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 #include "cred-internals.h"
  20
  21 struct user_namespace init_user_ns = {
  22         .kref = {
  23                 .refcount       = ATOMIC_INIT(2),
  24         },
  25         .creator = &root_user,
  26 };
  27 EXPORT_SYMBOL_GPL(init_user_ns);
  28
  29 /*
  30  * UID task count cache, to get fast user lookup in "alloc_uid"
  31  * when changing user ID's (ie setuid() and friends).
  32  */
  33
  34 #define UIDHASH_MASK            (UIDHASH_SZ - 1)
  35 #define __uidhashfn(uid)        (((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK)
  36 #define uidhashentry(ns, uid)   ((ns)->uidhash_table + __uidhashfn((uid)))
  37
  38 static struct kmem_cache *uid_cachep;
  39
  40 /*
  41  * The uidhash_lock is mostly taken from process context, but it is
  42  * occasionally also taken from softirq/tasklet context, when
  43  * task-structs get RCU-freed. Hence all locking must be softirq-safe.
  44  * But free_uid() is also called with local interrupts disabled, and running
  45  * local_bh_enable() with local interrupts disabled is an error - we'll run
  46  * softirq callbacks, and they can unconditionally enable interrupts, and
  47  * the caller of free_uid() didn't expect that..
  48  */
  49 static DEFINE_SPINLOCK(uidhash_lock);
  50
  51 /* root_user.__count is 2, 1 for init task cred, 1 for init_user_ns->creator */
  52 struct user_struct root_user = {
  53         .__count        = ATOMIC_INIT(2),
  54         .processes      = ATOMIC_INIT(1),
  55         .files          = ATOMIC_INIT(0),
  56         .sigpending     = ATOMIC_INIT(0),
  57         .locked_shm     = 0,
  58         .user_ns        = &init_user_ns,
  59 #ifdef CONFIG_USER_SCHED
  60         .tg             = &init_task_group,
  61 #endif
  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 #ifdef CONFIG_USER_SCHED
  79
  80 static void sched_destroy_user(struct user_struct *up)
  81 {
  82         sched_destroy_group(up->tg);
  83 }
  84
  85 static int sched_create_user(struct user_struct *up)
  86 {
  87         int rc = 0;
  88
  89         up->tg = sched_create_group(&root_task_group);
  90         if (IS_ERR(up->tg))
  91                 rc = -ENOMEM;
  92
  93         set_tg_uid(up);
  94
  95         return rc;
  96 }
  97
  98 #else   /* CONFIG_USER_SCHED */
  99
 100 static void sched_destroy_user(struct user_struct *up) { }
 101 static int sched_create_user(struct user_struct *up) { return 0; }
 102
 103 #endif  /* CONFIG_USER_SCHED */
 104
 105 #if defined(CONFIG_USER_SCHED) && defined(CONFIG_SYSFS)
 106
 107 static struct user_struct *uid_hash_find(uid_t uid, struct hlist_head *hashent)
 108 {
 109         struct user_struct *user;
 110         struct hlist_node *h;
 111
 112         hlist_for_each_entry(user, h, hashent, uidhash_node) {
 113                 if (user->uid == uid) {
 114                         /* possibly resurrect an "almost deleted" object */
 115                         if (atomic_inc_return(&user->__count) == 1)
 116                                 cancel_delayed_work(&user->work);
 117                         return user;
 118                 }
 119         }
 120
 121         return NULL;
 122 }
 123
 124 static struct kset *uids_kset; /* represents the /sys/kernel/uids/ directory */
 125 static DEFINE_MUTEX(uids_mutex);
 126
 127 static inline void uids_mutex_lock(void)
 128 {
 129         mutex_lock(&uids_mutex);
 130 }
 131
 132 static inline void uids_mutex_unlock(void)
 133 {
 134         mutex_unlock(&uids_mutex);
 135 }
 136
 137 /* uid directory attributes */
 138 #ifdef CONFIG_FAIR_GROUP_SCHED
 139 static ssize_t cpu_shares_show(struct kobject *kobj,
 140                                struct kobj_attribute *attr,
 141                                char *buf)
 142 {
 143         struct user_struct *up = container_of(kobj, struct user_struct, kobj);
 144
 145         return sprintf(buf, "%lu\n", sched_group_shares(up->tg));
 146 }
 147
 148 static ssize_t cpu_shares_store(struct kobject *kobj,
 149                                 struct kobj_attribute *attr,
 150                                 const char *buf, size_t size)
 151 {
 152         struct user_struct *up = container_of(kobj, struct user_struct, kobj);
 153         unsigned long shares;
 154         int rc;
 155
 156         sscanf(buf, "%lu", &shares);
 157
 158         rc = sched_group_set_shares(up->tg, shares);
 159
 160         return (rc ? rc : size);
 161 }
 162
 163 static struct kobj_attribute cpu_share_attr =
 164         __ATTR(cpu_share, 0644, cpu_shares_show, cpu_shares_store);
 165 #endif
 166
 167 #ifdef CONFIG_RT_GROUP_SCHED
 168 static ssize_t cpu_rt_runtime_show(struct kobject *kobj,
 169                                    struct kobj_attribute *attr,
 170                                    char *buf)
 171 {
 172         struct user_struct *up = container_of(kobj, struct user_struct, kobj);
 173
 174         return sprintf(buf, "%ld\n", sched_group_rt_runtime(up->tg));
 175 }
 176
 177 static ssize_t cpu_rt_runtime_store(struct kobject *kobj,
 178                                     struct kobj_attribute *attr,
 179                                     const char *buf, size_t size)
 180 {
 181         struct user_struct *up = container_of(kobj, struct user_struct, kobj);
 182         unsigned long rt_runtime;
 183         int rc;
 184
 185         sscanf(buf, "%ld", &rt_runtime);
 186
 187         rc = sched_group_set_rt_runtime(up->tg, rt_runtime);
 188
 189         return (rc ? rc : size);
 190 }
 191
 192 static struct kobj_attribute cpu_rt_runtime_attr =
 193         __ATTR(cpu_rt_runtime, 0644, cpu_rt_runtime_show, cpu_rt_runtime_store);
 194
 195 static ssize_t cpu_rt_period_show(struct kobject *kobj,
 196                                    struct kobj_attribute *attr,
 197                                    char *buf)
 198 {
 199         struct user_struct *up = container_of(kobj, struct user_struct, kobj);
 200
 201         return sprintf(buf, "%lu\n", sched_group_rt_period(up->tg));
 202 }
 203
 204 static ssize_t cpu_rt_period_store(struct kobject *kobj,
 205                                     struct kobj_attribute *attr,
 206                                     const char *buf, size_t size)
 207 {
 208         struct user_struct *up = container_of(kobj, struct user_struct, kobj);
 209         unsigned long rt_period;
 210         int rc;
 211
 212         sscanf(buf, "%lu", &rt_period);
 213
 214         rc = sched_group_set_rt_period(up->tg, rt_period);
 215
 216         return (rc ? rc : size);
 217 }
 218
 219 static struct kobj_attribute cpu_rt_period_attr =
 220         __ATTR(cpu_rt_period, 0644, cpu_rt_period_show, cpu_rt_period_store);
 221 #endif
 222
 223 /* default attributes per uid directory */
 224 static struct attribute *uids_attributes[] = {
 225 #ifdef CONFIG_FAIR_GROUP_SCHED
 226         &cpu_share_attr.attr,
 227 #endif
 228 #ifdef CONFIG_RT_GROUP_SCHED
 229         &cpu_rt_runtime_attr.attr,
 230         &cpu_rt_period_attr.attr,
 231 #endif
 232         NULL
 233 };
 234
 235 /* the lifetime of user_struct is not managed by the core (now) */
 236 static void uids_release(struct kobject *kobj)
 237 {
 238         return;
 239 }
 240
 241 static struct kobj_type uids_ktype = {
 242         .sysfs_ops = &kobj_sysfs_ops,
 243         .default_attrs = uids_attributes,
 244         .release = uids_release,
 245 };
 246
 247 /*
 248  * Create /sys/kernel/uids/<uid>/cpu_share file for this user
 249  * We do not create this file for users in a user namespace (until
 250  * sysfs tagging is implemented).
 251  *
 252  * See Documentation/scheduler/sched-design-CFS.txt for ramifications.
 253  */
 254 static int uids_user_create(struct user_struct *up)
 255 {
 256         struct kobject *kobj = &up->kobj;
 257         int error;
 258
 259         memset(kobj, 0, sizeof(struct kobject));
 260         if (up->user_ns != &init_user_ns)
 261                 return 0;
 262         kobj->kset = uids_kset;
 263         error = kobject_init_and_add(kobj, &uids_ktype, NULL, "%d", up->uid);
 264         if (error) {
 265                 kobject_put(kobj);
 266                 goto done;
 267         }
 268
 269         kobject_uevent(kobj, KOBJ_ADD);
 270 done:
 271         return error;
 272 }
 273
 274 /* create these entries in sysfs:
 275  *      "/sys/kernel/uids" directory
 276  *      "/sys/kernel/uids/0" directory (for root user)
 277  *      "/sys/kernel/uids/0/cpu_share" file (for root user)
 278  */
 279 int __init uids_sysfs_init(void)
 280 {
 281         uids_kset = kset_create_and_add("uids", NULL, kernel_kobj);
 282         if (!uids_kset)
 283                 return -ENOMEM;
 284
 285         return uids_user_create(&root_user);
 286 }
 287
 288 /* delayed work function to remove sysfs directory for a user and free up
 289  * corresponding structures.
 290  */
 291 static void cleanup_user_struct(struct work_struct *w)
 292 {
 293         struct user_struct *up = container_of(w, struct user_struct, work.work);
 294         unsigned long flags;
 295         int remove_user = 0;
 296
 297         /* Make uid_hash_remove() + sysfs_remove_file() + kobject_del()
 298          * atomic.
 299          */
 300         uids_mutex_lock();
 301
 302         spin_lock_irqsave(&uidhash_lock, flags);
 303         if (atomic_read(&up->__count) == 0) {
 304                 uid_hash_remove(up);
 305                 remove_user = 1;
 306         }
 307         spin_unlock_irqrestore(&uidhash_lock, flags);
 308
 309         if (!remove_user)
 310                 goto done;
 311
 312         if (up->user_ns == &init_user_ns) {
 313                 kobject_uevent(&up->kobj, KOBJ_REMOVE);
 314                 kobject_del(&up->kobj);
 315                 kobject_put(&up->kobj);
 316         }
 317
 318         sched_destroy_user(up);
 319         key_put(up->uid_keyring);
 320         key_put(up->session_keyring);
 321         kmem_cache_free(uid_cachep, up);
 322
 323 done:
 324         uids_mutex_unlock();
 325 }
 326
 327 /* IRQs are disabled and uidhash_lock is held upon function entry.
 328  * IRQ state (as stored in flags) is restored and uidhash_lock released
 329  * upon function exit.
 330  */
 331 static void free_user(struct user_struct *up, unsigned long flags)
 332 {
 333         spin_unlock_irqrestore(&uidhash_lock, flags);
 334         INIT_DELAYED_WORK(&up->work, cleanup_user_struct);
 335         schedule_delayed_work(&up->work, msecs_to_jiffies(1000));
 336 }
 337
 338 #else   /* CONFIG_USER_SCHED && CONFIG_SYSFS */
 339
 340 static struct user_struct *uid_hash_find(uid_t uid, struct hlist_head *hashent)
 341 {
 342         struct user_struct *user;
 343         struct hlist_node *h;
 344
 345         hlist_for_each_entry(user, h, hashent, uidhash_node) {
 346                 if (user->uid == uid) {
 347                         atomic_inc(&user->__count);
 348                         return user;
 349                 }
 350         }
 351
 352         return NULL;
 353 }
 354
 355 int uids_sysfs_init(void) { return 0; }
 356 static inline int uids_user_create(struct user_struct *up) { return 0; }
 357 static inline void uids_mutex_lock(void) { }
 358 static inline void uids_mutex_unlock(void) { }
 359
 360 /* IRQs are disabled and uidhash_lock is held upon function entry.
 361  * IRQ state (as stored in flags) is restored and uidhash_lock released
 362  * upon function exit.
 363  */
 364 static void free_user(struct user_struct *up, unsigned long flags)
 365 {
 366         uid_hash_remove(up);
 367         spin_unlock_irqrestore(&uidhash_lock, flags);
 368         sched_destroy_user(up);
 369         key_put(up->uid_keyring);
 370         key_put(up->session_keyring);
 371         kmem_cache_free(uid_cachep, up);
 372 }
 373
 374 #endif
 375
 376 #if defined(CONFIG_RT_GROUP_SCHED) && defined(CONFIG_USER_SCHED)
 377 /*
 378  * We need to check if a setuid can take place. This function should be called
 379  * before successfully completing the setuid.
 380  */
 381 int task_can_switch_user(struct user_struct *up, struct task_struct *tsk)
 382 {
 383
 384         return sched_rt_can_attach(up->tg, tsk);
 385
 386 }
 387 #else
 388 int task_can_switch_user(struct user_struct *up, struct task_struct *tsk)
 389 {
 390         return 1;
 391 }
 392 #endif
 393
 394 /*
 395  * Locate the user_struct for the passed UID.  If found, take a ref on it.  The
 396  * caller must undo that ref with free_uid().
 397  *
 398  * If the user_struct could not be found, return NULL.
 399  */
 400 struct user_struct *find_user(uid_t uid)
 401 {
 402         struct user_struct *ret;
 403         unsigned long flags;
 404         struct user_namespace *ns = current_user_ns();
 405
 406         spin_lock_irqsave(&uidhash_lock, flags);
 407         ret = uid_hash_find(uid, uidhashentry(ns, uid));
 408         spin_unlock_irqrestore(&uidhash_lock, flags);
 409         return ret;
 410 }
 411
 412 void free_uid(struct user_struct *up)
 413 {
 414         unsigned long flags;
 415
 416         if (!up)
 417                 return;
 418
 419         local_irq_save(flags);
 420         if (atomic_dec_and_lock(&up->__count, &uidhash_lock))
 421                 free_user(up, flags);
 422         else
 423                 local_irq_restore(flags);
 424 }
 425
 426 struct user_struct *alloc_uid(struct user_namespace *ns, uid_t uid)
 427 {
 428         struct hlist_head *hashent = uidhashentry(ns, uid);
 429         struct user_struct *up, *new;
 430
 431         /* Make uid_hash_find() + uids_user_create() + uid_hash_insert()
 432          * atomic.
 433          */
 434         uids_mutex_lock();
 435
 436         spin_lock_irq(&uidhash_lock);
 437         up = uid_hash_find(uid, hashent);
 438         spin_unlock_irq(&uidhash_lock);
 439
 440         if (!up) {
 441                 new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL);
 442                 if (!new)
 443                         goto out_unlock;
 444
 445                 new->uid = uid;
 446                 atomic_set(&new->__count, 1);
 447
 448                 if (sched_create_user(new) < 0)
 449                         goto out_free_user;
 450
 451                 new->user_ns = get_user_ns(ns);
 452
 453                 if (uids_user_create(new))
 454                         goto out_destoy_sched;
 455
 456                 /*
 457                  * Before adding this, check whether we raced
 458                  * on adding the same user already..
 459                  */
 460                 spin_lock_irq(&uidhash_lock);
 461                 up = uid_hash_find(uid, hashent);
 462                 if (up) {
 463                         /* This case is not possible when CONFIG_USER_SCHED
 464                          * is defined, since we serialize alloc_uid() using
 465                          * uids_mutex. Hence no need to call
 466                          * sched_destroy_user() or remove_user_sysfs_dir().
 467                          */
 468                         key_put(new->uid_keyring);
 469                         key_put(new->session_keyring);
 470                         kmem_cache_free(uid_cachep, new);
 471                 } else {
 472                         uid_hash_insert(new, hashent);
 473                         up = new;
 474                 }
 475                 spin_unlock_irq(&uidhash_lock);
 476         }
 477
 478         uids_mutex_unlock();
 479
 480         return up;
 481
 482 out_destoy_sched:
 483         sched_destroy_user(new);
 484         put_user_ns(new->user_ns);
 485 out_free_user:
 486         kmem_cache_free(uid_cachep, new);
 487 out_unlock:
 488         uids_mutex_unlock();
 489         return NULL;
 490 }
 491
 492 static int __init uid_cache_init(void)
 493 {
 494         int n;
 495
 496         uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
 497                         0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
 498
 499         for(n = 0; n < UIDHASH_SZ; ++n)
 500                 INIT_HLIST_HEAD(init_user_ns.uidhash_table + n);
 501
 502         /* Insert the root user immediately (init already runs as root) */
 503         spin_lock_irq(&uidhash_lock);
 504         uid_hash_insert(&root_user, uidhashentry(&init_user_ns, 0));
 505         spin_unlock_irq(&uidhash_lock);
 506
 507         return 0;
 508 }
 509
 510 module_init(uid_cache_init);