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