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(1),
  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 }
  76
  77 static struct user_struct *uid_hash_find(uid_t uid, struct hlist_head *hashent)
  78 {
  79         struct user_struct *user;
  80         struct hlist_node *h;
  81
  82         hlist_for_each_entry(user, h, hashent, uidhash_node) {
  83                 if (user->uid == uid) {
  84                         atomic_inc(&user->__count);
  85                         return user;
  86                 }
  87         }
  88
  89         return NULL;
  90 }
  91
  92 #ifdef CONFIG_USER_SCHED
  93
  94 static void sched_destroy_user(struct user_struct *up)
  95 {
  96         sched_destroy_group(up->tg);
  97 }
  98
  99 static int sched_create_user(struct user_struct *up)
 100 {
 101         int rc = 0;
 102
 103         up->tg = sched_create_group(&root_task_group);
 104         if (IS_ERR(up->tg))
 105                 rc = -ENOMEM;
 106
 107         set_tg_uid(up);
 108
 109         return rc;
 110 }
 111
 112 #else   /* CONFIG_USER_SCHED */
 113
 114 static void sched_destroy_user(struct user_struct *up) { }
 115 static int sched_create_user(struct user_struct *up) { return 0; }
 116
 117 #endif  /* CONFIG_USER_SCHED */
 118
 119 #if defined(CONFIG_USER_SCHED) && defined(CONFIG_SYSFS)
 120
 121 static struct kset *uids_kset; /* represents the /sys/kernel/uids/ directory */
 122 static DEFINE_MUTEX(uids_mutex);
 123
 124 static inline void uids_mutex_lock(void)
 125 {
 126         mutex_lock(&uids_mutex);
 127 }
 128
 129 static inline void uids_mutex_unlock(void)
 130 {
 131         mutex_unlock(&uids_mutex);
 132 }
 133
 134 /* uid directory attributes */
 135 #ifdef CONFIG_FAIR_GROUP_SCHED
 136 static ssize_t cpu_shares_show(struct kobject *kobj,
 137                                struct kobj_attribute *attr,
 138                                char *buf)
 139 {
 140         struct user_struct *up = container_of(kobj, struct user_struct, kobj);
 141
 142         return sprintf(buf, "%lu\n", sched_group_shares(up->tg));
 143 }
 144
 145 static ssize_t cpu_shares_store(struct kobject *kobj,
 146                                 struct kobj_attribute *attr,
 147                                 const char *buf, size_t size)
 148 {
 149         struct user_struct *up = container_of(kobj, struct user_struct, kobj);
 150         unsigned long shares;
 151         int rc;
 152
 153         sscanf(buf, "%lu", &shares);
 154
 155         rc = sched_group_set_shares(up->tg, shares);
 156
 157         return (rc ? rc : size);
 158 }
 159
 160 static struct kobj_attribute cpu_share_attr =
 161         __ATTR(cpu_share, 0644, cpu_shares_show, cpu_shares_store);
 162 #endif
 163
 164 #ifdef CONFIG_RT_GROUP_SCHED
 165 static ssize_t cpu_rt_runtime_show(struct kobject *kobj,
 166                                    struct kobj_attribute *attr,
 167                                    char *buf)
 168 {
 169         struct user_struct *up = container_of(kobj, struct user_struct, kobj);
 170
 171         return sprintf(buf, "%ld\n", sched_group_rt_runtime(up->tg));
 172 }
 173
 174 static ssize_t cpu_rt_runtime_store(struct kobject *kobj,
 175                                     struct kobj_attribute *attr,
 176                                     const char *buf, size_t size)
 177 {
 178         struct user_struct *up = container_of(kobj, struct user_struct, kobj);
 179         unsigned long rt_runtime;
 180         int rc;
 181
 182         sscanf(buf, "%ld", &rt_runtime);
 183
 184         rc = sched_group_set_rt_runtime(up->tg, rt_runtime);
 185
 186         return (rc ? rc : size);
 187 }
 188
 189 static struct kobj_attribute cpu_rt_runtime_attr =
 190         __ATTR(cpu_rt_runtime, 0644, cpu_rt_runtime_show, cpu_rt_runtime_store);
 191
 192 static ssize_t cpu_rt_period_show(struct kobject *kobj,
 193                                    struct kobj_attribute *attr,
 194                                    char *buf)
 195 {
 196         struct user_struct *up = container_of(kobj, struct user_struct, kobj);
 197
 198         return sprintf(buf, "%lu\n", sched_group_rt_period(up->tg));
 199 }
 200
 201 static ssize_t cpu_rt_period_store(struct kobject *kobj,
 202                                     struct kobj_attribute *attr,
 203                                     const char *buf, size_t size)
 204 {
 205         struct user_struct *up = container_of(kobj, struct user_struct, kobj);
 206         unsigned long rt_period;
 207         int rc;
 208
 209         sscanf(buf, "%lu", &rt_period);
 210
 211         rc = sched_group_set_rt_period(up->tg, rt_period);
 212
 213         return (rc ? rc : size);
 214 }
 215
 216 static struct kobj_attribute cpu_rt_period_attr =
 217         __ATTR(cpu_rt_period, 0644, cpu_rt_period_show, cpu_rt_period_store);
 218 #endif
 219
 220 /* default attributes per uid directory */
 221 static struct attribute *uids_attributes[] = {
 222 #ifdef CONFIG_FAIR_GROUP_SCHED
 223         &cpu_share_attr.attr,
 224 #endif
 225 #ifdef CONFIG_RT_GROUP_SCHED
 226         &cpu_rt_runtime_attr.attr,
 227         &cpu_rt_period_attr.attr,
 228 #endif
 229         NULL
 230 };
 231
 232 /* the lifetime of user_struct is not managed by the core (now) */
 233 static void uids_release(struct kobject *kobj)
 234 {
 235         return;
 236 }
 237
 238 static struct kobj_type uids_ktype = {
 239         .sysfs_ops = &kobj_sysfs_ops,
 240         .default_attrs = uids_attributes,
 241         .release = uids_release,
 242 };
 243
 244 /*
 245  * Create /sys/kernel/uids/<uid>/cpu_share file for this user
 246  * We do not create this file for users in a user namespace (until
 247  * sysfs tagging is implemented).
 248  *
 249  * See Documentation/scheduler/sched-design-CFS.txt for ramifications.
 250  */
 251 static int uids_user_create(struct user_struct *up)
 252 {
 253         struct kobject *kobj = &up->kobj;
 254         int error;
 255
 256         memset(kobj, 0, sizeof(struct kobject));
 257         if (up->user_ns != &init_user_ns)
 258                 return 0;
 259         kobj->kset = uids_kset;
 260         error = kobject_init_and_add(kobj, &uids_ktype, NULL, "%d", up->uid);
 261         if (error) {
 262                 kobject_put(kobj);
 263                 goto done;
 264         }
 265
 266         kobject_uevent(kobj, KOBJ_ADD);
 267 done:
 268         return error;
 269 }
 270
 271 /* create these entries in sysfs:
 272  *      "/sys/kernel/uids" directory
 273  *      "/sys/kernel/uids/0" directory (for root user)
 274  *      "/sys/kernel/uids/0/cpu_share" file (for root user)
 275  */
 276 int __init uids_sysfs_init(void)
 277 {
 278         uids_kset = kset_create_and_add("uids", NULL, kernel_kobj);
 279         if (!uids_kset)
 280                 return -ENOMEM;
 281
 282         return uids_user_create(&root_user);
 283 }
 284
 285 /* work function to remove sysfs directory for a user and free up
 286  * corresponding structures.
 287  */
 288 static void remove_user_sysfs_dir(struct work_struct *w)
 289 {
 290         struct user_struct *up = container_of(w, struct user_struct, work);
 291         unsigned long flags;
 292         int remove_user = 0;
 293
 294         if (up->user_ns != &init_user_ns)
 295                 return;
 296         /* Make uid_hash_remove() + sysfs_remove_file() + kobject_del()
 297          * atomic.
 298          */
 299         uids_mutex_lock();
 300
 301         local_irq_save(flags);
 302
 303         if (atomic_dec_and_lock(&up->__count, &uidhash_lock)) {
 304                 uid_hash_remove(up);
 305                 remove_user = 1;
 306                 spin_unlock_irqrestore(&uidhash_lock, flags);
 307         } else {
 308                 local_irq_restore(flags);
 309         }
 310
 311         if (!remove_user)
 312                 goto done;
 313
 314         kobject_uevent(&up->kobj, KOBJ_REMOVE);
 315         kobject_del(&up->kobj);
 316         kobject_put(&up->kobj);
 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         /* restore back the count */
 334         atomic_inc(&up->__count);
 335         spin_unlock_irqrestore(&uidhash_lock, flags);
 336
 337         put_user_ns(up->user_ns);
 338         INIT_WORK(&up->work, remove_user_sysfs_dir);
 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         put_user_ns(up->user_ns);
 361         kmem_cache_free(uid_cachep, up);
 362 }
 363
 364 #endif
 365
 366 /*
 367  * Locate the user_struct for the passed UID.  If found, take a ref on it.  The
 368  * caller must undo that ref with free_uid().
 369  *
 370  * If the user_struct could not be found, return NULL.
 371  */
 372 struct user_struct *find_user(uid_t uid)
 373 {
 374         struct user_struct *ret;
 375         unsigned long flags;
 376         struct user_namespace *ns = current_user_ns();
 377
 378         spin_lock_irqsave(&uidhash_lock, flags);
 379         ret = uid_hash_find(uid, uidhashentry(ns, uid));
 380         spin_unlock_irqrestore(&uidhash_lock, flags);
 381         return ret;
 382 }
 383
 384 void free_uid(struct user_struct *up)
 385 {
 386         unsigned long flags;
 387
 388         if (!up)
 389                 return;
 390
 391         local_irq_save(flags);
 392         if (atomic_dec_and_lock(&up->__count, &uidhash_lock))
 393                 free_user(up, flags);
 394         else
 395                 local_irq_restore(flags);
 396 }
 397
 398 struct user_struct *alloc_uid(struct user_namespace *ns, uid_t uid)
 399 {
 400         struct hlist_head *hashent = uidhashentry(ns, uid);
 401         struct user_struct *up, *new;
 402
 403         /* Make uid_hash_find() + uids_user_create() + uid_hash_insert()
 404          * atomic.
 405          */
 406         uids_mutex_lock();
 407
 408         spin_lock_irq(&uidhash_lock);
 409         up = uid_hash_find(uid, hashent);
 410         spin_unlock_irq(&uidhash_lock);
 411
 412         if (!up) {
 413                 new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL);
 414                 if (!new)
 415                         goto out_unlock;
 416
 417                 new->uid = uid;
 418                 atomic_set(&new->__count, 1);
 419
 420                 if (sched_create_user(new) < 0)
 421                         goto out_free_user;
 422
 423                 new->user_ns = get_user_ns(ns);
 424
 425                 if (uids_user_create(new))
 426                         goto out_destoy_sched;
 427
 428                 /*
 429                  * Before adding this, check whether we raced
 430                  * on adding the same user already..
 431                  */
 432                 spin_lock_irq(&uidhash_lock);
 433                 up = uid_hash_find(uid, hashent);
 434                 if (up) {
 435                         /* This case is not possible when CONFIG_USER_SCHED
 436                          * is defined, since we serialize alloc_uid() using
 437                          * uids_mutex. Hence no need to call
 438                          * sched_destroy_user() or remove_user_sysfs_dir().
 439                          */
 440                         key_put(new->uid_keyring);
 441                         key_put(new->session_keyring);
 442                         kmem_cache_free(uid_cachep, new);
 443                 } else {
 444                         uid_hash_insert(new, hashent);
 445                         up = new;
 446                 }
 447                 spin_unlock_irq(&uidhash_lock);
 448         }
 449
 450         uids_mutex_unlock();
 451
 452         return up;
 453
 454 out_destoy_sched:
 455         sched_destroy_user(new);
 456         put_user_ns(new->user_ns);
 457 out_free_user:
 458         kmem_cache_free(uid_cachep, new);
 459 out_unlock:
 460         uids_mutex_unlock();
 461         return NULL;
 462 }
 463
 464 static int __init uid_cache_init(void)
 465 {
 466         int n;
 467
 468         uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
 469                         0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
 470
 471         for(n = 0; n < UIDHASH_SZ; ++n)
 472                 INIT_HLIST_HEAD(init_user_ns.uidhash_table + n);
 473
 474         /* Insert the root user immediately (init already runs as root) */
 475         spin_lock_irq(&uidhash_lock);
 476         uid_hash_insert(&root_user, uidhashentry(&init_user_ns, 0));
 477         spin_unlock_irq(&uidhash_lock);
 478
 479         return 0;
 480 }
 481
 482 module_init(uid_cache_init);