1 /* 2 * The "user cache". 3 * 4 * (C) Copyright 1991-2000 Linus Torvalds 5 * 6 * We have a per-user structure to keep track of how many 7 * processes, files etc the user has claimed, in order to be 8 * able to have per-user limits for system resources. 9 */ 10 11 #include <linux/init.h> 12 #include <linux/sched.h> 13 #include <linux/slab.h> 14 #include <linux/bitops.h> 15 #include <linux/key.h> 16 #include <linux/sched/user.h> 17 #include <linux/interrupt.h> 18 #include <linux/export.h> 19 #include <linux/user_namespace.h> 20 #include <linux/proc_ns.h> 21 22 /* 23 * userns count is 1 for root user, 1 for init_uts_ns, 24 * and 1 for... ? 25 */ 26 struct user_namespace init_user_ns = { 27 .uid_map = { 28 .nr_extents = 1, 29 { 30 .extent[0] = { 31 .first = 0, 32 .lower_first = 0, 33 .count = 4294967295U, 34 }, 35 }, 36 }, 37 .gid_map = { 38 .nr_extents = 1, 39 { 40 .extent[0] = { 41 .first = 0, 42 .lower_first = 0, 43 .count = 4294967295U, 44 }, 45 }, 46 }, 47 .projid_map = { 48 .nr_extents = 1, 49 { 50 .extent[0] = { 51 .first = 0, 52 .lower_first = 0, 53 .count = 4294967295U, 54 }, 55 }, 56 }, 57 .count = ATOMIC_INIT(3), 58 .owner = GLOBAL_ROOT_UID, 59 .group = GLOBAL_ROOT_GID, 60 .ns.inum = PROC_USER_INIT_INO, 61 #ifdef CONFIG_USER_NS 62 .ns.ops = &userns_operations, 63 #endif 64 .flags = USERNS_INIT_FLAGS, 65 #ifdef CONFIG_PERSISTENT_KEYRINGS 66 .persistent_keyring_register_sem = 67 __RWSEM_INITIALIZER(init_user_ns.persistent_keyring_register_sem), 68 #endif 69 }; 70 EXPORT_SYMBOL_GPL(init_user_ns); 71 72 /* 73 * UID task count cache, to get fast user lookup in "alloc_uid" 74 * when changing user ID's (ie setuid() and friends). 75 */ 76 77 #define UIDHASH_BITS (CONFIG_BASE_SMALL ? 3 : 7) 78 #define UIDHASH_SZ (1 << UIDHASH_BITS) 79 #define UIDHASH_MASK (UIDHASH_SZ - 1) 80 #define __uidhashfn(uid) (((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK) 81 #define uidhashentry(uid) (uidhash_table + __uidhashfn((__kuid_val(uid)))) 82 83 static struct kmem_cache *uid_cachep; 84 struct hlist_head uidhash_table[UIDHASH_SZ]; 85 86 /* 87 * The uidhash_lock is mostly taken from process context, but it is 88 * occasionally also taken from softirq/tasklet context, when 89 * task-structs get RCU-freed. Hence all locking must be softirq-safe. 90 * But free_uid() is also called with local interrupts disabled, and running 91 * local_bh_enable() with local interrupts disabled is an error - we'll run 92 * softirq callbacks, and they can unconditionally enable interrupts, and 93 * the caller of free_uid() didn't expect that.. 94 */ 95 static DEFINE_SPINLOCK(uidhash_lock); 96 97 /* root_user.__count is 1, for init task cred */ 98 struct user_struct root_user = { 99 .__count = ATOMIC_INIT(1), 100 .processes = ATOMIC_INIT(1), 101 .sigpending = ATOMIC_INIT(0), 102 .locked_shm = 0, 103 .uid = GLOBAL_ROOT_UID, 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 atomic_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 key_put(up->uid_keyring); 143 key_put(up->session_keyring); 144 kmem_cache_free(uid_cachep, up); 145 } 146 147 /* 148 * Locate the user_struct for the passed UID. If found, take a ref on it. The 149 * caller must undo that ref with free_uid(). 150 * 151 * If the user_struct could not be found, return NULL. 152 */ 153 struct user_struct *find_user(kuid_t uid) 154 { 155 struct user_struct *ret; 156 unsigned long flags; 157 158 spin_lock_irqsave(&uidhash_lock, flags); 159 ret = uid_hash_find(uid, uidhashentry(uid)); 160 spin_unlock_irqrestore(&uidhash_lock, flags); 161 return ret; 162 } 163 164 void free_uid(struct user_struct *up) 165 { 166 unsigned long flags; 167 168 if (!up) 169 return; 170 171 local_irq_save(flags); 172 if (atomic_dec_and_lock(&up->__count, &uidhash_lock)) 173 free_user(up, flags); 174 else 175 local_irq_restore(flags); 176 } 177 178 struct user_struct *alloc_uid(kuid_t uid) 179 { 180 struct hlist_head *hashent = uidhashentry(uid); 181 struct user_struct *up, *new; 182 183 spin_lock_irq(&uidhash_lock); 184 up = uid_hash_find(uid, hashent); 185 spin_unlock_irq(&uidhash_lock); 186 187 if (!up) { 188 new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL); 189 if (!new) 190 goto out_unlock; 191 192 new->uid = uid; 193 atomic_set(&new->__count, 1); 194 195 /* 196 * Before adding this, check whether we raced 197 * on adding the same user already.. 198 */ 199 spin_lock_irq(&uidhash_lock); 200 up = uid_hash_find(uid, hashent); 201 if (up) { 202 key_put(new->uid_keyring); 203 key_put(new->session_keyring); 204 kmem_cache_free(uid_cachep, new); 205 } else { 206 uid_hash_insert(new, hashent); 207 up = new; 208 } 209 spin_unlock_irq(&uidhash_lock); 210 } 211 212 return up; 213 214 out_unlock: 215 return NULL; 216 } 217 218 static int __init uid_cache_init(void) 219 { 220 int n; 221 222 uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct), 223 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL); 224 225 for(n = 0; n < UIDHASH_SZ; ++n) 226 INIT_HLIST_HEAD(uidhash_table + n); 227 228 /* Insert the root user immediately (init already runs as root) */ 229 spin_lock_irq(&uidhash_lock); 230 uid_hash_insert(&root_user, uidhashentry(GLOBAL_ROOT_UID)); 231 spin_unlock_irq(&uidhash_lock); 232 233 return 0; 234 } 235 subsys_initcall(uid_cache_init); 236