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