linux/block/ioprio.c
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   1// SPDX-License-Identifier: GPL-2.0
   2/*
   3 * fs/ioprio.c
   4 *
   5 * Copyright (C) 2004 Jens Axboe <axboe@kernel.dk>
   6 *
   7 * Helper functions for setting/querying io priorities of processes. The
   8 * system calls closely mimmick getpriority/setpriority, see the man page for
   9 * those. The prio argument is a composite of prio class and prio data, where
  10 * the data argument has meaning within that class. The standard scheduling
  11 * classes have 8 distinct prio levels, with 0 being the highest prio and 7
  12 * being the lowest.
  13 *
  14 * IOW, setting BE scheduling class with prio 2 is done ala:
  15 *
  16 * unsigned int prio = (IOPRIO_CLASS_BE << IOPRIO_CLASS_SHIFT) | 2;
  17 *
  18 * ioprio_set(PRIO_PROCESS, pid, prio);
  19 *
  20 * See also Documentation/block/ioprio.rst
  21 *
  22 */
  23#include <linux/gfp.h>
  24#include <linux/kernel.h>
  25#include <linux/export.h>
  26#include <linux/ioprio.h>
  27#include <linux/cred.h>
  28#include <linux/blkdev.h>
  29#include <linux/capability.h>
  30#include <linux/sched/user.h>
  31#include <linux/sched/task.h>
  32#include <linux/syscalls.h>
  33#include <linux/security.h>
  34#include <linux/pid_namespace.h>
  35
  36int set_task_ioprio(struct task_struct *task, int ioprio)
  37{
  38        int err;
  39        struct io_context *ioc;
  40        const struct cred *cred = current_cred(), *tcred;
  41
  42        rcu_read_lock();
  43        tcred = __task_cred(task);
  44        if (!uid_eq(tcred->uid, cred->euid) &&
  45            !uid_eq(tcred->uid, cred->uid) && !capable(CAP_SYS_NICE)) {
  46                rcu_read_unlock();
  47                return -EPERM;
  48        }
  49        rcu_read_unlock();
  50
  51        err = security_task_setioprio(task, ioprio);
  52        if (err)
  53                return err;
  54
  55        ioc = get_task_io_context(task, GFP_ATOMIC, NUMA_NO_NODE);
  56        if (ioc) {
  57                ioc->ioprio = ioprio;
  58                put_io_context(ioc);
  59        }
  60
  61        return err;
  62}
  63EXPORT_SYMBOL_GPL(set_task_ioprio);
  64
  65int ioprio_check_cap(int ioprio)
  66{
  67        int class = IOPRIO_PRIO_CLASS(ioprio);
  68        int data = IOPRIO_PRIO_DATA(ioprio);
  69
  70        switch (class) {
  71                case IOPRIO_CLASS_RT:
  72                        if (!capable(CAP_SYS_NICE) && !capable(CAP_SYS_ADMIN))
  73                                return -EPERM;
  74                        fallthrough;
  75                        /* rt has prio field too */
  76                case IOPRIO_CLASS_BE:
  77                        if (data >= IOPRIO_NR_LEVELS || data < 0)
  78                                return -EINVAL;
  79                        break;
  80                case IOPRIO_CLASS_IDLE:
  81                        break;
  82                case IOPRIO_CLASS_NONE:
  83                        if (data)
  84                                return -EINVAL;
  85                        break;
  86                default:
  87                        return -EINVAL;
  88        }
  89
  90        return 0;
  91}
  92
  93SYSCALL_DEFINE3(ioprio_set, int, which, int, who, int, ioprio)
  94{
  95        struct task_struct *p, *g;
  96        struct user_struct *user;
  97        struct pid *pgrp;
  98        kuid_t uid;
  99        int ret;
 100
 101        ret = ioprio_check_cap(ioprio);
 102        if (ret)
 103                return ret;
 104
 105        ret = -ESRCH;
 106        rcu_read_lock();
 107        switch (which) {
 108                case IOPRIO_WHO_PROCESS:
 109                        if (!who)
 110                                p = current;
 111                        else
 112                                p = find_task_by_vpid(who);
 113                        if (p)
 114                                ret = set_task_ioprio(p, ioprio);
 115                        break;
 116                case IOPRIO_WHO_PGRP:
 117                        if (!who)
 118                                pgrp = task_pgrp(current);
 119                        else
 120                                pgrp = find_vpid(who);
 121
 122                        read_lock(&tasklist_lock);
 123                        do_each_pid_thread(pgrp, PIDTYPE_PGID, p) {
 124                                ret = set_task_ioprio(p, ioprio);
 125                                if (ret) {
 126                                        read_unlock(&tasklist_lock);
 127                                        goto out;
 128                                }
 129                        } while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
 130                        read_unlock(&tasklist_lock);
 131
 132                        break;
 133                case IOPRIO_WHO_USER:
 134                        uid = make_kuid(current_user_ns(), who);
 135                        if (!uid_valid(uid))
 136                                break;
 137                        if (!who)
 138                                user = current_user();
 139                        else
 140                                user = find_user(uid);
 141
 142                        if (!user)
 143                                break;
 144
 145                        for_each_process_thread(g, p) {
 146                                if (!uid_eq(task_uid(p), uid) ||
 147                                    !task_pid_vnr(p))
 148                                        continue;
 149                                ret = set_task_ioprio(p, ioprio);
 150                                if (ret)
 151                                        goto free_uid;
 152                        }
 153free_uid:
 154                        if (who)
 155                                free_uid(user);
 156                        break;
 157                default:
 158                        ret = -EINVAL;
 159        }
 160
 161out:
 162        rcu_read_unlock();
 163        return ret;
 164}
 165
 166static int get_task_ioprio(struct task_struct *p)
 167{
 168        int ret;
 169
 170        ret = security_task_getioprio(p);
 171        if (ret)
 172                goto out;
 173        ret = IOPRIO_DEFAULT;
 174        task_lock(p);
 175        if (p->io_context)
 176                ret = p->io_context->ioprio;
 177        task_unlock(p);
 178out:
 179        return ret;
 180}
 181
 182int ioprio_best(unsigned short aprio, unsigned short bprio)
 183{
 184        if (!ioprio_valid(aprio))
 185                aprio = IOPRIO_DEFAULT;
 186        if (!ioprio_valid(bprio))
 187                bprio = IOPRIO_DEFAULT;
 188
 189        return min(aprio, bprio);
 190}
 191
 192SYSCALL_DEFINE2(ioprio_get, int, which, int, who)
 193{
 194        struct task_struct *g, *p;
 195        struct user_struct *user;
 196        struct pid *pgrp;
 197        kuid_t uid;
 198        int ret = -ESRCH;
 199        int tmpio;
 200
 201        rcu_read_lock();
 202        switch (which) {
 203                case IOPRIO_WHO_PROCESS:
 204                        if (!who)
 205                                p = current;
 206                        else
 207                                p = find_task_by_vpid(who);
 208                        if (p)
 209                                ret = get_task_ioprio(p);
 210                        break;
 211                case IOPRIO_WHO_PGRP:
 212                        if (!who)
 213                                pgrp = task_pgrp(current);
 214                        else
 215                                pgrp = find_vpid(who);
 216                        do_each_pid_thread(pgrp, PIDTYPE_PGID, p) {
 217                                tmpio = get_task_ioprio(p);
 218                                if (tmpio < 0)
 219                                        continue;
 220                                if (ret == -ESRCH)
 221                                        ret = tmpio;
 222                                else
 223                                        ret = ioprio_best(ret, tmpio);
 224                        } while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
 225                        break;
 226                case IOPRIO_WHO_USER:
 227                        uid = make_kuid(current_user_ns(), who);
 228                        if (!who)
 229                                user = current_user();
 230                        else
 231                                user = find_user(uid);
 232
 233                        if (!user)
 234                                break;
 235
 236                        for_each_process_thread(g, p) {
 237                                if (!uid_eq(task_uid(p), user->uid) ||
 238                                    !task_pid_vnr(p))
 239                                        continue;
 240                                tmpio = get_task_ioprio(p);
 241                                if (tmpio < 0)
 242                                        continue;
 243                                if (ret == -ESRCH)
 244                                        ret = tmpio;
 245                                else
 246                                        ret = ioprio_best(ret, tmpio);
 247                        }
 248
 249                        if (who)
 250                                free_uid(user);
 251                        break;
 252                default:
 253                        ret = -EINVAL;
 254        }
 255
 256        rcu_read_unlock();
 257        return ret;
 258}
 259