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 20 /* 21 * userns count is 1 for root user, 1 for init_uts_ns, 22 * and 1 for... ? 23 */ 24 struct user_namespace init_user_ns = { 25 .uid_map = { 26 .nr_extents = 1, 27 .extent[0] = { 28 .first = 0, 29 .lower_first = 0, 30 .count = 4294967295U, 31 }, 32 }, 33 .gid_map = { 34 .nr_extents = 1, 35 .extent[0] = { 36 .first = 0, 37 .lower_first = 0, 38 .count = 4294967295U, 39 }, 40 }, 41 .projid_map = { 42 .nr_extents = 1, 43 .extent[0] = { 44 .first = 0, 45 .lower_first = 0, 46 .count = 4294967295U, 47 }, 48 }, 49 .kref = { 50 .refcount = ATOMIC_INIT(3), 51 }, 52 .owner = GLOBAL_ROOT_UID, 53 .group = GLOBAL_ROOT_GID, 54 }; 55 EXPORT_SYMBOL_GPL(init_user_ns); 56 57 /* 58 * UID task count cache, to get fast user lookup in "alloc_uid" 59 * when changing user ID's (ie setuid() and friends). 60 */ 61 62 #define UIDHASH_BITS (CONFIG_BASE_SMALL ? 3 : 7) 63 #define UIDHASH_SZ (1 << UIDHASH_BITS) 64 #define UIDHASH_MASK (UIDHASH_SZ - 1) 65 #define __uidhashfn(uid) (((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK) 66 #define uidhashentry(uid) (uidhash_table + __uidhashfn((__kuid_val(uid)))) 67 68 static struct kmem_cache *uid_cachep; 69 struct hlist_head uidhash_table[UIDHASH_SZ]; 70 71 /* 72 * The uidhash_lock is mostly taken from process context, but it is 73 * occasionally also taken from softirq/tasklet context, when 74 * task-structs get RCU-freed. Hence all locking must be softirq-safe. 75 * But free_uid() is also called with local interrupts disabled, and running 76 * local_bh_enable() with local interrupts disabled is an error - we'll run 77 * softirq callbacks, and they can unconditionally enable interrupts, and 78 * the caller of free_uid() didn't expect that.. 79 */ 80 static DEFINE_SPINLOCK(uidhash_lock); 81 82 /* root_user.__count is 1, for init task cred */ 83 struct user_struct root_user = { 84 .__count = ATOMIC_INIT(1), 85 .processes = ATOMIC_INIT(1), 86 .files = ATOMIC_INIT(0), 87 .sigpending = ATOMIC_INIT(0), 88 .locked_shm = 0, 89 .uid = GLOBAL_ROOT_UID, 90 }; 91 92 /* 93 * These routines must be called with the uidhash spinlock held! 94 */ 95 static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent) 96 { 97 hlist_add_head(&up->uidhash_node, hashent); 98 } 99 100 static void uid_hash_remove(struct user_struct *up) 101 { 102 hlist_del_init(&up->uidhash_node); 103 } 104 105 static struct user_struct *uid_hash_find(kuid_t uid, struct hlist_head *hashent) 106 { 107 struct user_struct *user; 108 struct hlist_node *h; 109 110 hlist_for_each_entry(user, h, hashent, uidhash_node) { 111 if (uid_eq(user->uid, uid)) { 112 atomic_inc(&user->__count); 113 return user; 114 } 115 } 116 117 return NULL; 118 } 119 120 /* IRQs are disabled and uidhash_lock is held upon function entry. 121 * IRQ state (as stored in flags) is restored and uidhash_lock released 122 * upon function exit. 123 */ 124 static void free_user(struct user_struct *up, unsigned long flags) 125 __releases(&uidhash_lock) 126 { 127 uid_hash_remove(up); 128 spin_unlock_irqrestore(&uidhash_lock, flags); 129 key_put(up->uid_keyring); 130 key_put(up->session_keyring); 131 kmem_cache_free(uid_cachep, up); 132 } 133 134 /* 135 * Locate the user_struct for the passed UID. If found, take a ref on it. The 136 * caller must undo that ref with free_uid(). 137 * 138 * If the user_struct could not be found, return NULL. 139 */ 140 struct user_struct *find_user(kuid_t uid) 141 { 142 struct user_struct *ret; 143 unsigned long flags; 144 145 spin_lock_irqsave(&uidhash_lock, flags); 146 ret = uid_hash_find(uid, uidhashentry(uid)); 147 spin_unlock_irqrestore(&uidhash_lock, flags); 148 return ret; 149 } 150 151 void free_uid(struct user_struct *up) 152 { 153 unsigned long flags; 154 155 if (!up) 156 return; 157 158 local_irq_save(flags); 159 if (atomic_dec_and_lock(&up->__count, &uidhash_lock)) 160 free_user(up, flags); 161 else 162 local_irq_restore(flags); 163 } 164 165 struct user_struct *alloc_uid(kuid_t uid) 166 { 167 struct hlist_head *hashent = uidhashentry(uid); 168 struct user_struct *up, *new; 169 170 spin_lock_irq(&uidhash_lock); 171 up = uid_hash_find(uid, hashent); 172 spin_unlock_irq(&uidhash_lock); 173 174 if (!up) { 175 new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL); 176 if (!new) 177 goto out_unlock; 178 179 new->uid = uid; 180 atomic_set(&new->__count, 1); 181 182 /* 183 * Before adding this, check whether we raced 184 * on adding the same user already.. 185 */ 186 spin_lock_irq(&uidhash_lock); 187 up = uid_hash_find(uid, hashent); 188 if (up) { 189 key_put(new->uid_keyring); 190 key_put(new->session_keyring); 191 kmem_cache_free(uid_cachep, new); 192 } else { 193 uid_hash_insert(new, hashent); 194 up = new; 195 } 196 spin_unlock_irq(&uidhash_lock); 197 } 198 199 return up; 200 201 out_unlock: 202 return NULL; 203 } 204 205 static int __init uid_cache_init(void) 206 { 207 int n; 208 209 uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct), 210 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL); 211 212 for(n = 0; n < UIDHASH_SZ; ++n) 213 INIT_HLIST_HEAD(uidhash_table + n); 214 215 /* Insert the root user immediately (init already runs as root) */ 216 spin_lock_irq(&uidhash_lock); 217 uid_hash_insert(&root_user, uidhashentry(GLOBAL_ROOT_UID)); 218 spin_unlock_irq(&uidhash_lock); 219 220 return 0; 221 } 222 223 module_init(uid_cache_init); 224