kernel/user.c

   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/module.h>
  18 #include <linux/user_namespace.h>
  19
  20 /*
  21  * UID task count cache, to get fast user lookup in "alloc_uid"
  22  * when changing user ID's (ie setuid() and friends).
  23  */
  24
  25 #define UIDHASH_MASK            (UIDHASH_SZ - 1)
  26 #define __uidhashfn(uid)        (((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK)
  27 #define uidhashentry(ns, uid)   ((ns)->uidhash_table + __uidhashfn((uid)))
  28
  29 static struct kmem_cache *uid_cachep;
  30
  31 /*
  32  * The uidhash_lock is mostly taken from process context, but it is
  33  * occasionally also taken from softirq/tasklet context, when
  34  * task-structs get RCU-freed. Hence all locking must be softirq-safe.
  35  * But free_uid() is also called with local interrupts disabled, and running
  36  * local_bh_enable() with local interrupts disabled is an error - we'll run
  37  * softirq callbacks, and they can unconditionally enable interrupts, and
  38  * the caller of free_uid() didn't expect that..
  39  */
  40 static DEFINE_SPINLOCK(uidhash_lock);
  41
  42 struct user_struct root_user = {
  43         .__count        = ATOMIC_INIT(1),
  44         .processes      = ATOMIC_INIT(1),
  45         .files          = ATOMIC_INIT(0),
  46         .sigpending     = ATOMIC_INIT(0),
  47         .locked_shm     = 0,
  48 #ifdef CONFIG_KEYS
  49         .uid_keyring    = &root_user_keyring,
  50         .session_keyring = &root_session_keyring,
  51 #endif
  52 #ifdef CONFIG_FAIR_USER_SCHED
  53         .tg             = &init_task_group,
  54 #endif
  55 };
  56
  57 /*
  58  * These routines must be called with the uidhash spinlock held!
  59  */
  60 static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent)
  61 {
  62         hlist_add_head(&up->uidhash_node, hashent);
  63 }
  64
  65 static void uid_hash_remove(struct user_struct *up)
  66 {
  67         hlist_del_init(&up->uidhash_node);
  68 }
  69
  70 static struct user_struct *uid_hash_find(uid_t uid, struct hlist_head *hashent)
  71 {
  72         struct user_struct *user;
  73         struct hlist_node *h;
  74
  75         hlist_for_each_entry(user, h, hashent, uidhash_node) {
  76                 if (user->uid == uid) {
  77                         atomic_inc(&user->__count);
  78                         return user;
  79                 }
  80         }
  81
  82         return NULL;
  83 }
  84
  85 #ifdef CONFIG_FAIR_USER_SCHED
  86
  87 static void sched_destroy_user(struct user_struct *up)
  88 {
  89         sched_destroy_group(up->tg);
  90 }
  91
  92 static int sched_create_user(struct user_struct *up)
  93 {
  94         int rc = 0;
  95
  96         up->tg = sched_create_group();
  97         if (IS_ERR(up->tg))
  98                 rc = -ENOMEM;
  99
 100         return rc;
 101 }
 102
 103 static void sched_switch_user(struct task_struct *p)
 104 {
 105         sched_move_task(p);
 106 }
 107
 108 #else   /* CONFIG_FAIR_USER_SCHED */
 109
 110 static void sched_destroy_user(struct user_struct *up) { }
 111 static int sched_create_user(struct user_struct *up) { return 0; }
 112 static void sched_switch_user(struct task_struct *p) { }
 113
 114 #endif  /* CONFIG_FAIR_USER_SCHED */
 115
 116 #if defined(CONFIG_FAIR_USER_SCHED) && defined(CONFIG_SYSFS)
 117
 118 static struct kset *uids_kset; /* represents the /sys/kernel/uids/ directory */
 119 static DEFINE_MUTEX(uids_mutex);
 120
 121 static inline void uids_mutex_lock(void)
 122 {
 123         mutex_lock(&uids_mutex);
 124 }
 125
 126 static inline void uids_mutex_unlock(void)
 127 {
 128         mutex_unlock(&uids_mutex);
 129 }
 130
 131 /* uid directory attributes */
 132 static ssize_t cpu_shares_show(struct kobject *kobj,
 133                                struct kobj_attribute *attr,
 134                                char *buf)
 135 {
 136         struct user_struct *up = container_of(kobj, struct user_struct, kobj);
 137
 138         return sprintf(buf, "%lu\n", sched_group_shares(up->tg));
 139 }
 140
 141 static ssize_t cpu_shares_store(struct kobject *kobj,
 142                                 struct kobj_attribute *attr,
 143                                 const char *buf, size_t size)
 144 {
 145         struct user_struct *up = container_of(kobj, struct user_struct, kobj);
 146         unsigned long shares;
 147         int rc;
 148
 149         sscanf(buf, "%lu", &shares);
 150
 151         rc = sched_group_set_shares(up->tg, shares);
 152
 153         return (rc ? rc : size);
 154 }
 155
 156 static struct kobj_attribute cpu_share_attr =
 157         __ATTR(cpu_share, 0644, cpu_shares_show, cpu_shares_store);
 158
 159 /* default attributes per uid directory */
 160 static struct attribute *uids_attributes[] = {
 161         &cpu_share_attr.attr,
 162         NULL
 163 };
 164
 165 /* the lifetime of user_struct is not managed by the core (now) */
 166 static void uids_release(struct kobject *kobj)
 167 {
 168         return;
 169 }
 170
 171 static struct kobj_type uids_ktype = {
 172         .sysfs_ops = &kobj_sysfs_ops,
 173         .default_attrs = uids_attributes,
 174         .release = uids_release,
 175 };
 176
 177 /* create /sys/kernel/uids/<uid>/cpu_share file for this user */
 178 static int uids_user_create(struct user_struct *up)
 179 {
 180         struct kobject *kobj = &up->kobj;
 181         int error;
 182
 183         memset(kobj, 0, sizeof(struct kobject));
 184         kobj->ktype = &uids_ktype;
 185         kobj->kset = uids_kset;
 186         kobject_init(kobj);
 187         kobject_set_name(&up->kobj, "%d", up->uid);
 188         error = kobject_add(kobj);
 189         if (error)
 190                 goto done;
 191
 192         kobject_uevent(kobj, KOBJ_ADD);
 193 done:
 194         return error;
 195 }
 196
 197 /* create these entries in sysfs:
 198  *      "/sys/kernel/uids" directory
 199  *      "/sys/kernel/uids/0" directory (for root user)
 200  *      "/sys/kernel/uids/0/cpu_share" file (for root user)
 201  */
 202 int __init uids_sysfs_init(void)
 203 {
 204         uids_kset = kset_create_and_add("uids", NULL, kernel_kobj);
 205         if (!uids_kset)
 206                 return -ENOMEM;
 207
 208         return uids_user_create(&root_user);
 209 }
 210
 211 /* work function to remove sysfs directory for a user and free up
 212  * corresponding structures.
 213  */
 214 static void remove_user_sysfs_dir(struct work_struct *w)
 215 {
 216         struct user_struct *up = container_of(w, struct user_struct, work);
 217         unsigned long flags;
 218         int remove_user = 0;
 219
 220         /* Make uid_hash_remove() + sysfs_remove_file() + kobject_del()
 221          * atomic.
 222          */
 223         uids_mutex_lock();
 224
 225         local_irq_save(flags);
 226
 227         if (atomic_dec_and_lock(&up->__count, &uidhash_lock)) {
 228                 uid_hash_remove(up);
 229                 remove_user = 1;
 230                 spin_unlock_irqrestore(&uidhash_lock, flags);
 231         } else {
 232                 local_irq_restore(flags);
 233         }
 234
 235         if (!remove_user)
 236                 goto done;
 237
 238         kobject_uevent(&up->kobj, KOBJ_REMOVE);
 239         kobject_del(&up->kobj);
 240         kobject_put(&up->kobj);
 241
 242         sched_destroy_user(up);
 243         key_put(up->uid_keyring);
 244         key_put(up->session_keyring);
 245         kmem_cache_free(uid_cachep, up);
 246
 247 done:
 248         uids_mutex_unlock();
 249 }
 250
 251 /* IRQs are disabled and uidhash_lock is held upon function entry.
 252  * IRQ state (as stored in flags) is restored and uidhash_lock released
 253  * upon function exit.
 254  */
 255 static inline void free_user(struct user_struct *up, unsigned long flags)
 256 {
 257         /* restore back the count */
 258         atomic_inc(&up->__count);
 259         spin_unlock_irqrestore(&uidhash_lock, flags);
 260
 261         INIT_WORK(&up->work, remove_user_sysfs_dir);
 262         schedule_work(&up->work);
 263 }
 264
 265 #else   /* CONFIG_FAIR_USER_SCHED && CONFIG_SYSFS */
 266
 267 int uids_sysfs_init(void) { return 0; }
 268 static inline int uids_user_create(struct user_struct *up) { return 0; }
 269 static inline void uids_mutex_lock(void) { }
 270 static inline void uids_mutex_unlock(void) { }
 271
 272 /* IRQs are disabled and uidhash_lock is held upon function entry.
 273  * IRQ state (as stored in flags) is restored and uidhash_lock released
 274  * upon function exit.
 275  */
 276 static inline void free_user(struct user_struct *up, unsigned long flags)
 277 {
 278         uid_hash_remove(up);
 279         spin_unlock_irqrestore(&uidhash_lock, flags);
 280         sched_destroy_user(up);
 281         key_put(up->uid_keyring);
 282         key_put(up->session_keyring);
 283         kmem_cache_free(uid_cachep, up);
 284 }
 285
 286 #endif
 287
 288 /*
 289  * Locate the user_struct for the passed UID.  If found, take a ref on it.  The
 290  * caller must undo that ref with free_uid().
 291  *
 292  * If the user_struct could not be found, return NULL.
 293  */
 294 struct user_struct *find_user(uid_t uid)
 295 {
 296         struct user_struct *ret;
 297         unsigned long flags;
 298         struct user_namespace *ns = current->nsproxy->user_ns;
 299
 300         spin_lock_irqsave(&uidhash_lock, flags);
 301         ret = uid_hash_find(uid, uidhashentry(ns, uid));
 302         spin_unlock_irqrestore(&uidhash_lock, flags);
 303         return ret;
 304 }
 305
 306 void free_uid(struct user_struct *up)
 307 {
 308         unsigned long flags;
 309
 310         if (!up)
 311                 return;
 312
 313         local_irq_save(flags);
 314         if (atomic_dec_and_lock(&up->__count, &uidhash_lock))
 315                 free_user(up, flags);
 316         else
 317                 local_irq_restore(flags);
 318 }
 319
 320 struct user_struct * alloc_uid(struct user_namespace *ns, uid_t uid)
 321 {
 322         struct hlist_head *hashent = uidhashentry(ns, uid);
 323         struct user_struct *up;
 324
 325         /* Make uid_hash_find() + uids_user_create() + uid_hash_insert()
 326          * atomic.
 327          */
 328         uids_mutex_lock();
 329
 330         spin_lock_irq(&uidhash_lock);
 331         up = uid_hash_find(uid, hashent);
 332         spin_unlock_irq(&uidhash_lock);
 333
 334         if (!up) {
 335                 struct user_struct *new;
 336
 337                 new = kmem_cache_alloc(uid_cachep, GFP_KERNEL);
 338                 if (!new) {
 339                         uids_mutex_unlock();
 340                         return NULL;
 341                 }
 342
 343                 new->uid = uid;
 344                 atomic_set(&new->__count, 1);
 345                 atomic_set(&new->processes, 0);
 346                 atomic_set(&new->files, 0);
 347                 atomic_set(&new->sigpending, 0);
 348 #ifdef CONFIG_INOTIFY_USER
 349                 atomic_set(&new->inotify_watches, 0);
 350                 atomic_set(&new->inotify_devs, 0);
 351 #endif
 352 #ifdef CONFIG_POSIX_MQUEUE
 353                 new->mq_bytes = 0;
 354 #endif
 355                 new->locked_shm = 0;
 356
 357                 if (alloc_uid_keyring(new, current) < 0) {
 358                         kmem_cache_free(uid_cachep, new);
 359                         uids_mutex_unlock();
 360                         return NULL;
 361                 }
 362
 363                 if (sched_create_user(new) < 0) {
 364                         key_put(new->uid_keyring);
 365                         key_put(new->session_keyring);
 366                         kmem_cache_free(uid_cachep, new);
 367                         uids_mutex_unlock();
 368                         return NULL;
 369                 }
 370
 371                 if (uids_user_create(new)) {
 372                         sched_destroy_user(new);
 373                         key_put(new->uid_keyring);
 374                         key_put(new->session_keyring);
 375                         kmem_cache_free(uid_cachep, new);
 376                         uids_mutex_unlock();
 377                         return NULL;
 378                 }
 379
 380                 /*
 381                  * Before adding this, check whether we raced
 382                  * on adding the same user already..
 383                  */
 384                 spin_lock_irq(&uidhash_lock);
 385                 up = uid_hash_find(uid, hashent);
 386                 if (up) {
 387                         /* This case is not possible when CONFIG_FAIR_USER_SCHED
 388                          * is defined, since we serialize alloc_uid() using
 389                          * uids_mutex. Hence no need to call
 390                          * sched_destroy_user() or remove_user_sysfs_dir().
 391                          */
 392                         key_put(new->uid_keyring);
 393                         key_put(new->session_keyring);
 394                         kmem_cache_free(uid_cachep, new);
 395                 } else {
 396                         uid_hash_insert(new, hashent);
 397                         up = new;
 398                 }
 399                 spin_unlock_irq(&uidhash_lock);
 400
 401         }
 402
 403         uids_mutex_unlock();
 404
 405         return up;
 406 }
 407
 408 void switch_uid(struct user_struct *new_user)
 409 {
 410         struct user_struct *old_user;
 411
 412         /* What if a process setreuid()'s and this brings the
 413          * new uid over his NPROC rlimit?  We can check this now
 414          * cheaply with the new uid cache, so if it matters
 415          * we should be checking for it.  -DaveM
 416          */
 417         old_user = current->user;
 418         atomic_inc(&new_user->processes);
 419         atomic_dec(&old_user->processes);
 420         switch_uid_keyring(new_user);
 421         current->user = new_user;
 422         sched_switch_user(current);
 423
 424         /*
 425          * We need to synchronize with __sigqueue_alloc()
 426          * doing a get_uid(p->user).. If that saw the old
 427          * user value, we need to wait until it has exited
 428          * its critical region before we can free the old
 429          * structure.
 430          */
 431         smp_mb();
 432         spin_unlock_wait(&current->sighand->siglock);
 433
 434         free_uid(old_user);
 435         suid_keys(current);
 436 }
 437
 438 void release_uids(struct user_namespace *ns)
 439 {
 440         int i;
 441         unsigned long flags;
 442         struct hlist_head *head;
 443         struct hlist_node *nd;
 444
 445         spin_lock_irqsave(&uidhash_lock, flags);
 446         /*
 447          * collapse the chains so that the user_struct-s will
 448          * be still alive, but not in hashes. subsequent free_uid()
 449          * will free them.
 450          */
 451         for (i = 0; i < UIDHASH_SZ; i++) {
 452                 head = ns->uidhash_table + i;
 453                 while (!hlist_empty(head)) {
 454                         nd = head->first;
 455                         hlist_del_init(nd);
 456                 }
 457         }
 458         spin_unlock_irqrestore(&uidhash_lock, flags);
 459
 460         free_uid(ns->root_user);
 461 }
 462
 463 static int __init uid_cache_init(void)
 464 {
 465         int n;
 466
 467         uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
 468                         0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
 469
 470         for(n = 0; n < UIDHASH_SZ; ++n)
 471                 INIT_HLIST_HEAD(init_user_ns.uidhash_table + n);
 472
 473         /* Insert the root user immediately (init already runs as root) */
 474         spin_lock_irq(&uidhash_lock);
 475         uid_hash_insert(&root_user, uidhashentry(&init_user_ns, 0));
 476         spin_unlock_irq(&uidhash_lock);
 477
 478         return 0;
 479 }
 480
 481 module_init(uid_cache_init);