.keyring_name_list), 79 .keyring_sem = __RWSEM_INITIALIZER(init_user_ns.keyring_sem), 80 #endif 81 #if IS_ENABLED(CONFIG_BINFMT_MISC) 82 .binfmt_misc = &init_binfmt_misc, 83 #endif 84 }; 85 EXPORT_SYMBOL_GPL(init_user_ns); 86 87 /* 88 * UID task count cache, to get fast user lookup in "alloc_uid" 89 * when changing user ID's (ie setuid() and friends). 90 */ 91 92 #define UIDHASH_BITS (IS_ENABLED(CONFIG_BASE_SMALL) ? 3 : 7) 93 #define UIDHASH_SZ (1 << UIDHASH_BITS) 94 #define UIDHASH_MASK (UIDHASH_SZ - 1) 95 #define __uidhashfn(uid) (((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK) 96 #define uidhashentry(uid) (uidhash_table + __uidhashfn((__kuid_val(uid)))) 97 98 static struct kmem_cache *uid_cachep; 99 static struct hlist_head uidhash_table[UIDHASH_SZ]; 100 101 /* 102 * The uidhash_lock is mostly taken from process context, but it is 103 * occasionally also taken from softirq/tasklet context, when 104 * task-structs get RCU-freed. Hence all locking must be softirq-safe. 105 * But free_uid() is also called with local interrupts disabled, and running 106 * local_bh_enable() with local interrupts disabled is an error - we'll run 107 * softirq callbacks, and they can unconditionally enable interrupts, and 108 * the caller of free_uid() didn't expect that.. 109 */ 110 static DEFINE_SPINLOCK(uidhash_lock); 111 112 /* root_user.__count is 1, for init task cred */ 113 struct user_struct root_user = { 114 .__count = REFCOUNT_INIT(1), 115 .uid = GLOBAL_ROOT_UID, 116 .ratelimit = RATELIMIT_STATE_INIT(root_user.ratelimit, 0, 0), 117 }; 118 119 /* 120 * These routines must be called with the uidhash spinlock held! 121 */ 122 static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent) 123 { 124 hlist_add_head(&up->uidhash_node, hashent); 125 } 126 127 static void uid_hash_remove(struct user_struct *up) 128 { 129 hlist_del_init(&up->uidhash_node); 130 } 131 132 static struct user_struct *uid_hash_find(kuid_t uid, struct hlist_head *hashent) 133 { 134 struct user_struct *user; 135 136 hlist_for_each_entry(user, hashent, uidhash_node) { 137 if (uid_eq(user->uid, uid)) { 138 refcount_inc(&user->__count); 139 return user; 140 } 141 } 142 143 return NULL; 144 } 145 146 static int user_epoll_alloc(struct user_struct *up) 147 { 148 #ifdef CONFIG_EPOLL 149 return percpu_counter_init(&up->epoll_watches, 0, GFP_KERNEL); 150 #else 151 return 0; 152 #endif 153 } 154 155 static void user_epoll_free(struct user_struct *up) 156 { 157 #ifdef CONFIG_EPOLL 158 percpu_counter_destroy(&up->epoll_watches); 159 #endif 160 } 161 162 /* IRQs are disabled and uidhash_lock is held upon function entry. 163 * IRQ state (as stored in flags) is restored and uidhash_lock released 164 * upon function exit. 165 */ 166 static void free_user(struct user_struct *up, unsigned long flags) 167 __releases(&uidhash_lock) 168 { 169 uid_hash_remove(up); 170 spin_unlock_irqrestore(&uidhash_lock, flags); 171 user_epoll_free(up); 172 kmem_cache_free(uid_cachep, up); 173 } 174 175 /* 176 * Locate the user_struct for the passed UID. If found, take a ref on it. The 177 * caller must undo that ref with free_uid(). 178 * 179 * If the user_struct could not be found, return NULL. 180 */ 181 struct user_struct *find_user(kuid_t uid) 182 { 183 struct user_struct *ret; 184 unsigned long flags; 185 186 spin_lock_irqsave(&uidhash_lock, flags); 187 ret = uid_hash_find(uid, uidhashentry(uid)); 188 spin_unlock_irqrestore(&uidhash_lock, flags); 189 return ret; 190 } 191 192 void free_uid(struct user_struct *up) 193 { 194 unsigned long flags; 195 196 if (!up) 197 return; 198 199 if (refcount_dec_and_lock_irqsave(&up->__count, &uidhash_lock, &flags)) 200 free_user(up, flags); 201 } 202 EXPORT_SYMBOL_GPL(free_uid); 203 204 struct user_struct *alloc_uid(kuid_t uid) 205 { 206 struct hlist_head *hashent = uidhashentry(uid); 207 struct user_struct *up, *new; 208 209 spin_lock_irq(&uidhash_lock); 210 up = uid_hash_find(uid, hashent); 211 spin_unlock_irq(&uidhash_lock); 212 213 if (!up) { 214 new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL); 215 if (!new) 216 return NULL; 217 218 new->uid = uid; 219 refcount_set(&new->__count, 1); 220 if (user_epoll_alloc(new)) { 221 kmem_cache_free(uid_cachep, new); 222 return NULL; 223 } 224 ratelimit_state_init(&new->ratelimit, HZ, 100); 225 ratelimit_set_flags(&new->ratelimit, RATELIMIT_MSG_ON_RELEASE); 226 227 /* 228 * Before adding this, check whether we raced 229 * on adding the same user already.. 230 */ 231 spin_lock_irq(&uidhash_lock); 232 up = uid_hash_find(uid, hashent); 233 if (up) { 234 user_epoll_free(new); 235 kmem_cache_free(uid_cachep, new); 236 } else { 237 uid_hash_insert(new, hashent); 238 up = new; 239 } 240 spin_unlock_irq(&uidhash_lock); 241 } 242 243 return up; 244 } 245 246 static int __init uid_cache_init(void) 247 { 248 int n; 249 250 uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct), 251 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL); 252 253 for(n = 0; n < UIDHASH_SZ; ++n) 254 INIT_HLIST_HEAD(uidhash_table + n); 255 256 if (user_epoll_alloc(&root_user)) 257 panic("root_user epoll percpu counter alloc failed"); 258 259 /* Insert the root user immediately (init already runs as root) */ 260 spin_lock_irq(&uidhash_lock); 261 uid_hash_insert(&root_user, uidhashentry(GLOBAL_ROOT_UID)); 262 spin_unlock_irq(&uidhash_lock); 263 264 return 0; 265 } 266 subsys_initcall(uid_cache_init); 267