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/*
* 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>
/*
* UID task count cache, to get fast user lookup in "alloc_uid"
* when changing user ID's (ie setuid() and friends).
*/
#define UIDHASH_BITS 8
#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(uid))
static kmem_cache_t *uid_cachep;
static struct user_struct *uidhash_table[UIDHASH_SZ];
static spinlock_t uidhash_lock = SPIN_LOCK_UNLOCKED;
struct user_struct root_user = {
__count: ATOMIC_INIT(1),
processes: ATOMIC_INIT(1),
files: ATOMIC_INIT(0)
};
/*
* These routines must be called with the uidhash spinlock held!
*/
static inline void uid_hash_insert(struct user_struct *up, struct user_struct **hashent)
{
struct user_struct *next = *hashent;
up->next = next;
if (next)
next->pprev = &up->next;
up->pprev = hashent;
*hashent = up;
}
static inline void uid_hash_remove(struct user_struct *up)
{
struct user_struct *next = up->next;
struct user_struct **pprev = up->pprev;
if (next)
next->pprev = pprev;
*pprev = next;
}
static inline struct user_struct *uid_hash_find(uid_t uid, struct user_struct **hashent)
{
struct user_struct *next;
next = *hashent;
for (;;) {
struct user_struct *up = next;
if (next) {
next = up->next;
if (up->uid != uid)
continue;
atomic_inc(&up->__count);
}
return up;
}
}
void free_uid(struct user_struct *up)
{
if (up && atomic_dec_and_lock(&up->__count, &uidhash_lock)) {
uid_hash_remove(up);
kmem_cache_free(uid_cachep, up);
spin_unlock(&uidhash_lock);
}
}
struct user_struct * alloc_uid(uid_t uid)
{
struct user_struct **hashent = uidhashentry(uid);
struct user_struct *up;
spin_lock(&uidhash_lock);
up = uid_hash_find(uid, hashent);
spin_unlock(&uidhash_lock);
if (!up) {
struct user_struct *new;
new = kmem_cache_alloc(uid_cachep, SLAB_KERNEL);
if (!new)
return NULL;
new->uid = uid;
atomic_set(&new->__count, 1);
atomic_set(&new->processes, 0);
atomic_set(&new->files, 0);
/*
* Before adding this, check whether we raced
* on adding the same user already..
*/
spin_lock(&uidhash_lock);
up = uid_hash_find(uid, hashent);
if (up) {
kmem_cache_free(uid_cachep, new);
} else {
uid_hash_insert(new, hashent);
up = new;
}
spin_unlock(&uidhash_lock);
}
return up;
}
void switch_uid(struct user_struct *new_user)
{
struct user_struct *old_user;
/* What if a process setreuid()'s and this brings the
* new uid over his NPROC rlimit? We can check this now
* cheaply with the new uid cache, so if it matters
* we should be checking for it. -DaveM
*/
old_user = current->user;
atomic_inc(&new_user->__count);
atomic_inc(&new_user->processes);
atomic_dec(&old_user->processes);
current->user = new_user;
free_uid(old_user);
}
static int __init uid_cache_init(void)
{
uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
0,
SLAB_HWCACHE_ALIGN, NULL, NULL);
if(!uid_cachep)
panic("Cannot create uid taskcount SLAB cache\n");
/* Insert the root user immediately - init already runs with this */
uid_hash_insert(&root_user, uidhashentry(0));
return 0;
}
module_init(uid_cache_init);
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