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/sched/user.h> 17 #include <linux/interrupt.h> 18 #include <linux/export.h> 19 #include <linux/user_namespace.h> 20 #include <linux/proc_ns.h> 21 22 /* 23 * userns count is 1 for root user, 1 for init_uts_ns, 24 * and 1 for... ? 25 */ 26 struct user_namespace init_user_ns = { 27 .uid_map = { 28 .nr_extents = 1, 29 .extent[0] = { 30 .first = 0, 31 .lower_first = 0, 32 .count = 4294967295U, 33 }, 34 }, 35 .gid_map = { 36 .nr_extents = 1, 37 .extent[0] = { 38 .first = 0, 39 .lower_first = 0, 40 .count = 4294967295U, 41 }, 42 }, 43 .projid_map = { 44 .nr_extents = 1, 45 .extent[0] = { 46 .first = 0, 47 .lower_first = 0, 48 .count = 4294967295U, 49 }, 50 }, 51 .count = ATOMIC_INIT(3), 52 .owner = GLOBAL_ROOT_UID, 53 .group = GLOBAL_ROOT_GID, 54 .ns.inum = PROC_USER_INIT_INO, 55 #ifdef CONFIG_USER_NS 56 .ns.ops = &userns_operations, 57 #endif 58 .flags = USERNS_INIT_FLAGS, 59 #ifdef CONFIG_PERSISTENT_KEYRINGS 60 .persistent_keyring_register_sem = 61 __RWSEM_INITIALIZER(init_user_ns.persistent_keyring_register_sem), 62 #endif 63 }; 64 EXPORT_SYMBOL_GPL(init_user_ns); 65 66 /* 67 * UID task count cache, to get fast user lookup in "alloc_uid" 68 * when changing user ID's (ie setuid() and friends). 69 */ 70 71 #define UIDHASH_BITS (CONFIG_BASE_SMALL ? 3 : 7) 72 #define UIDHASH_SZ (1 << UIDHASH_BITS) 73 #define UIDHASH_MASK (UIDHASH_SZ - 1) 74 #define __uidhashfn(uid) (((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK) 75 #define uidhashentry(uid) (uidhash_table + __uidhashfn((__kuid_val(uid)))) 76 77 static struct kmem_cache *uid_cachep; 78 struct hlist_head uidhash_table[UIDHASH_SZ]; 79 80 /* 81 * The uidhash_lock is mostly taken from process context, but it is 82 * occasionally also taken from softirq/tasklet context, when 83 * task-structs get RCU-freed. Hence all locking must be softirq-safe. 84 * But free_uid() is also called with local interrupts disabled, and running 85 * local_bh_enable() with local interrupts disabled is an error - we'll run 86 * softirq callbacks, and they can unconditionally enable interrupts, and 87 * the caller of free_uid() didn't expect that.. 88 */ 89 static DEFINE_SPINLOCK(uidhash_lock); 90 91 /* root_user.__count is 1, for init task cred */ 92 struct user_struct root_user = { 93 .__count = ATOMIC_INIT(1), 94 .processes = ATOMIC_INIT(1), 95 .sigpending = ATOMIC_INIT(0), 96 .locked_shm = 0, 97 .uid = GLOBAL_ROOT_UID, 98 }; 99 100 /* 101 * These routines must be called with the uidhash spinlock held! 102 */ 103 static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent) 104 { 105 hlist_add_head(&up->uidhash_node, hashent); 106 } 107 108 static void uid_hash_remove(struct user_struct *up) 109 { 110 hlist_del_init(&up->uidhash_node); 111 } 112 113 static struct user_struct *uid_hash_find(kuid_t uid, struct hlist_head *hashent) 114 { 115 struct user_struct *user; 116 117 hlist_for_each_entry(user, hashent, uidhash_node) { 118 if (uid_eq(user->uid, uid)) { 119 atomic_inc(&user->__count); 120 return user; 121 } 122 } 123 124 return NULL; 125 } 126 127 /* IRQs are disabled and uidhash_lock is held upon function entry. 128 * IRQ state (as stored in flags) is restored and uidhash_lock released 129 * upon function exit. 130 */ 131 static void free_user(struct user_struct *up, unsigned long flags) 132 __releases(&uidhash_lock) 133 { 134 uid_hash_remove(up); 135 spin_unlock_irqrestore(&uidhash_lock, flags); 136 key_put(up->uid_keyring); 137 key_put(up->session_keyring); 138 kmem_cache_free(uid_cachep, up); 139 } 140 141 /* 142 * Locate the user_struct for the passed UID. If found, take a ref on it. The 143 * caller must undo that ref with free_uid(). 144 * 145 * If the user_struct could not be found, return NULL. 146 */ 147 struct user_struct *find_user(kuid_t uid) 148 { 149 struct user_struct *ret; 150 unsigned long flags; 151 152 spin_lock_irqsave(&uidhash_lock, flags); 153 ret = uid_hash_find(uid, uidhashentry(uid)); 154 spin_unlock_irqrestore(&uidhash_lock, flags); 155 return ret; 156 } 157 158 void free_uid(struct user_struct *up) 159 { 160 unsigned long flags; 161 162 if (!up) 163 return; 164 165 local_irq_save(flags); 166 if (atomic_dec_and_lock(&up->__count, &uidhash_lock)) 167 free_user(up, flags); 168 else 169 local_irq_restore(flags); 170 } 171 172 struct user_struct *alloc_uid(kuid_t uid) 173 { 174 struct hlist_head *hashent = uidhashentry(uid); 175 struct user_struct *up, *new; 176 177 spin_lock_irq(&uidhash_lock); 178 up = uid_hash_find(uid, hashent); 179 spin_unlock_irq(&uidhash_lock); 180 181 if (!up) { 182 new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL); 183 if (!new) 184 goto out_unlock; 185 186 new->uid = uid; 187 atomic_set(&new->__count, 1); 188 189 /* 190 * Before adding this, check whether we raced 191 * on adding the same user already.. 192 */ 193 spin_lock_irq(&uidhash_lock); 194 up = uid_hash_find(uid, hashent); 195 if (up) { 196 key_put(new->uid_keyring); 197 key_put(new->session_keyring); 198 kmem_cache_free(uid_cachep, new); 199 } else { 200 uid_hash_insert(new, hashent); 201 up = new; 202 } 203 spin_unlock_irq(&uidhash_lock); 204 } 205 206 return up; 207 208 out_unlock: 209 return NULL; 210 } 211 212 static int __init uid_cache_init(void) 213 { 214 int n; 215 216 uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct), 217 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL); 218 219 for(n = 0; n < UIDHASH_SZ; ++n) 220 INIT_HLIST_HEAD(uidhash_table + n); 221 222 /* Insert the root user immediately (init already runs as root) */ 223 spin_lock_irq(&uidhash_lock); 224 uid_hash_insert(&root_user, uidhashentry(GLOBAL_ROOT_UID)); 225 spin_unlock_irq(&uidhash_lock); 226 227 return 0; 228 } 229 subsys_initcall(uid_cache_init); 230