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/interrupt.h> 17 #include <linux/export.h> 18 #include <linux/user_namespace.h> 19 #include <linux/proc_ns.h> 20 21 /* 22 * userns count is 1 for root user, 1 for init_uts_ns, 23 * and 1 for... ? 24 */ 25 struct user_namespace init_user_ns = { 26 .uid_map = { 27 .nr_extents = 1, 28 .extent[0] = { 29 .first = 0, 30 .lower_first = 0, 31 .count = 4294967295U, 32 }, 33 }, 34 .gid_map = { 35 .nr_extents = 1, 36 .extent[0] = { 37 .first = 0, 38 .lower_first = 0, 39 .count = 4294967295U, 40 }, 41 }, 42 .projid_map = { 43 .nr_extents = 1, 44 .extent[0] = { 45 .first = 0, 46 .lower_first = 0, 47 .count = 4294967295U, 48 }, 49 }, 50 .count = ATOMIC_INIT(3), 51 .owner = GLOBAL_ROOT_UID, 52 .group = GLOBAL_ROOT_GID, 53 .ns.inum = PROC_USER_INIT_INO, 54 #ifdef CONFIG_USER_NS 55 .ns.ops = &userns_operations, 56 #endif 57 #ifdef CONFIG_PERSISTENT_KEYRINGS 58 .persistent_keyring_register_sem = 59 __RWSEM_INITIALIZER(init_user_ns.persistent_keyring_register_sem), 60 #endif 61 }; 62 EXPORT_SYMBOL_GPL(init_user_ns); 63 64 /* 65 * UID task count cache, to get fast user lookup in "alloc_uid" 66 * when changing user ID's (ie setuid() and friends). 67 */ 68 69 #define UIDHASH_BITS (CONFIG_BASE_SMALL ? 3 : 7) 70 #define UIDHASH_SZ (1 << UIDHASH_BITS) 71 #define UIDHASH_MASK (UIDHASH_SZ - 1) 72 #define __uidhashfn(uid) (((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK) 73 #define uidhashentry(uid) (uidhash_table + __uidhashfn((__kuid_val(uid)))) 74 75 static struct kmem_cache *uid_cachep; 76 struct hlist_head uidhash_table[UIDHASH_SZ]; 77 78 /* 79 * The uidhash_lock is mostly taken from process context, but it is 80 * occasionally also taken from softirq/tasklet context, when 81 * task-structs get RCU-freed. Hence all locking must be softirq-safe. 82 * But free_uid() is also called with local interrupts disabled, and running 83 * local_bh_enable() with local interrupts disabled is an error - we'll run 84 * softirq callbacks, and they can unconditionally enable interrupts, and 85 * the caller of free_uid() didn't expect that.. 86 */ 87 static DEFINE_SPINLOCK(uidhash_lock); 88 89 /* root_user.__count is 1, for init task cred */ 90 struct user_struct root_user = { 91 .__count = ATOMIC_INIT(1), 92 .processes = ATOMIC_INIT(1), 93 .sigpending = ATOMIC_INIT(0), 94 .locked_shm = 0, 95 .uid = GLOBAL_ROOT_UID, 96 }; 97 98 /* 99 * These routines must be called with the uidhash spinlock held! 100 */ 101 static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent) 102 { 103 hlist_add_head(&up->uidhash_node, hashent); 104 } 105 106 static void uid_hash_remove(struct user_struct *up) 107 { 108 hlist_del_init(&up->uidhash_node); 109 } 110 111 static struct user_struct *uid_hash_find(kuid_t uid, struct hlist_head *hashent) 112 { 113 struct user_struct *user; 114 115 hlist_for_each_entry(user, hashent, uidhash_node) { 116 if (uid_eq(user->uid, uid)) { 117 atomic_inc(&user->__count); 118 return user; 119 } 120 } 121 122 return NULL; 123 } 124 125 /* IRQs are disabled and uidhash_lock is held upon function entry. 126 * IRQ state (as stored in flags) is restored and uidhash_lock released 127 * upon function exit. 128 */ 129 static void free_user(struct user_struct *up, unsigned long flags) 130 __releases(&uidhash_lock) 131 { 132 uid_hash_remove(up); 133 spin_unlock_irqrestore(&uidhash_lock, flags); 134 key_put(up->uid_keyring); 135 key_put(up->session_keyring); 136 kmem_cache_free(uid_cachep, up); 137 } 138 139 /* 140 * Locate the user_struct for the passed UID. If found, take a ref on it. The 141 * caller must undo that ref with free_uid(). 142 * 143 * If the user_struct could not be found, return NULL. 144 */ 145 struct user_struct *find_user(kuid_t uid) 146 { 147 struct user_struct *ret; 148 unsigned long flags; 149 150 spin_lock_irqsave(&uidhash_lock, flags); 151 ret = uid_hash_find(uid, uidhashentry(uid)); 152 spin_unlock_irqrestore(&uidhash_lock, flags); 153 return ret; 154 } 155 156 void free_uid(struct user_struct *up) 157 { 158 unsigned long flags; 159 160 if (!up) 161 return; 162 163 local_irq_save(flags); 164 if (atomic_dec_and_lock(&up->__count, &uidhash_lock)) 165 free_user(up, flags); 166 else 167 local_irq_restore(flags); 168 } 169 170 struct user_struct *alloc_uid(kuid_t uid) 171 { 172 struct hlist_head *hashent = uidhashentry(uid); 173 struct user_struct *up, *new; 174 175 spin_lock_irq(&uidhash_lock); 176 up = uid_hash_find(uid, hashent); 177 spin_unlock_irq(&uidhash_lock); 178 179 if (!up) { 180 new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL); 181 if (!new) 182 goto out_unlock; 183 184 new->uid = uid; 185 atomic_set(&new->__count, 1); 186 187 /* 188 * Before adding this, check whether we raced 189 * on adding the same user already.. 190 */ 191 spin_lock_irq(&uidhash_lock); 192 up = uid_hash_find(uid, hashent); 193 if (up) { 194 key_put(new->uid_keyring); 195 key_put(new->session_keyring); 196 kmem_cache_free(uid_cachep, new); 197 } else { 198 uid_hash_insert(new, hashent); 199 up = new; 200 } 201 spin_unlock_irq(&uidhash_lock); 202 } 203 204 return up; 205 206 out_unlock: 207 return NULL; 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