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 .sigpending = ATOMIC_INIT(0), 91 .locked_shm = 0, 92 .uid = GLOBAL_ROOT_UID, 93 }; 94 95 /* 96 * These routines must be called with the uidhash spinlock held! 97 */ 98 static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent) 99 { 100 hlist_add_head(&up->uidhash_node, hashent); 101 } 102 103 static void uid_hash_remove(struct user_struct *up) 104 { 105 hlist_del_init(&up->uidhash_node); 106 } 107 108 static struct user_struct *uid_hash_find(kuid_t uid, struct hlist_head *hashent) 109 { 110 struct user_struct *user; 111 112 hlist_for_each_entry(user, hashent, uidhash_node) { 113 if (uid_eq(user->uid, uid)) { 114 atomic_inc(&user->__count); 115 return user; 116 } 117 } 118 119 return NULL; 120 } 121 122 /* IRQs are disabled and uidhash_lock is held upon function entry. 123 * IRQ state (as stored in flags) is restored and uidhash_lock released 124 * upon function exit. 125 */ 126 static void free_user(struct user_struct *up, unsigned long flags) 127 __releases(&uidhash_lock) 128 { 129 uid_hash_remove(up); 130 spin_unlock_irqrestore(&uidhash_lock, flags); 131 key_put(up->uid_keyring); 132 key_put(up->session_keyring); 133 kmem_cache_free(uid_cachep, up); 134 } 135 136 /* 137 * Locate the user_struct for the passed UID. If found, take a ref on it. The 138 * caller must undo that ref with free_uid(). 139 * 140 * If the user_struct could not be found, return NULL. 141 */ 142 struct user_struct *find_user(kuid_t uid) 143 { 144 struct user_struct *ret; 145 unsigned long flags; 146 147 spin_lock_irqsave(&uidhash_lock, flags); 148 ret = uid_hash_find(uid, uidhashentry(uid)); 149 spin_unlock_irqrestore(&uidhash_lock, flags); 150 return ret; 151 } 152 153 void free_uid(struct user_struct *up) 154 { 155 unsigned long flags; 156 157 if (!up) 158 return; 159 160 local_irq_save(flags); 161 if (atomic_dec_and_lock(&up->__count, &uidhash_lock)) 162 free_user(up, flags); 163 else 164 local_irq_restore(flags); 165 } 166 167 struct user_struct *alloc_uid(kuid_t uid) 168 { 169 struct hlist_head *hashent = uidhashentry(uid); 170 struct user_struct *up, *new; 171 172 spin_lock_irq(&uidhash_lock); 173 up = uid_hash_find(uid, hashent); 174 spin_unlock_irq(&uidhash_lock); 175 176 if (!up) { 177 new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL); 178 if (!new) 179 goto out_unlock; 180 181 new->uid = uid; 182 atomic_set(&new->__count, 1); 183 184 /* 185 * Before adding this, check whether we raced 186 * on adding the same user already.. 187 */ 188 spin_lock_irq(&uidhash_lock); 189 up = uid_hash_find(uid, hashent); 190 if (up) { 191 key_put(new->uid_keyring); 192 key_put(new->session_keyring); 193 kmem_cache_free(uid_cachep, new); 194 } else { 195 uid_hash_insert(new, hashent); 196 up = new; 197 } 198 spin_unlock_irq(&uidhash_lock); 199 } 200 201 return up; 202 203 out_unlock: 204 return NULL; 205 } 206 207 static int __init uid_cache_init(void) 208 { 209 int n; 210 211 uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct), 212 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL); 213 214 for(n = 0; n < UIDHASH_SZ; ++n) 215 INIT_HLIST_HEAD(uidhash_table + n); 216 217 /* Insert the root user immediately (init already runs as root) */ 218 spin_lock_irq(&uidhash_lock); 219 uid_hash_insert(&root_user, uidhashentry(GLOBAL_ROOT_UID)); 220 spin_unlock_irq(&uidhash_lock); 221 222 return 0; 223 } 224 subsys_initcall(uid_cache_init); 225