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 struct user_namespace init_user_ns = {
  21         .kref = {
  22                 .refcount       = ATOMIC_INIT(2),
  23         },
  24         .root_user = &root_user,
  25 };
  26 EXPORT_SYMBOL_GPL(init_user_ns);
  27
  28 /*
  29  * UID task count cache, to get fast user lookup in "alloc_uid"
  30  * when changing user ID's (ie setuid() and friends).
  31  */
  32
  33 #define UIDHASH_MASK            (UIDHASH_SZ - 1)
  34 #define __uidhashfn(uid)        (((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK)
  35 #define uidhashentry(ns, uid)   ((ns)->uidhash_table + __uidhashfn((uid)))
  36
  37 static struct kmem_cache *uid_cachep;
  38
  39 /*
  40  * The uidhash_lock is mostly taken from process context, but it is
  41  * occasionally also taken from softirq/tasklet context, when
  42  * task-structs get RCU-freed. Hence all locking must be softirq-safe.
  43  * But free_uid() is also called with local interrupts disabled, and running
  44  * local_bh_enable() with local interrupts disabled is an error - we'll run
  45  * softirq callbacks, and they can unconditionally enable interrupts, and
  46  * the caller of free_uid() didn't expect that..
  47  */
  48 static DEFINE_SPINLOCK(uidhash_lock);
  49
  50 struct user_struct root_user = {
  51         .__count        = ATOMIC_INIT(1),
  52         .processes      = ATOMIC_INIT(1),
  53         .files          = ATOMIC_INIT(0),
  54         .sigpending     = ATOMIC_INIT(0),
  55         .locked_shm     = 0,
  56 #ifdef CONFIG_KEYS
  57         .uid_keyring    = &root_user_keyring,
  58         .session_keyring = &root_session_keyring,
  59 #endif
  60 #ifdef CONFIG_FAIR_USER_SCHED
  61         .tg             = &init_task_group,
  62 #endif
  63 };
  64
  65 /*
  66  * These routines must be called with the uidhash spinlock held!
  67  */
  68 static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent)
  69 {
  70         hlist_add_head(&up->uidhash_node, hashent);
  71 }
  72
  73 static void uid_hash_remove(struct user_struct *up)
  74 {
  75         hlist_del_init(&up->uidhash_node);
  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 #ifdef CONFIG_FAIR_USER_SCHED
  94
  95 static void sched_destroy_user(struct user_struct *up)
  96 {
  97         sched_destroy_group(up->tg);
  98 }
  99
 100 static int sched_create_user(struct user_struct *up)
 101 {
 102         int rc = 0;
 103
 104         up->tg = sched_create_group();
 105         if (IS_ERR(up->tg))
 106                 rc = -ENOMEM;
 107
 108         return rc;
 109 }
 110
 111 static void sched_switch_user(struct task_struct *p)
 112 {
 113         sched_move_task(p);
 114 }
 115
 116 #else   /* CONFIG_FAIR_USER_SCHED */
 117
 118 static void sched_destroy_user(struct user_struct *up) { }
 119 static int sched_create_user(struct user_struct *up) { return 0; }
 120 static void sched_switch_user(struct task_struct *p) { }
 121
 122 #endif  /* CONFIG_FAIR_USER_SCHED */
 123
 124 #if defined(CONFIG_FAIR_USER_SCHED) && defined(CONFIG_SYSFS)
 125
 126 static struct kset *uids_kset; /* represents the /sys/kernel/uids/ directory */
 127 static DEFINE_MUTEX(uids_mutex);
 128
 129 static inline void uids_mutex_lock(void)
 130 {
 131         mutex_lock(&uids_mutex);
 132 }
 133
 134 static inline void uids_mutex_unlock(void)
 135 {
 136         mutex_unlock(&uids_mutex);
 137 }
 138
 139 /* uid directory attributes */
 140 static ssize_t cpu_shares_show(struct kobject *kobj,
 141                                struct kobj_attribute *attr,
 142                                char *buf)
 143 {
 144         struct user_struct *up = container_of(kobj, struct user_struct, kobj);
 145
 146         return sprintf(buf, "%lu\n", sched_group_shares(up->tg));
 147 }
 148
 149 static ssize_t cpu_shares_store(struct kobject *kobj,
 150                                 struct kobj_attribute *attr,
 151                                 const char *buf, size_t size)
 152 {
 153         struct user_struct *up = container_of(kobj, struct user_struct, kobj);
 154         unsigned long shares;
 155         int rc;
 156
 157         sscanf(buf, "%lu", &shares);
 158
 159         rc = sched_group_set_shares(up->tg, shares);
 160
 161         return (rc ? rc : size);
 162 }
 163
 164 static struct kobj_attribute cpu_share_attr =
 165         __ATTR(cpu_share, 0644, cpu_shares_show, cpu_shares_store);
 166
 167 static ssize_t cpu_rt_runtime_show(struct kobject *kobj,
 168                                    struct kobj_attribute *attr,
 169                                    char *buf)
 170 {
 171         struct user_struct *up = container_of(kobj, struct user_struct, kobj);
 172
 173         return sprintf(buf, "%lu\n", sched_group_rt_runtime(up->tg));
 174 }
 175
 176 static ssize_t cpu_rt_runtime_store(struct kobject *kobj,
 177                                     struct kobj_attribute *attr,
 178                                     const char *buf, size_t size)
 179 {
 180         struct user_struct *up = container_of(kobj, struct user_struct, kobj);
 181         unsigned long rt_runtime;
 182         int rc;
 183
 184         sscanf(buf, "%lu", &rt_runtime);
 185
 186         rc = sched_group_set_rt_runtime(up->tg, rt_runtime);
 187
 188         return (rc ? rc : size);
 189 }
 190
 191 static struct kobj_attribute cpu_rt_runtime_attr =
 192         __ATTR(cpu_rt_runtime, 0644, cpu_rt_runtime_show, cpu_rt_runtime_store);
 193
 194 /* default attributes per uid directory */
 195 static struct attribute *uids_attributes[] = {
 196         &cpu_share_attr.attr,
 197         &cpu_rt_runtime_attr.attr,
 198         NULL
 199 };
 200
 201 /* the lifetime of user_struct is not managed by the core (now) */
 202 static void uids_release(struct kobject *kobj)
 203 {
 204         return;
 205 }
 206
 207 static struct kobj_type uids_ktype = {
 208         .sysfs_ops = &kobj_sysfs_ops,
 209         .default_attrs = uids_attributes,
 210         .release = uids_release,
 211 };
 212
 213 /* create /sys/kernel/uids/<uid>/cpu_share file for this user */
 214 static int uids_user_create(struct user_struct *up)
 215 {
 216         struct kobject *kobj = &up->kobj;
 217         int error;
 218
 219         memset(kobj, 0, sizeof(struct kobject));
 220         kobj->kset = uids_kset;
 221         error = kobject_init_and_add(kobj, &uids_ktype, NULL, "%d", up->uid);
 222         if (error) {
 223                 kobject_put(kobj);
 224                 goto done;
 225         }
 226
 227         kobject_uevent(kobj, KOBJ_ADD);
 228 done:
 229         return error;
 230 }
 231
 232 /* create these entries in sysfs:
 233  *      "/sys/kernel/uids" directory
 234  *      "/sys/kernel/uids/0" directory (for root user)
 235  *      "/sys/kernel/uids/0/cpu_share" file (for root user)
 236  */
 237 int __init uids_sysfs_init(void)
 238 {
 239         uids_kset = kset_create_and_add("uids", NULL, kernel_kobj);
 240         if (!uids_kset)
 241                 return -ENOMEM;
 242
 243         return uids_user_create(&root_user);
 244 }
 245
 246 /* work function to remove sysfs directory for a user and free up
 247  * corresponding structures.
 248  */
 249 static void remove_user_sysfs_dir(struct work_struct *w)
 250 {
 251         struct user_struct *up = container_of(w, struct user_struct, work);
 252         unsigned long flags;
 253         int remove_user = 0;
 254
 255         /* Make uid_hash_remove() + sysfs_remove_file() + kobject_del()
 256          * atomic.
 257          */
 258         uids_mutex_lock();
 259
 260         local_irq_save(flags);
 261
 262         if (atomic_dec_and_lock(&up->__count, &uidhash_lock)) {
 263                 uid_hash_remove(up);
 264                 remove_user = 1;
 265                 spin_unlock_irqrestore(&uidhash_lock, flags);
 266         } else {
 267                 local_irq_restore(flags);
 268         }
 269
 270         if (!remove_user)
 271                 goto done;
 272
 273         kobject_uevent(&up->kobj, KOBJ_REMOVE);
 274         kobject_del(&up->kobj);
 275         kobject_put(&up->kobj);
 276
 277         sched_destroy_user(up);
 278         key_put(up->uid_keyring);
 279         key_put(up->session_keyring);
 280         kmem_cache_free(uid_cachep, up);
 281
 282 done:
 283         uids_mutex_unlock();
 284 }
 285
 286 /* IRQs are disabled and uidhash_lock is held upon function entry.
 287  * IRQ state (as stored in flags) is restored and uidhash_lock released
 288  * upon function exit.
 289  */
 290 static inline void free_user(struct user_struct *up, unsigned long flags)
 291 {
 292         /* restore back the count */
 293         atomic_inc(&up->__count);
 294         spin_unlock_irqrestore(&uidhash_lock, flags);
 295
 296         INIT_WORK(&up->work, remove_user_sysfs_dir);
 297         schedule_work(&up->work);
 298 }
 299
 300 #else   /* CONFIG_FAIR_USER_SCHED && CONFIG_SYSFS */
 301
 302 int uids_sysfs_init(void) { return 0; }
 303 static inline int uids_user_create(struct user_struct *up) { return 0; }
 304 static inline void uids_mutex_lock(void) { }
 305 static inline void uids_mutex_unlock(void) { }
 306
 307 /* IRQs are disabled and uidhash_lock is held upon function entry.
 308  * IRQ state (as stored in flags) is restored and uidhash_lock released
 309  * upon function exit.
 310  */
 311 static inline void free_user(struct user_struct *up, unsigned long flags)
 312 {
 313         uid_hash_remove(up);
 314         spin_unlock_irqrestore(&uidhash_lock, flags);
 315         sched_destroy_user(up);
 316         key_put(up->uid_keyring);
 317         key_put(up->session_keyring);
 318         kmem_cache_free(uid_cachep, up);
 319 }
 320
 321 #endif
 322
 323 /*
 324  * Locate the user_struct for the passed UID.  If found, take a ref on it.  The
 325  * caller must undo that ref with free_uid().
 326  *
 327  * If the user_struct could not be found, return NULL.
 328  */
 329 struct user_struct *find_user(uid_t uid)
 330 {
 331         struct user_struct *ret;
 332         unsigned long flags;
 333         struct user_namespace *ns = current->nsproxy->user_ns;
 334
 335         spin_lock_irqsave(&uidhash_lock, flags);
 336         ret = uid_hash_find(uid, uidhashentry(ns, uid));
 337         spin_unlock_irqrestore(&uidhash_lock, flags);
 338         return ret;
 339 }
 340
 341 void free_uid(struct user_struct *up)
 342 {
 343         unsigned long flags;
 344
 345         if (!up)
 346                 return;
 347
 348         local_irq_save(flags);
 349         if (atomic_dec_and_lock(&up->__count, &uidhash_lock))
 350                 free_user(up, flags);
 351         else
 352                 local_irq_restore(flags);
 353 }
 354
 355 struct user_struct * alloc_uid(struct user_namespace *ns, uid_t uid)
 356 {
 357         struct hlist_head *hashent = uidhashentry(ns, uid);
 358         struct user_struct *up, *new;
 359
 360         /* Make uid_hash_find() + uids_user_create() + uid_hash_insert()
 361          * atomic.
 362          */
 363         uids_mutex_lock();
 364
 365         spin_lock_irq(&uidhash_lock);
 366         up = uid_hash_find(uid, hashent);
 367         spin_unlock_irq(&uidhash_lock);
 368
 369         if (!up) {
 370                 new = kmem_cache_alloc(uid_cachep, GFP_KERNEL);
 371                 if (!new)
 372                         goto out_unlock;
 373
 374                 new->uid = uid;
 375                 atomic_set(&new->__count, 1);
 376                 atomic_set(&new->processes, 0);
 377                 atomic_set(&new->files, 0);
 378                 atomic_set(&new->sigpending, 0);
 379 #ifdef CONFIG_INOTIFY_USER
 380                 atomic_set(&new->inotify_watches, 0);
 381                 atomic_set(&new->inotify_devs, 0);
 382 #endif
 383 #ifdef CONFIG_POSIX_MQUEUE
 384                 new->mq_bytes = 0;
 385 #endif
 386                 new->locked_shm = 0;
 387
 388                 if (alloc_uid_keyring(new, current) < 0)
 389                         goto out_free_user;
 390
 391                 if (sched_create_user(new) < 0)
 392                         goto out_put_keys;
 393
 394                 if (uids_user_create(new))
 395                         goto out_destoy_sched;
 396
 397                 /*
 398                  * Before adding this, check whether we raced
 399                  * on adding the same user already..
 400                  */
 401                 spin_lock_irq(&uidhash_lock);
 402                 up = uid_hash_find(uid, hashent);
 403                 if (up) {
 404                         /* This case is not possible when CONFIG_FAIR_USER_SCHED
 405                          * is defined, since we serialize alloc_uid() using
 406                          * uids_mutex. Hence no need to call
 407                          * sched_destroy_user() or remove_user_sysfs_dir().
 408                          */
 409                         key_put(new->uid_keyring);
 410                         key_put(new->session_keyring);
 411                         kmem_cache_free(uid_cachep, new);
 412                 } else {
 413                         uid_hash_insert(new, hashent);
 414                         up = new;
 415                 }
 416                 spin_unlock_irq(&uidhash_lock);
 417
 418         }
 419
 420         uids_mutex_unlock();
 421
 422         return up;
 423
 424 out_destoy_sched:
 425         sched_destroy_user(new);
 426 out_put_keys:
 427         key_put(new->uid_keyring);
 428         key_put(new->session_keyring);
 429 out_free_user:
 430         kmem_cache_free(uid_cachep, new);
 431 out_unlock:
 432         uids_mutex_unlock();
 433         return NULL;
 434 }
 435
 436 void switch_uid(struct user_struct *new_user)
 437 {
 438         struct user_struct *old_user;
 439
 440         /* What if a process setreuid()'s and this brings the
 441          * new uid over his NPROC rlimit?  We can check this now
 442          * cheaply with the new uid cache, so if it matters
 443          * we should be checking for it.  -DaveM
 444          */
 445         old_user = current->user;
 446         atomic_inc(&new_user->processes);
 447         atomic_dec(&old_user->processes);
 448         switch_uid_keyring(new_user);
 449         current->user = new_user;
 450         sched_switch_user(current);
 451
 452         /*
 453          * We need to synchronize with __sigqueue_alloc()
 454          * doing a get_uid(p->user).. If that saw the old
 455          * user value, we need to wait until it has exited
 456          * its critical region before we can free the old
 457          * structure.
 458          */
 459         smp_mb();
 460         spin_unlock_wait(&current->sighand->siglock);
 461
 462         free_uid(old_user);
 463         suid_keys(current);
 464 }
 465
 466 #ifdef CONFIG_USER_NS
 467 void release_uids(struct user_namespace *ns)
 468 {
 469         int i;
 470         unsigned long flags;
 471         struct hlist_head *head;
 472         struct hlist_node *nd;
 473
 474         spin_lock_irqsave(&uidhash_lock, flags);
 475         /*
 476          * collapse the chains so that the user_struct-s will
 477          * be still alive, but not in hashes. subsequent free_uid()
 478          * will free them.
 479          */
 480         for (i = 0; i < UIDHASH_SZ; i++) {
 481                 head = ns->uidhash_table + i;
 482                 while (!hlist_empty(head)) {
 483                         nd = head->first;
 484                         hlist_del_init(nd);
 485                 }
 486         }
 487         spin_unlock_irqrestore(&uidhash_lock, flags);
 488
 489         free_uid(ns->root_user);
 490 }
 491 #endif
 492
 493 static int __init uid_cache_init(void)
 494 {
 495         int n;
 496
 497         uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
 498                         0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
 499
 500         for(n = 0; n < UIDHASH_SZ; ++n)
 501                 INIT_HLIST_HEAD(init_user_ns.uidhash_table + n);
 502
 503         /* Insert the root user immediately (init already runs as root) */
 504         spin_lock_irq(&uidhash_lock);
 505         uid_hash_insert(&root_user, uidhashentry(&init_user_ns, 0));
 506         spin_unlock_irq(&uidhash_lock);
 507
 508         return 0;
 509 }
 510
 511 module_init(uid_cache_init);