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 .flags = USERNS_INIT_FLAGS, 58 #ifdef CONFIG_PERSISTENT_KEYRINGS 59 .persistent_keyring_register_sem = 60 __RWSEM_INITIALIZER(init_user_ns.persistent_keyring_register_sem), 61 #endif 62 }; 63 EXPORT_SYMBOL_GPL(init_user_ns); 64 65 /* 66 * UID task count cache, to get fast user lookup in "alloc_uid" 67 * when changing user ID's (ie setuid() and friends). 68 */ 69 70 #define UIDHASH_BITS (CONFIG_BASE_SMALL ? 3 : 7) 71 #define UIDHASH_SZ (1 << UIDHASH_BITS) 72 #define UIDHASH_MASK (UIDHASH_SZ - 1) 73 #define __uidhashfn(uid) (((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK) 74 #define uidhashentry(uid) (uidhash_table + __uidhashfn((__kuid_val(uid)))) 75 76 static struct kmem_cache *uid_cachep; 77 struct hlist_head uidhash_table[UIDHASH_SZ]; 78 79 /* 80 * The uidhash_lock is mostly taken from process context, but it is 81 * occasionally also taken from softirq/tasklet context, when 82 * task-structs get RCU-freed. Hence all locking must be softirq-safe. 83 * But free_uid() is also called with local interrupts disabled, and running 84 * local_bh_enable() with local interrupts disabled is an error - we'll run 85 * softirq callbacks, and they can unconditionally enable interrupts, and 86 * the caller of free_uid() didn't expect that.. 87 */ 88 static DEFINE_SPINLOCK(uidhash_lock); 89 90 /* root_user.__count is 1, for init task cred */ 91 struct user_struct root_user = { 92 .__count = ATOMIC_INIT(1), 93 .processes = ATOMIC_INIT(1), 94 .sigpending = ATOMIC_INIT(0), 95 .locked_shm = 0, 96 .uid = GLOBAL_ROOT_UID, 97 }; 98 99 /* 100 * These routines must be called with the uidhash spinlock held! 101 */ 102 static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent) 103 { 104 hlist_add_head(&up->uidhash_node, hashent); 105 } 106 107 static void uid_hash_remove(struct user_struct *up) 108 { 109 hlist_del_init(&up->uidhash_node); 110 } 111 112 static struct user_struct *uid_hash_find(kuid_t uid, struct hlist_head *hashent) 113 { 114 struct user_struct *user; 115 116 hlist_for_each_entry(user, hashent, uidhash_node) { 117 if (uid_eq(user->uid, uid)) { 118 atomic_inc(&user->__count); 119 return user; 120 } 121 } 122 123 return NULL; 124 } 125 126 /* IRQs are disabled and uidhash_lock is held upon function entry. 127 * IRQ state (as stored in flags) is restored and uidhash_lock released 128 * upon function exit. 129 */ 130 static void free_user(struct user_struct *up, unsigned long flags) 131 __releases(&uidhash_lock) 132 { 133 uid_hash_remove(up); 134 spin_unlock_irqrestore(&uidhash_lock, flags); 135 key_put(up->uid_keyring); 136 key_put(up->session_keyring); 137 kmem_cache_free(uid_cachep, up); 138 } 139 140 /* 141 * Locate the user_struct for the passed UID. If found, take a ref on it. The 142 * caller must undo that ref with free_uid(). 143 * 144 * If the user_struct could not be found, return NULL. 145 */ 146 struct user_struct *find_user(kuid_t uid) 147 { 148 struct user_struct *ret; 149 unsigned long flags; 150 151 spin_lock_irqsave(&uidhash_lock, flags); 152 ret = uid_hash_find(uid, uidhashentry(uid)); 153 spin_unlock_irqrestore(&uidhash_lock, flags); 154 return ret; 155 } 156 157 void free_uid(struct user_struct *up) 158 { 159 unsigned long flags; 160 161 if (!up) 162 return; 163 164 local_irq_save(flags); 165 if (atomic_dec_and_lock(&up->__count, &uidhash_lock)) 166 free_user(up, flags); 167 else 168 local_irq_restore(flags); 169 } 170 171 struct user_struct *alloc_uid(kuid_t uid) 172 { 173 struct hlist_head *hashent = uidhashentry(uid); 174 struct user_struct *up, *new; 175 176 spin_lock_irq(&uidhash_lock); 177 up = uid_hash_find(uid, hashent); 178 spin_unlock_irq(&uidhash_lock); 179 180 if (!up) { 181 new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL); 182 if (!new) 183 goto out_unlock; 184 185 new->uid = uid; 186 atomic_set(&new->__count, 1); 187 188 /* 189 * Before adding this, check whether we raced 190 * on adding the same user already.. 191 */ 192 spin_lock_irq(&uidhash_lock); 193 up = uid_hash_find(uid, hashent); 194 if (up) { 195 key_put(new->uid_keyring); 196 key_put(new->session_keyring); 197 kmem_cache_free(uid_cachep, new); 198 } else { 199 uid_hash_insert(new, hashent); 200 up = new; 201 } 202 spin_unlock_irq(&uidhash_lock); 203 } 204 205 return up; 206 207 out_unlock: 208 return NULL; 209 } 210 211 static int __init uid_cache_init(void) 212 { 213 int n; 214 215 uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct), 216 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL); 217 218 for(n = 0; n < UIDHASH_SZ; ++n) 219 INIT_HLIST_HEAD(uidhash_table + n); 220 221 /* Insert the root user immediately (init already runs as root) */ 222 spin_lock_irq(&uidhash_lock); 223 uid_hash_insert(&root_user, uidhashentry(GLOBAL_ROOT_UID)); 224 spin_unlock_irq(&uidhash_lock); 225 226 return 0; 227 } 228 subsys_initcall(uid_cache_init); 229