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 .proc_inum = PROC_USER_INIT_INO, 54 #ifdef CONFIG_PERSISTENT_KEYRINGS 55 .persistent_keyring_register_sem = 56 __RWSEM_INITIALIZER(init_user_ns.persistent_keyring_register_sem), 57 #endif 58 }; 59 EXPORT_SYMBOL_GPL(init_user_ns); 60 61 /* 62 * UID task count cache, to get fast user lookup in "alloc_uid" 63 * when changing user ID's (ie setuid() and friends). 64 */ 65 66 #define UIDHASH_BITS (CONFIG_BASE_SMALL ? 3 : 7) 67 #define UIDHASH_SZ (1 << UIDHASH_BITS) 68 #define UIDHASH_MASK (UIDHASH_SZ - 1) 69 #define __uidhashfn(uid) (((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK) 70 #define uidhashentry(uid) (uidhash_table + __uidhashfn((__kuid_val(uid)))) 71 72 static struct kmem_cache *uid_cachep; 73 struct hlist_head uidhash_table[UIDHASH_SZ]; 74 75 /* 76 * The uidhash_lock is mostly taken from process context, but it is 77 * occasionally also taken from softirq/tasklet context, when 78 * task-structs get RCU-freed. Hence all locking must be softirq-safe. 79 * But free_uid() is also called with local interrupts disabled, and running 80 * local_bh_enable() with local interrupts disabled is an error - we'll run 81 * softirq callbacks, and they can unconditionally enable interrupts, and 82 * the caller of free_uid() didn't expect that.. 83 */ 84 static DEFINE_SPINLOCK(uidhash_lock); 85 86 /* root_user.__count is 1, for init task cred */ 87 struct user_struct root_user = { 88 .__count = ATOMIC_INIT(1), 89 .processes = ATOMIC_INIT(1), 90 .files = ATOMIC_INIT(0), 91 .sigpending = ATOMIC_INIT(0), 92 .locked_shm = 0, 93 .uid = GLOBAL_ROOT_UID, 94 }; 95 96 /* 97 * These routines must be called with the uidhash spinlock held! 98 */ 99 static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent) 100 { 101 hlist_add_head(&up->uidhash_node, hashent); 102 } 103 104 static void uid_hash_remove(struct user_struct *up) 105 { 106 hlist_del_init(&up->uidhash_node); 107 } 108 109 static struct user_struct *uid_hash_find(kuid_t uid, struct hlist_head *hashent) 110 { 111 struct user_struct *user; 112 113 hlist_for_each_entry(user, hashent, uidhash_node) { 114 if (uid_eq(user->uid, uid)) { 115 atomic_inc(&user->__count); 116 return user; 117 } 118 } 119 120 return NULL; 121 } 122 123 /* IRQs are disabled and uidhash_lock is held upon function entry. 124 * IRQ state (as stored in flags) is restored and uidhash_lock released 125 * upon function exit. 126 */ 127 static void free_user(struct user_struct *up, unsigned long flags) 128 __releases(&uidhash_lock) 129 { 130 uid_hash_remove(up); 131 spin_unlock_irqrestore(&uidhash_lock, flags); 132 key_put(up->uid_keyring); 133 key_put(up->session_keyring); 134 kmem_cache_free(uid_cachep, up); 135 } 136 137 /* 138 * Locate the user_struct for the passed UID. If found, take a ref on it. The 139 * caller must undo that ref with free_uid(). 140 * 141 * If the user_struct could not be found, return NULL. 142 */ 143 struct user_struct *find_user(kuid_t uid) 144 { 145 struct user_struct *ret; 146 unsigned long flags; 147 148 spin_lock_irqsave(&uidhash_lock, flags); 149 ret = uid_hash_find(uid, uidhashentry(uid)); 150 spin_unlock_irqrestore(&uidhash_lock, flags); 151 return ret; 152 } 153 154 void free_uid(struct user_struct *up) 155 { 156 unsigned long flags; 157 158 if (!up) 159 return; 160 161 local_irq_save(flags); 162 if (atomic_dec_and_lock(&up->__count, &uidhash_lock)) 163 free_user(up, flags); 164 else 165 local_irq_restore(flags); 166 } 167 168 struct user_struct *alloc_uid(kuid_t uid) 169 { 170 struct hlist_head *hashent = uidhashentry(uid); 171 struct user_struct *up, *new; 172 173 spin_lock_irq(&uidhash_lock); 174 up = uid_hash_find(uid, hashent); 175 spin_unlock_irq(&uidhash_lock); 176 177 if (!up) { 178 new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL); 179 if (!new) 180 goto out_unlock; 181 182 new->uid = uid; 183 atomic_set(&new->__count, 1); 184 185 /* 186 * Before adding this, check whether we raced 187 * on adding the same user already.. 188 */ 189 spin_lock_irq(&uidhash_lock); 190 up = uid_hash_find(uid, hashent); 191 if (up) { 192 key_put(new->uid_keyring); 193 key_put(new->session_keyring); 194 kmem_cache_free(uid_cachep, new); 195 } else { 196 uid_hash_insert(new, hashent); 197 up = new; 198 } 199 spin_unlock_irq(&uidhash_lock); 200 } 201 202 return up; 203 204 out_unlock: 205 return NULL; 206 } 207 208 static int __init uid_cache_init(void) 209 { 210 int n; 211 212 uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct), 213 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL); 214 215 for(n = 0; n < UIDHASH_SZ; ++n) 216 INIT_HLIST_HEAD(uidhash_table + n); 217 218 /* Insert the root user immediately (init already runs as root) */ 219 spin_lock_irq(&uidhash_lock); 220 uid_hash_insert(&root_user, uidhashentry(GLOBAL_ROOT_UID)); 221 spin_unlock_irq(&uidhash_lock); 222 223 return 0; 224 } 225 226 module_init(uid_cache_init); 227