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 .locked_shm = 0, 102 .uid = GLOBAL_ROOT_UID, 103 .ratelimit = RATELIMIT_STATE_INIT(root_user.ratelimit, 0, 0), 104 }; 105 106 /* 107 * These routines must be called with the uidhash spinlock held! 108 */ 109 static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent) 110 { 111 hlist_add_head(&up->uidhash_node, hashent); 112 } 113 114 static void uid_hash_remove(struct user_struct *up) 115 { 116 hlist_del_init(&up->uidhash_node); 117 } 118 119 static struct user_struct *uid_hash_find(kuid_t uid, struct hlist_head *hashent) 120 { 121 struct user_struct *user; 122 123 hlist_for_each_entry(user, hashent, uidhash_node) { 124 if (uid_eq(user->uid, uid)) { 125 refcount_inc(&user->__count); 126 return user; 127 } 128 } 129 130 return NULL; 131 } 132 133 /* IRQs are disabled and uidhash_lock is held upon function entry. 134 * IRQ state (as stored in flags) is restored and uidhash_lock released 135 * upon function exit. 136 */ 137 static void free_user(struct user_struct *up, unsigned long flags) 138 __releases(&uidhash_lock) 139 { 140 uid_hash_remove(up); 141 spin_unlock_irqrestore(&uidhash_lock, flags); 142 kmem_cache_free(uid_cachep, up); 143 } 144 145 /* 146 * Locate the user_struct for the passed UID. If found, take a ref on it. The 147 * caller must undo that ref with free_uid(). 148 * 149 * If the user_struct could not be found, return NULL. 150 */ 151 struct user_struct *find_user(kuid_t uid) 152 { 153 struct user_struct *ret; 154 unsigned long flags; 155 156 spin_lock_irqsave(&uidhash_lock, flags); 157 ret = uid_hash_find(uid, uidhashentry(uid)); 158 spin_unlock_irqrestore(&uidhash_lock, flags); 159 return ret; 160 } 161 162 void free_uid(struct user_struct *up) 163 { 164 unsigned long flags; 165 166 if (!up) 167 return; 168 169 if (refcount_dec_and_lock_irqsave(&up->__count, &uidhash_lock, &flags)) 170 free_user(up, flags); 171 } 172 173 struct user_struct *alloc_uid(kuid_t uid) 174 { 175 struct hlist_head *hashent = uidhashentry(uid); 176 struct user_struct *up, *new; 177 178 spin_lock_irq(&uidhash_lock); 179 up = uid_hash_find(uid, hashent); 180 spin_unlock_irq(&uidhash_lock); 181 182 if (!up) { 183 new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL); 184 if (!new) 185 return NULL; 186 187 new->uid = uid; 188 refcount_set(&new->__count, 1); 189 ratelimit_state_init(&new->ratelimit, HZ, 100); 190 ratelimit_set_flags(&new->ratelimit, RATELIMIT_MSG_ON_RELEASE); 191 192 /* 193 * Before adding this, check whether we raced 194 * on adding the same user already.. 195 */ 196 spin_lock_irq(&uidhash_lock); 197 up = uid_hash_find(uid, hashent); 198 if (up) { 199 kmem_cache_free(uid_cachep, new); 200 } else { 201 uid_hash_insert(new, hashent); 202 up = new; 203 } 204 spin_unlock_irq(&uidhash_lock); 205 } 206 207 return up; 208 } 209 210 static int __init uid_cache_init(void) 211 { 212 int n; 213 214 uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct), 215 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL); 216 217 for(n = 0; n < UIDHASH_SZ; ++n) 218 INIT_HLIST_HEAD(uidhash_table + n); 219 220 /* Insert the root user immediately (init already runs as root) */ 221 spin_lock_irq(&uidhash_lock); 222 uid_hash_insert(&root_user, uidhashentry(GLOBAL_ROOT_UID)); 223 spin_unlock_irq(&uidhash_lock); 224 225 return 0; 226 } 227 subsys_initcall(uid_cache_init); 228