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 .kref = { 26 .refcount = ATOMIC_INIT(3), 27 }, 28 .creator = &root_user, 29 }; 30 EXPORT_SYMBOL_GPL(init_user_ns); 31 32 /* 33 * UID task count cache, to get fast user lookup in "alloc_uid" 34 * when changing user ID's (ie setuid() and friends). 35 */ 36 37 #define UIDHASH_MASK (UIDHASH_SZ - 1) 38 #define __uidhashfn(uid) (((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK) 39 #define uidhashentry(ns, uid) ((ns)->uidhash_table + __uidhashfn((uid))) 40 41 static struct kmem_cache *uid_cachep; 42 43 /* 44 * The uidhash_lock is mostly taken from process context, but it is 45 * occasionally also taken from softirq/tasklet context, when 46 * task-structs get RCU-freed. Hence all locking must be softirq-safe. 47 * But free_uid() is also called with local interrupts disabled, and running 48 * local_bh_enable() with local interrupts disabled is an error - we'll run 49 * softirq callbacks, and they can unconditionally enable interrupts, and 50 * the caller of free_uid() didn't expect that.. 51 */ 52 static DEFINE_SPINLOCK(uidhash_lock); 53 54 /* root_user.__count is 2, 1 for init task cred, 1 for init_user_ns->user_ns */ 55 struct user_struct root_user = { 56 .__count = ATOMIC_INIT(2), 57 .processes = ATOMIC_INIT(1), 58 .files = ATOMIC_INIT(0), 59 .sigpending = ATOMIC_INIT(0), 60 .locked_shm = 0, 61 .user_ns = &init_user_ns, 62 }; 63 64 /* 65 * These routines must be called with the uidhash spinlock held! 66 */ 67 static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent) 68 { 69 hlist_add_head(&up->uidhash_node, hashent); 70 } 71 72 static void uid_hash_remove(struct user_struct *up) 73 { 74 hlist_del_init(&up->uidhash_node); 75 put_user_ns(up->user_ns); 76 } 77 78 static struct user_struct *uid_hash_find(uid_t uid, struct hlist_head *hashent) 79 { 80 struct user_struct *user; 81 struct hlist_node *h; 82 83 hlist_for_each_entry(user, h, hashent, uidhash_node) { 84 if (user->uid == uid) { 85 atomic_inc(&user->__count); 86 return user; 87 } 88 } 89 90 return NULL; 91 } 92 93 /* IRQs are disabled and uidhash_lock is held upon function entry. 94 * IRQ state (as stored in flags) is restored and uidhash_lock released 95 * upon function exit. 96 */ 97 static void free_user(struct user_struct *up, unsigned long flags) 98 __releases(&uidhash_lock) 99 { 100 uid_hash_remove(up); 101 spin_unlock_irqrestore(&uidhash_lock, flags); 102 key_put(up->uid_keyring); 103 key_put(up->session_keyring); 104 kmem_cache_free(uid_cachep, up); 105 } 106 107 /* 108 * Locate the user_struct for the passed UID. If found, take a ref on it. The 109 * caller must undo that ref with free_uid(). 110 * 111 * If the user_struct could not be found, return NULL. 112 */ 113 struct user_struct *find_user(uid_t uid) 114 { 115 struct user_struct *ret; 116 unsigned long flags; 117 struct user_namespace *ns = current_user_ns(); 118 119 spin_lock_irqsave(&uidhash_lock, flags); 120 ret = uid_hash_find(uid, uidhashentry(ns, uid)); 121 spin_unlock_irqrestore(&uidhash_lock, flags); 122 return ret; 123 } 124 125 void free_uid(struct user_struct *up) 126 { 127 unsigned long flags; 128 129 if (!up) 130 return; 131 132 local_irq_save(flags); 133 if (atomic_dec_and_lock(&up->__count, &uidhash_lock)) 134 free_user(up, flags); 135 else 136 local_irq_restore(flags); 137 } 138 139 struct user_struct *alloc_uid(struct user_namespace *ns, uid_t uid) 140 { 141 struct hlist_head *hashent = uidhashentry(ns, uid); 142 struct user_struct *up, *new; 143 144 spin_lock_irq(&uidhash_lock); 145 up = uid_hash_find(uid, hashent); 146 spin_unlock_irq(&uidhash_lock); 147 148 if (!up) { 149 new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL); 150 if (!new) 151 goto out_unlock; 152 153 new->uid = uid; 154 atomic_set(&new->__count, 1); 155 156 new->user_ns = get_user_ns(ns); 157 158 /* 159 * Before adding this, check whether we raced 160 * on adding the same user already.. 161 */ 162 spin_lock_irq(&uidhash_lock); 163 up = uid_hash_find(uid, hashent); 164 if (up) { 165 put_user_ns(ns); 166 key_put(new->uid_keyring); 167 key_put(new->session_keyring); 168 kmem_cache_free(uid_cachep, new); 169 } else { 170 uid_hash_insert(new, hashent); 171 up = new; 172 } 173 spin_unlock_irq(&uidhash_lock); 174 } 175 176 return up; 177 178 out_unlock: 179 return NULL; 180 } 181 182 static int __init uid_cache_init(void) 183 { 184 int n; 185 186 uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct), 187 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL); 188 189 for(n = 0; n < UIDHASH_SZ; ++n) 190 INIT_HLIST_HEAD(init_user_ns.uidhash_table + n); 191 192 /* Insert the root user immediately (init already runs as root) */ 193 spin_lock_irq(&uidhash_lock); 194 uid_hash_insert(&root_user, uidhashentry(&init_user_ns, 0)); 195 spin_unlock_irq(&uidhash_lock); 196 197 return 0; 198 } 199 200 module_init(uid_cache_init); 201