Quelle user.c Sprache: C

// SPDX-License-Identifier: GPL-2.0-only
/*
* The "user cache".
*
* (C) Copyright 1991-2000 Linus Torvalds
*
* We have a per-user structure to keep track of how many
* processes, files etc the user has claimed, in order to be
* able to have per-user limits for system resources.
*/

#include <linux/init.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/bitops.h>
#include <linux/key.h>
#include <linux/sched/user.h>
#include <linux/interrupt.h>
#include <linux/export.h>
#include <linux/user_namespace.h>
#include <linux/binfmts.h>
#include <linux/proc_ns.h>

#if IS_ENABLED(CONFIG_BINFMT_MISC)
struct binfmt_misc init_binfmt_misc = {
.entries = LIST_HEAD_INIT(init_binfmt_misc.entries),
.enabled = true,
.entries_lock = __RW_LOCK_UNLOCKED(init_binfmt_misc.entries_lock),
};
EXPORT_SYMBOL_GPL(init_binfmt_misc);
#endif

/*
* userns count is 1 for root user, 1 for init_uts_ns,
* and 1 for... ?
*/
struct user_namespace init_user_ns = {
.uid_map = {
  {
   .extent[0] = {
    .first = 0,
    .lower_first = 0,
    .count = 4294967295U,
   },
   .nr_extents = 1,
  },
},
.gid_map = {
  {
   .extent[0] = {
    .first = 0,
    .lower_first = 0,
    .count = 4294967295U,
   },
   .nr_extents = 1,
  },
},
.projid_map = {
  {
   .extent[0] = {
    .first = 0,
    .lower_first = 0,
    .count = 4294967295U,
   },
   .nr_extents = 1,
  },
},
.ns.count = REFCOUNT_INIT(3),
.owner = GLOBAL_ROOT_UID,
.group = GLOBAL_ROOT_GID,
.ns.inum = PROC_USER_INIT_INO,
#ifdef CONFIG_USER_NS
.ns.ops = &userns_operations,
#endif
.flags = USERNS_INIT_FLAGS,
#ifdef CONFIG_KEYS
.keyring_name_list = LIST_HEAD_INIT(init_user_ns.keyring_name_list),
.keyring_sem = __RWSEM_INITIALIZER(init_user_ns.keyring_sem),
#endif
#if IS_ENABLED(CONFIG_BINFMT_MISC)
.binfmt_misc = &init_binfmt_misc,
#endif
};
EXPORT_SYMBOL_GPL(init_user_ns);

/*
* UID task count cache, to get fast user lookup in "alloc_uid"
* when changing user ID's (ie setuid() and friends).
*/

#define UIDHASH_BITS (IS_ENABLED(CONFIG_BASE_SMALL) ? 3 : 7)
#define UIDHASH_SZ (1 << UIDHASH_BITS)
#define UIDHASH_MASK  (UIDHASH_SZ - 1)
#define __uidhashfn(uid) (((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK)
#define uidhashentry(uid) (uidhash_table + __uidhashfn((__kuid_val(uid))))

static struct kmem_cache *uid_cachep;
static struct hlist_head uidhash_table[UIDHASH_SZ];

/*
* The uidhash_lock is mostly taken from process context, but it is
* occasionally also taken from softirq/tasklet context, when
* task-structs get RCU-freed. Hence all locking must be softirq-safe.
* But free_uid() is also called with local interrupts disabled, and running
* local_bh_enable() with local interrupts disabled is an error - we'll run
* softirq callbacks, and they can unconditionally enable interrupts, and
* the caller of free_uid() didn't expect that..
*/
static DEFINE_SPINLOCK(uidhash_lock);

/* root_user.__count is 1, for init task cred */
struct user_struct root_user = {
.__count = REFCOUNT_INIT(1),
.uid  = GLOBAL_ROOT_UID,
.ratelimit = RATELIMIT_STATE_INIT(root_user.ratelimit, 0, 0),
};

/*
* These routines must be called with the uidhash spinlock held!
*/
static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent)
{
hlist_add_head(&up->uidhash_node, hashent);
}

static void uid_hash_remove(struct user_struct *up)
{
hlist_del_init(&up->uidhash_node);
}

static struct user_struct *uid_hash_find(kuid_t uid, struct hlist_head *hashent)
{
struct user_struct *user;

hlist_for_each_entry(user, hashent, uidhash_node) {
  if (uid_eq(user->uid, uid)) {
   refcount_inc(&user->__count);
   return user;
  }
}

return NULL;
}

static int user_epoll_alloc(struct user_struct *up)
{
#ifdef CONFIG_EPOLL
return percpu_counter_init(&up->epoll_watches, 0, GFP_KERNEL);
#else
return 0;
#endif
}

static void user_epoll_free(struct user_struct *up)
{
#ifdef CONFIG_EPOLL
percpu_counter_destroy(&up->epoll_watches);
#endif
}

/* IRQs are disabled and uidhash_lock is held upon function entry.
* IRQ state (as stored in flags) is restored and uidhash_lock released
* upon function exit.
*/
static void free_user(struct user_struct *up, unsigned long flags)
__releases(&uidhash_lock)
{
uid_hash_remove(up);
spin_unlock_irqrestore(&uidhash_lock, flags);
user_epoll_free(up);
kmem_cache_free(uid_cachep, up);
}

/*
* Locate the user_struct for the passed UID.  If found, take a ref on it.  The
* caller must undo that ref with free_uid().
*
* If the user_struct could not be found, return NULL.
*/
struct user_struct *find_user(kuid_t uid)
{
struct user_struct *ret;
unsigned long flags;

spin_lock_irqsave(&uidhash_lock, flags);
ret = uid_hash_find(uid, uidhashentry(uid));
spin_unlock_irqrestore(&uidhash_lock, flags);
return ret;
}

void free_uid(struct user_struct *up)
{
unsigned long flags;

if (!up)
  return;

if (refcount_dec_and_lock_irqsave(&up->__count, &uidhash_lock, &flags))
  free_user(up, flags);
}
EXPORT_SYMBOL_GPL(free_uid);

struct user_struct *alloc_uid(kuid_t uid)
{
struct hlist_head *hashent = uidhashentry(uid);
struct user_struct *up, *new;

spin_lock_irq(&uidhash_lock);
up = uid_hash_find(uid, hashent);
spin_unlock_irq(&uidhash_lock);

if (!up) {
  new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL);
  if (!new)
   return NULL;

  new->uid = uid;
  refcount_set(&new->__count, 1);
  if (user_epoll_alloc(new)) {
   kmem_cache_free(uid_cachep, new);
   return NULL;
  }
  ratelimit_state_init(&new->ratelimit, HZ, 100);
  ratelimit_set_flags(&new->ratelimit, RATELIMIT_MSG_ON_RELEASE);

  /*
* Before adding this, check whether we raced
* on adding the same user already..
*/
  spin_lock_irq(&uidhash_lock);
  up = uid_hash_find(uid, hashent);
  if (up) {
   user_epoll_free(new);
   kmem_cache_free(uid_cachep, new);
  } else {
   uid_hash_insert(new, hashent);
   up = new;
  }
  spin_unlock_irq(&uidhash_lock);
}

return up;
}

static int __init uid_cache_init(void)
{
int n;

uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
   0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);

for(n = 0; n < UIDHASH_SZ; ++n)
  INIT_HLIST_HEAD(uidhash_table + n);

if (user_epoll_alloc(&root_user))
  panic("root_user epoll percpu counter alloc failed");

/* Insert the root user immediately (init already runs as root) */
spin_lock_irq(&uidhash_lock);
uid_hash_insert(&root_user, uidhashentry(GLOBAL_ROOT_UID));
spin_unlock_irq(&uidhash_lock);

return 0;
}
subsys_initcall(uid_cache_init);

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