/*
 * 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/interrupt.h>
#include <linux/module.h>
#include <linux/user_namespace.h>

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

#define UIDHASH_MASK            (UIDHASH_SZ - 1)
#define __uidhashfn(uid)        (((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK)
#define uidhashentry(ns, uid)   ((ns)->uidhash_table + __uidhashfn((uid)))

static struct kmem_cache *uid_cachep;

/*
 * 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);

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

/*
 * 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(uid_t uid, struct hlist_head *hashent)
{
        struct user_struct *user;
        struct hlist_node *h;

        hlist_for_each_entry(user, h, hashent, uidhash_node) {
                if (user->uid == uid) {
                        atomic_inc(&user->__count);
                        return user;
                }
        }

        return NULL;
}

#ifdef CONFIG_FAIR_USER_SCHED

static void sched_destroy_user(struct user_struct *up)
{
        sched_destroy_group(up->tg);
}

static int sched_create_user(struct user_struct *up)
{
        int rc = 0;

        up->tg = sched_create_group();
        if (IS_ERR(up->tg))
                rc = -ENOMEM;

        return rc;
}

static void sched_switch_user(struct task_struct *p)
{
        sched_move_task(p);
}

#else   /* CONFIG_FAIR_USER_SCHED */

static void sched_destroy_user(struct user_struct *up) { }
static int sched_create_user(struct user_struct *up) { return 0; }
static void sched_switch_user(struct task_struct *p) { }

#endif  /* CONFIG_FAIR_USER_SCHED */

#if defined(CONFIG_FAIR_USER_SCHED) && defined(CONFIG_SYSFS)

static struct kobject uids_kobject; /* represents /sys/kernel/uids directory */
static DEFINE_MUTEX(uids_mutex);

static inline void uids_mutex_lock(void)
{
        mutex_lock(&uids_mutex);
}

static inline void uids_mutex_unlock(void)
{
        mutex_unlock(&uids_mutex);
}

/* return cpu shares held by the user */
static ssize_t cpu_shares_show(struct kset *kset, char *buffer)
{
        struct user_struct *up = container_of(kset, struct user_struct, kset);

        return sprintf(buffer, "%lu\n", sched_group_shares(up->tg));
}

/* modify cpu shares held by the user */
static ssize_t cpu_shares_store(struct kset *kset, const char *buffer,
                                size_t size)
{
        struct user_struct *up = container_of(kset, struct user_struct, kset);
        unsigned long shares;
        int rc;

        sscanf(buffer, "%lu", &shares);

        rc = sched_group_set_shares(up->tg, shares);

        return (rc ? rc : size);
}

static void user_attr_init(struct subsys_attribute *sa, char *name, int mode)
{
        sa->attr.name = name;
        sa->attr.mode = mode;
        sa->show = cpu_shares_show;
        sa->store = cpu_shares_store;
}

/* Create "/sys/kernel/uids/<uid>" directory and
 *  "/sys/kernel/uids/<uid>/cpu_share" file for this user.
 */
static int user_kobject_create(struct user_struct *up)
{
        struct kset *kset = &up->kset;
        struct kobject *kobj = &kset->kobj;
        int error;

        memset(kset, 0, sizeof(struct kset));
        kobj->parent = &uids_kobject;   /* create under /sys/kernel/uids dir */
        kobject_set_name(kobj, "%d", up->uid);
        kset_init(kset);
        user_attr_init(&up->user_attr, "cpu_share", 0644);

        error = kobject_add(kobj);
        if (error)
                goto done;

        error = sysfs_create_file(kobj, &up->user_attr.attr);
        if (error)
                kobject_del(kobj);

        kobject_uevent(kobj, KOBJ_ADD);

done:
        return error;
}

/* create these in sysfs filesystem:
 *      "/sys/kernel/uids" directory
 *      "/sys/kernel/uids/0" directory (for root user)
 *      "/sys/kernel/uids/0/cpu_share" file (for root user)
 */
int __init uids_kobject_init(void)
{
        int error;

        /* create under /sys/kernel dir */
        uids_kobject.parent = &kernel_subsys.kobj;
        uids_kobject.kset = &kernel_subsys;
        kobject_set_name(&uids_kobject, "uids");
        kobject_init(&uids_kobject);

        error = kobject_add(&uids_kobject);
        if (!error)
                error = user_kobject_create(&root_user);

        return error;
}

/* work function to remove sysfs directory for a user and free up
 * corresponding structures.
 */
static void remove_user_sysfs_dir(struct work_struct *w)
{
        struct user_struct *up = container_of(w, struct user_struct, work);
        struct kobject *kobj = &up->kset.kobj;
        unsigned long flags;
        int remove_user = 0;

        /* Make uid_hash_remove() + sysfs_remove_file() + kobject_del()
         * atomic.
         */
        uids_mutex_lock();

        local_irq_save(flags);

        if (atomic_dec_and_lock(&up->__count, &uidhash_lock)) {
                uid_hash_remove(up);
                remove_user = 1;
                spin_unlock_irqrestore(&uidhash_lock, flags);
        } else {
                local_irq_restore(flags);
        }

        if (!remove_user)
                goto done;

        sysfs_remove_file(kobj, &up->user_attr.attr);
        kobject_uevent(kobj, KOBJ_REMOVE);
        kobject_del(kobj);

        sched_destroy_user(up);
        key_put(up->uid_keyring);
        key_put(up->session_keyring);
        kmem_cache_free(uid_cachep, up);

done:
        uids_mutex_unlock();
}

/* 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 inline void free_user(struct user_struct *up, unsigned long flags)
{
        /* restore back the count */
        atomic_inc(&up->__count);
        spin_unlock_irqrestore(&uidhash_lock, flags);

        INIT_WORK(&up->work, remove_user_sysfs_dir);
        schedule_work(&up->work);
}

#else   /* CONFIG_FAIR_USER_SCHED && CONFIG_SYSFS */

static inline int user_kobject_create(struct user_struct *up) { return 0; }
static inline void uids_mutex_lock(void) { }
static inline void uids_mutex_unlock(void) { }

/* 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 inline void free_user(struct user_struct *up, unsigned long flags)
{
        uid_hash_remove(up);
        spin_unlock_irqrestore(&uidhash_lock, flags);
        sched_destroy_user(up);
        key_put(up->uid_keyring);
        key_put(up->session_keyring);
        kmem_cache_free(uid_cachep, up);
}

#endif

/*
 * 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;
        unsigned long flags;
        struct user_namespace *ns = current->nsproxy->user_ns;

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

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

        if (!up)
                return;

        local_irq_save(flags);
        if (atomic_dec_and_lock(&up->__count, &uidhash_lock))
                free_user(up, flags);
        else
                local_irq_restore(flags);
}

struct user_struct * alloc_uid(struct user_namespace *ns, uid_t uid)
{
        struct hlist_head *hashent = uidhashentry(ns, uid);
        struct user_struct *up;

        /* Make uid_hash_find() + user_kobject_create() + uid_hash_insert()
         * atomic.
         */
        uids_mutex_lock();

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

        if (!up) {
                struct user_struct *new;

                new = kmem_cache_alloc(uid_cachep, GFP_KERNEL);
                if (!new) {
                        uids_mutex_unlock();
                        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);
#ifdef CONFIG_INOTIFY_USER
                atomic_set(&new->inotify_watches, 0);
                atomic_set(&new->inotify_devs, 0);
#endif
#ifdef CONFIG_POSIX_MQUEUE
                new->mq_bytes = 0;
#endif
                new->locked_shm = 0;

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

                if (sched_create_user(new) < 0) {
                        key_put(new->uid_keyring);
                        key_put(new->session_keyring);
                        kmem_cache_free(uid_cachep, new);
                        uids_mutex_unlock();
                        return NULL;
                }

                if (user_kobject_create(new)) {
                        sched_destroy_user(new);
                        key_put(new->uid_keyring);
                        key_put(new->session_keyring);
                        kmem_cache_free(uid_cachep, new);
                        uids_mutex_unlock();
                        return NULL;
                }

                /*
                 * 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) {
                        /* This case is not possible when CONFIG_FAIR_USER_SCHED
                         * is defined, since we serialize alloc_uid() using
                         * uids_mutex. Hence no need to call
                         * sched_destroy_user() or remove_user_sysfs_dir().
                         */
                        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_irq(&uidhash_lock);

        }

        uids_mutex_unlock();

        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;
        sched_switch_user(current);

        /*
         * We need to synchronize with __sigqueue_alloc()
         * doing a get_uid(p->user).. If that saw the old
         * user value, we need to wait until it has exited
         * its critical region before we can free the old
         * structure.
         */
        smp_mb();
        spin_unlock_wait(&current->sighand->siglock);

        free_uid(old_user);
        suid_keys(current);
}

void release_uids(struct user_namespace *ns)
{
        int i;
        unsigned long flags;
        struct hlist_head *head;
        struct hlist_node *nd;

        spin_lock_irqsave(&uidhash_lock, flags);
        /*
         * collapse the chains so that the user_struct-s will
         * be still alive, but not in hashes. subsequent free_uid()
         * will free them.
         */
        for (i = 0; i < UIDHASH_SZ; i++) {
                head = ns->uidhash_table + i;
                while (!hlist_empty(head)) {
                        nd = head->first;
                        hlist_del_init(nd);
                }
        }
        spin_unlock_irqrestore(&uidhash_lock, flags);

        free_uid(ns->root_user);
}

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(init_user_ns.uidhash_table + n);

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

        return 0;
}

module_init(uid_cache_init);