// SPDX-License-Identifier: GPL-2.0
/*
 * Author: Andrei Vagin <avagin@openvz.org>
 * Author: Dmitry Safonov <dima@arista.com>
 */

#include <linux/time_namespace.h>
#include <linux/user_namespace.h>
#include <linux/sched/signal.h>
#include <linux/sched/task.h>
#include <linux/clocksource.h>
#include <linux/seq_file.h>
#include <linux/proc_ns.h>
#include <linux/export.h>
#include <linux/nstree.h>
#include <linux/time.h>
#include <linux/slab.h>
#include <linux/cred.h>
#include <linux/err.h>
#include <linux/mm.h>

#include <vdso/datapage.h>

ktime_t do_timens_ktime_to_host(clockid_t clockid, ktime_t tim,
                                struct timens_offsets *ns_offsets)
{
        ktime_t offset;

        switch (clockid) {
        case CLOCK_MONOTONIC:
                offset = timespec64_to_ktime(ns_offsets->monotonic);
                break;
        case CLOCK_BOOTTIME:
        case CLOCK_BOOTTIME_ALARM:
                offset = timespec64_to_ktime(ns_offsets->boottime);
                break;
        default:
                return tim;
        }

        /*
         * Check that @tim value is in [offset, KTIME_MAX + offset]
         * and subtract offset.
         */
        if (tim < offset) {
                /*
                 * User can specify @tim *absolute* value - if it's lesser than
                 * the time namespace's offset - it's already expired.
                 */
                tim = 0;
        } else {
                tim = ktime_sub(tim, offset);
                if (unlikely(tim > KTIME_MAX))
                        tim = KTIME_MAX;
        }

        return tim;
}

static struct ucounts *inc_time_namespaces(struct user_namespace *ns)
{
        return inc_ucount(ns, current_euid(), UCOUNT_TIME_NAMESPACES);
}

static void dec_time_namespaces(struct ucounts *ucounts)
{
        dec_ucount(ucounts, UCOUNT_TIME_NAMESPACES);
}

/**
 * clone_time_ns - Clone a time namespace
 * @user_ns:    User namespace which owns a new namespace.
 * @old_ns:     Namespace to clone
 *
 * Clone @old_ns and set the clone refcount to 1
 *
 * Return: The new namespace or ERR_PTR.
 */
static struct time_namespace *clone_time_ns(struct user_namespace *user_ns,
                                          struct time_namespace *old_ns)
{
        struct time_namespace *ns;
        struct ucounts *ucounts;
        int err;

        err = -ENOSPC;
        ucounts = inc_time_namespaces(user_ns);
        if (!ucounts)
                goto fail;

        err = -ENOMEM;
        ns = kzalloc_obj(*ns, GFP_KERNEL_ACCOUNT);
        if (!ns)
                goto fail_dec;

        ns->vvar_page = alloc_page(GFP_KERNEL_ACCOUNT | __GFP_ZERO);
        if (!ns->vvar_page)
                goto fail_free;

        err = ns_common_init(ns);
        if (err)
                goto fail_free_page;

        ns->ucounts = ucounts;
        ns->user_ns = get_user_ns(user_ns);
        ns->offsets = old_ns->offsets;
        ns->frozen_offsets = false;
        ns_tree_add(ns);
        return ns;

fail_free_page:
        __free_page(ns->vvar_page);
fail_free:
        kfree(ns);
fail_dec:
        dec_time_namespaces(ucounts);
fail:
        return ERR_PTR(err);
}

/**
 * copy_time_ns - Create timens_for_children from @old_ns
 * @flags:      Cloning flags
 * @user_ns:    User namespace which owns a new namespace.
 * @old_ns:     Namespace to clone
 *
 * If CLONE_NEWTIME specified in @flags, creates a new timens_for_children;
 * adds a refcounter to @old_ns otherwise.
 *
 * Return: timens_for_children namespace or ERR_PTR.
 */
struct time_namespace *copy_time_ns(u64 flags,
        struct user_namespace *user_ns, struct time_namespace *old_ns)
{
        if (!(flags & CLONE_NEWTIME))
                return get_time_ns(old_ns);

        return clone_time_ns(user_ns, old_ns);
}

static struct timens_offset offset_from_ts(struct timespec64 off)
{
        struct timens_offset ret;

        ret.sec = off.tv_sec;
        ret.nsec = off.tv_nsec;

        return ret;
}

/*
 * A time namespace VVAR page has the same layout as the VVAR page which
 * contains the system wide VDSO data.
 *
 * For a normal task the VVAR pages are installed in the normal ordering:
 *     VVAR
 *     PVCLOCK
 *     HVCLOCK
 *     TIMENS   <- Not really required
 *
 * Now for a timens task the pages are installed in the following order:
 *     TIMENS
 *     PVCLOCK
 *     HVCLOCK
 *     VVAR
 *
 * The check for vdso_clock->clock_mode is in the unlikely path of
 * the seq begin magic. So for the non-timens case most of the time
 * 'seq' is even, so the branch is not taken.
 *
 * If 'seq' is odd, i.e. a concurrent update is in progress, the extra check
 * for vdso_clock->clock_mode is a non-issue. The task is spin waiting for the
 * update to finish and for 'seq' to become even anyway.
 *
 * Timens page has vdso_clock->clock_mode set to VDSO_CLOCKMODE_TIMENS which
 * enforces the time namespace handling path.
 */
static void timens_setup_vdso_clock_data(struct vdso_clock *vc,
                                         struct time_namespace *ns)
{
        struct timens_offset *offset = vc->offset;
        struct timens_offset monotonic = offset_from_ts(ns->offsets.monotonic);
        struct timens_offset boottime = offset_from_ts(ns->offsets.boottime);

        vc->seq                         = 1;
        vc->clock_mode                  = VDSO_CLOCKMODE_TIMENS;
        offset[CLOCK_MONOTONIC]         = monotonic;
        offset[CLOCK_MONOTONIC_RAW]     = monotonic;
        offset[CLOCK_MONOTONIC_COARSE]  = monotonic;
        offset[CLOCK_BOOTTIME]          = boottime;
        offset[CLOCK_BOOTTIME_ALARM]    = boottime;
}

struct page *find_timens_vvar_page(struct vm_area_struct *vma)
{
        if (likely(vma->vm_mm == current->mm))
                return current->nsproxy->time_ns->vvar_page;

        /*
         * VM_PFNMAP | VM_IO protect .fault() handler from being called
         * through interfaces like /proc/$pid/mem or
         * process_vm_{readv,writev}() as long as there's no .access()
         * in special_mapping_vmops().
         * For more details check_vma_flags() and __access_remote_vm()
         */

        WARN(1, "vvar_page accessed remotely");

        return NULL;
}

/*
 * Protects possibly multiple offsets writers racing each other
 * and tasks entering the namespace.
 */
static DEFINE_MUTEX(offset_lock);

static void timens_set_vvar_page(struct task_struct *task,
                                struct time_namespace *ns)
{
        struct vdso_time_data *vdata;
        struct vdso_clock *vc;
        unsigned int i;

        if (ns == &init_time_ns)
                return;

        /* Fast-path, taken by every task in namespace except the first. */
        if (likely(ns->frozen_offsets))
                return;

        mutex_lock(&offset_lock);
        /* Nothing to-do: vvar_page has been already initialized. */
        if (ns->frozen_offsets)
                goto out;

        ns->frozen_offsets = true;
        vdata = page_address(ns->vvar_page);
        vc = vdata->clock_data;

        for (i = 0; i < CS_BASES; i++)
                timens_setup_vdso_clock_data(&vc[i], ns);

        if (IS_ENABLED(CONFIG_POSIX_AUX_CLOCKS)) {
                for (i = 0; i < ARRAY_SIZE(vdata->aux_clock_data); i++)
                        timens_setup_vdso_clock_data(&vdata->aux_clock_data[i], ns);
        }

out:
        mutex_unlock(&offset_lock);
}

void free_time_ns(struct time_namespace *ns)
{
        ns_tree_remove(ns);
        dec_time_namespaces(ns->ucounts);
        put_user_ns(ns->user_ns);
        ns_common_free(ns);
        __free_page(ns->vvar_page);
        /* Concurrent nstree traversal depends on a grace period. */
        kfree_rcu(ns, ns.ns_rcu);
}

static struct ns_common *timens_get(struct task_struct *task)
{
        struct time_namespace *ns = NULL;
        struct nsproxy *nsproxy;

        task_lock(task);
        nsproxy = task->nsproxy;
        if (nsproxy) {
                ns = nsproxy->time_ns;
                get_time_ns(ns);
        }
        task_unlock(task);

        return ns ? &ns->ns : NULL;
}

static struct ns_common *timens_for_children_get(struct task_struct *task)
{
        struct time_namespace *ns = NULL;
        struct nsproxy *nsproxy;

        task_lock(task);
        nsproxy = task->nsproxy;
        if (nsproxy) {
                ns = nsproxy->time_ns_for_children;
                get_time_ns(ns);
        }
        task_unlock(task);

        return ns ? &ns->ns : NULL;
}

static void timens_put(struct ns_common *ns)
{
        put_time_ns(to_time_ns(ns));
}

void timens_commit(struct task_struct *tsk, struct time_namespace *ns)
{
        timens_set_vvar_page(tsk, ns);
        vdso_join_timens(tsk, ns);
}

static int timens_install(struct nsset *nsset, struct ns_common *new)
{
        struct nsproxy *nsproxy = nsset->nsproxy;
        struct time_namespace *ns = to_time_ns(new);

        if (!current_is_single_threaded())
                return -EUSERS;

        if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN) ||
            !ns_capable(nsset->cred->user_ns, CAP_SYS_ADMIN))
                return -EPERM;

        get_time_ns(ns);
        put_time_ns(nsproxy->time_ns);
        nsproxy->time_ns = ns;

        get_time_ns(ns);
        put_time_ns(nsproxy->time_ns_for_children);
        nsproxy->time_ns_for_children = ns;
        return 0;
}

void timens_on_fork(struct nsproxy *nsproxy, struct task_struct *tsk)
{
        struct ns_common *nsc = &nsproxy->time_ns_for_children->ns;
        struct time_namespace *ns = to_time_ns(nsc);

        /* create_new_namespaces() already incremented the ref counter */
        if (nsproxy->time_ns == nsproxy->time_ns_for_children)
                return;

        get_time_ns(ns);
        put_time_ns(nsproxy->time_ns);
        nsproxy->time_ns = ns;

        timens_commit(tsk, ns);
}

static struct user_namespace *timens_owner(struct ns_common *ns)
{
        return to_time_ns(ns)->user_ns;
}

static void show_offset(struct seq_file *m, int clockid, struct timespec64 *ts)
{
        char *clock;

        switch (clockid) {
        case CLOCK_BOOTTIME:
                clock = "boottime";
                break;
        case CLOCK_MONOTONIC:
                clock = "monotonic";
                break;
        default:
                clock = "unknown";
                break;
        }
        seq_printf(m, "%-10s %10lld %9ld\n", clock, ts->tv_sec, ts->tv_nsec);
}

void proc_timens_show_offsets(struct task_struct *p, struct seq_file *m)
{
        struct ns_common *ns;
        struct time_namespace *time_ns;

        ns = timens_for_children_get(p);
        if (!ns)
                return;
        time_ns = to_time_ns(ns);

        show_offset(m, CLOCK_MONOTONIC, &time_ns->offsets.monotonic);
        show_offset(m, CLOCK_BOOTTIME, &time_ns->offsets.boottime);
        put_time_ns(time_ns);
}

int proc_timens_set_offset(struct file *file, struct task_struct *p,
                           struct proc_timens_offset *offsets, int noffsets)
{
        struct ns_common *ns;
        struct time_namespace *time_ns;
        struct timespec64 tp;
        int i, err;

        ns = timens_for_children_get(p);
        if (!ns)
                return -ESRCH;
        time_ns = to_time_ns(ns);

        if (!file_ns_capable(file, time_ns->user_ns, CAP_SYS_TIME)) {
                put_time_ns(time_ns);
                return -EPERM;
        }

        for (i = 0; i < noffsets; i++) {
                struct proc_timens_offset *off = &offsets[i];

                switch (off->clockid) {
                case CLOCK_MONOTONIC:
                        ktime_get_ts64(&tp);
                        break;
                case CLOCK_BOOTTIME:
                        ktime_get_boottime_ts64(&tp);
                        break;
                default:
                        err = -EINVAL;
                        goto out;
                }

                err = -ERANGE;

                if (off->val.tv_sec > KTIME_SEC_MAX ||
                    off->val.tv_sec < -KTIME_SEC_MAX)
                        goto out;

                tp = timespec64_add(tp, off->val);
                /*
                 * KTIME_SEC_MAX is divided by 2 to be sure that KTIME_MAX is
                 * still unreachable.
                 */
                if (tp.tv_sec < 0 || tp.tv_sec > KTIME_SEC_MAX / 2)
                        goto out;
        }

        mutex_lock(&offset_lock);
        if (time_ns->frozen_offsets) {
                err = -EACCES;
                goto out_unlock;
        }

        err = 0;
        /* Don't report errors after this line */
        for (i = 0; i < noffsets; i++) {
                struct proc_timens_offset *off = &offsets[i];
                struct timespec64 *offset = NULL;

                switch (off->clockid) {
                case CLOCK_MONOTONIC:
                        offset = &time_ns->offsets.monotonic;
                        break;
                case CLOCK_BOOTTIME:
                        offset = &time_ns->offsets.boottime;
                        break;
                }

                *offset = off->val;
        }

out_unlock:
        mutex_unlock(&offset_lock);
out:
        put_time_ns(time_ns);

        return err;
}

const struct proc_ns_operations timens_operations = {
        .name           = "time",
        .get            = timens_get,
        .put            = timens_put,
        .install        = timens_install,
        .owner          = timens_owner,
};

const struct proc_ns_operations timens_for_children_operations = {
        .name           = "time_for_children",
        .real_ns_name   = "time",
        .get            = timens_for_children_get,
        .put            = timens_put,
        .install        = timens_install,
        .owner          = timens_owner,
};

struct time_namespace init_time_ns = {
        .ns             = NS_COMMON_INIT(init_time_ns),
        .user_ns        = &init_user_ns,
        .frozen_offsets = true,
};

void __init time_ns_init(void)
{
        ns_tree_add(&init_time_ns);
}