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