/*
 * 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>

/*
 * 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 list_head uidhash_table[UIDHASH_SZ];
static DEFINE_SPINLOCK(uidhash_lock);

struct user_struct root_user = {
        .__count        = ATOMIC_INIT(1),
        .processes      = ATOMIC_INIT(1),
        .files          = ATOMIC_INIT(0),
        .sigpending     = ATOMIC_INIT(0),
        .mq_bytes       = 0,
        .locked_shm     = 0,
#ifdef CONFIG_KEYS
        .uid_keyring    = &root_user_keyring,
        .session_keyring = &root_session_keyring,
#endif
};

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

static inline void uid_hash_remove(struct user_struct *up)
{
        list_del(&up->uidhash_list);
}

static inline struct user_struct *uid_hash_find(uid_t uid, struct list_head *hashent)
{
        struct list_head *up;

        list_for_each(up, hashent) {
                struct user_struct *user;

                user = list_entry(up, struct user_struct, uidhash_list);

                if(user->uid == uid) {
                        atomic_inc(&user->__count);
                        return user;
                }
        }

        return NULL;
}

/*
 * 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(uid_t uid)
{
        struct user_struct *ret;

        spin_lock(&uidhash_lock);
        ret = uid_hash_find(uid, uidhashentry(uid));
        spin_unlock(&uidhash_lock);
        return ret;
}

void free_uid(struct user_struct *up)
{
        if (up && atomic_dec_and_lock(&up->__count, &uidhash_lock)) {
                uid_hash_remove(up);
                key_put(up->uid_keyring);
                key_put(up->session_keyring);
                kmem_cache_free(uid_cachep, up);
                spin_unlock(&uidhash_lock);
        }
}

struct user_struct * alloc_uid(uid_t uid)
{
        struct list_head *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);
                atomic_set(&new->sigpending, 0);

                new->mq_bytes = 0;
                new->locked_shm = 0;

                if (alloc_uid_keyring(new) < 0) {
                        kmem_cache_free(uid_cachep, new);
                        return NULL;
                }

                /*
                 * 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) {
                        key_put(new->uid_keyring);
                        key_put(new->session_keyring);
                        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->processes);
        atomic_dec(&old_user->processes);
        switch_uid_keyring(new_user);
        current->user = new_user;
        free_uid(old_user);
        suid_keys(current);
}


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, NULL);

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

        /* Insert the root user immediately (init already runs as root) */
        spin_lock(&uidhash_lock);
        uid_hash_insert(&root_user, uidhashentry(0));
        spin_unlock(&uidhash_lock);

        return 0;
}

module_init(uid_cache_init);