// SPDX-License-Identifier: GPL-2.0
/*
 * fs/ioprio.c
 *
 * Copyright (C) 2004 Jens Axboe <axboe@kernel.dk>
 *
 * Helper functions for setting/querying io priorities of processes. The
 * system calls closely mimmick getpriority/setpriority, see the man page for
 * those. The prio argument is a composite of prio class and prio data, where
 * the data argument has meaning within that class. The standard scheduling
 * classes have 8 distinct prio levels, with 0 being the highest prio and 7
 * being the lowest.
 *
 * IOW, setting BE scheduling class with prio 2 is done ala:
 *
 * unsigned int prio = (IOPRIO_CLASS_BE << IOPRIO_CLASS_SHIFT) | 2;
 *
 * ioprio_set(PRIO_PROCESS, pid, prio);
 *
 * See also Documentation/block/ioprio.rst
 *
 */
#include <linux/gfp.h>
#include <linux/kernel.h>
#include <linux/ioprio.h>
#include <linux/cred.h>
#include <linux/blkdev.h>
#include <linux/capability.h>
#include <linux/syscalls.h>
#include <linux/security.h>
#include <linux/pid_namespace.h>

int ioprio_check_cap(int ioprio)
{
        int class = IOPRIO_PRIO_CLASS(ioprio);
        int level = IOPRIO_PRIO_LEVEL(ioprio);

        switch (class) {
                case IOPRIO_CLASS_RT:
                        /*
                         * Originally this only checked for CAP_SYS_ADMIN,
                         * which was implicitly allowed for pid 0 by security
                         * modules such as SELinux. Make sure we check
                         * CAP_SYS_ADMIN first to avoid a denial/avc for
                         * possibly missing CAP_SYS_NICE permission.
                         */
                        if (!capable(CAP_SYS_ADMIN) && !capable(CAP_SYS_NICE))
                                return -EPERM;
                        break;
                case IOPRIO_CLASS_BE:
                case IOPRIO_CLASS_IDLE:
                        break;
                case IOPRIO_CLASS_NONE:
                        if (level)
                                return -EINVAL;
                        break;
                case IOPRIO_CLASS_INVALID:
                default:
                        return -EINVAL;
        }

        return 0;
}

SYSCALL_DEFINE3(ioprio_set, int, which, int, who, int, ioprio)
{
        struct task_struct *p, *g;
        struct user_struct *user;
        struct pid *pgrp;
        kuid_t uid;
        int ret;

        ret = ioprio_check_cap(ioprio);
        if (ret)
                return ret;

        ret = -ESRCH;
        rcu_read_lock();
        switch (which) {
                case IOPRIO_WHO_PROCESS:
                        if (!who)
                                p = current;
                        else
                                p = find_task_by_vpid(who);
                        if (p)
                                ret = set_task_ioprio(p, ioprio);
                        break;
                case IOPRIO_WHO_PGRP:
                        if (!who)
                                pgrp = task_pgrp(current);
                        else
                                pgrp = find_vpid(who);

                        read_lock(&tasklist_lock);
                        do_each_pid_thread(pgrp, PIDTYPE_PGID, p) {
                                ret = set_task_ioprio(p, ioprio);
                                if (ret) {
                                        read_unlock(&tasklist_lock);
                                        goto out;
                                }
                        } while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
                        read_unlock(&tasklist_lock);

                        break;
                case IOPRIO_WHO_USER:
                        uid = make_kuid(current_user_ns(), who);
                        if (!uid_valid(uid))
                                break;
                        if (!who)
                                user = current_user();
                        else
                                user = find_user(uid);

                        if (!user)
                                break;

                        for_each_process_thread(g, p) {
                                if (!uid_eq(task_uid(p), uid) ||
                                    !task_pid_vnr(p))
                                        continue;
                                ret = set_task_ioprio(p, ioprio);
                                if (ret)
                                        goto free_uid;
                        }
free_uid:
                        if (who)
                                free_uid(user);
                        break;
                default:
                        ret = -EINVAL;
        }

out:
        rcu_read_unlock();
        return ret;
}

static int get_task_ioprio(struct task_struct *p)
{
        int ret;

        ret = security_task_getioprio(p);
        if (ret)
                goto out;
        task_lock(p);
        ret = __get_task_ioprio(p);
        task_unlock(p);
out:
        return ret;
}

/*
 * Return raw IO priority value as set by userspace. We use this for
 * ioprio_get(pid, IOPRIO_WHO_PROCESS) so that we keep historical behavior and
 * also so that userspace can distinguish unset IO priority (which just gets
 * overriden based on task's nice value) from IO priority set to some value.
 */
static int get_task_raw_ioprio(struct task_struct *p)
{
        int ret;

        ret = security_task_getioprio(p);
        if (ret)
                goto out;
        task_lock(p);
        if (p->io_context)
                ret = p->io_context->ioprio;
        else
                ret = IOPRIO_DEFAULT;
        task_unlock(p);
out:
        return ret;
}

static int ioprio_best(unsigned short aprio, unsigned short bprio)
{
        return min(aprio, bprio);
}

SYSCALL_DEFINE2(ioprio_get, int, which, int, who)
{
        struct task_struct *g, *p;
        struct user_struct *user;
        struct pid *pgrp;
        kuid_t uid;
        int ret = -ESRCH;
        int tmpio;

        rcu_read_lock();
        switch (which) {
                case IOPRIO_WHO_PROCESS:
                        if (!who)
                                p = current;
                        else
                                p = find_task_by_vpid(who);
                        if (p)
                                ret = get_task_raw_ioprio(p);
                        break;
                case IOPRIO_WHO_PGRP:
                        if (!who)
                                pgrp = task_pgrp(current);
                        else
                                pgrp = find_vpid(who);
                        read_lock(&tasklist_lock);
                        do_each_pid_thread(pgrp, PIDTYPE_PGID, p) {
                                tmpio = get_task_ioprio(p);
                                if (tmpio < 0)
                                        continue;
                                if (ret == -ESRCH)
                                        ret = tmpio;
                                else
                                        ret = ioprio_best(ret, tmpio);
                        } while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
                        read_unlock(&tasklist_lock);

                        break;
                case IOPRIO_WHO_USER:
                        uid = make_kuid(current_user_ns(), who);
                        if (!who)
                                user = current_user();
                        else
                                user = find_user(uid);

                        if (!user)
                                break;

                        for_each_process_thread(g, p) {
                                if (!uid_eq(task_uid(p), user->uid) ||
                                    !task_pid_vnr(p))
                                        continue;
                                tmpio = get_task_ioprio(p);
                                if (tmpio < 0)
                                        continue;
                                if (ret == -ESRCH)
                                        ret = tmpio;
                                else
                                        ret = ioprio_best(ret, tmpio);
                        }

                        if (who)
                                free_uid(user);
                        break;
                default:
                        ret = -EINVAL;
        }

        rcu_read_unlock();
        return ret;
}