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