LXR linux/block/ioprio.c

   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                        /*
  73                         * Originally this only checked for CAP_SYS_ADMIN,
  74                         * which was implicitly allowed for pid 0 by security
  75                         * modules such as SELinux. Make sure we check
  76                         * CAP_SYS_ADMIN first to avoid a denial/avc for
  77                         * possibly missing CAP_SYS_NICE permission.
  78                         */
  79                        if (!capable(CAP_SYS_ADMIN) && !capable(CAP_SYS_NICE))
  80                                return -EPERM;
  81                        fallthrough;
  82                        /* rt has prio field too */
  83                case IOPRIO_CLASS_BE:
  84                        if (data >= IOPRIO_NR_LEVELS || data < 0)
  85                                return -EINVAL;
  86                        break;
  87                case IOPRIO_CLASS_IDLE:
  88                        break;
  89                case IOPRIO_CLASS_NONE:
  90                        if (data)
  91                                return -EINVAL;
  92                        break;
  93                default:
  94                        return -EINVAL;
  95        }
  96
  97        return 0;
  98}
  99
 100SYSCALL_DEFINE3(ioprio_set, int, which, int, who, int, ioprio)
 101{
 102        struct task_struct *p, *g;
 103        struct user_struct *user;
 104        struct pid *pgrp;
 105        kuid_t uid;
 106        int ret;
 107
 108        ret = ioprio_check_cap(ioprio);
 109        if (ret)
 110                return ret;
 111
 112        ret = -ESRCH;
 113        rcu_read_lock();
 114        switch (which) {
 115                case IOPRIO_WHO_PROCESS:
 116                        if (!who)
 117                                p = current;
 118                        else
 119                                p = find_task_by_vpid(who);
 120                        if (p)
 121                                ret = set_task_ioprio(p, ioprio);
 122                        break;
 123                case IOPRIO_WHO_PGRP:
 124                        if (!who)
 125                                pgrp = task_pgrp(current);
 126                        else
 127                                pgrp = find_vpid(who);
 128
 129                        read_lock(&tasklist_lock);
 130                        do_each_pid_thread(pgrp, PIDTYPE_PGID, p) {
 131                                ret = set_task_ioprio(p, ioprio);
 132                                if (ret) {
 133                                        read_unlock(&tasklist_lock);
 134                                        goto out;
 135                                }
 136                        } while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
 137                        read_unlock(&tasklist_lock);
 138
 139                        break;
 140                case IOPRIO_WHO_USER:
 141                        uid = make_kuid(current_user_ns(), who);
 142                        if (!uid_valid(uid))
 143                                break;
 144                        if (!who)
 145                                user = current_user();
 146                        else
 147                                user = find_user(uid);
 148
 149                        if (!user)
 150                                break;
 151
 152                        for_each_process_thread(g, p) {
 153                                if (!uid_eq(task_uid(p), uid) ||
 154                                    !task_pid_vnr(p))
 155                                        continue;
 156                                ret = set_task_ioprio(p, ioprio);
 157                                if (ret)
 158                                        goto free_uid;
 159                        }
 160free_uid:
 161                        if (who)
 162                                free_uid(user);
 163                        break;
 164                default:
 165                        ret = -EINVAL;
 166        }
 167
 168out:
 169        rcu_read_unlock();
 170        return ret;
 171}
 172
 173static int get_task_ioprio(struct task_struct *p)
 174{
 175        int ret;
 176
 177        ret = security_task_getioprio(p);
 178        if (ret)
 179                goto out;
 180        ret = IOPRIO_DEFAULT;
 181        task_lock(p);
 182        if (p->io_context)
 183                ret = p->io_context->ioprio;
 184        task_unlock(p);
 185out:
 186        return ret;
 187}
 188
 189int ioprio_best(unsigned short aprio, unsigned short bprio)
 190{
 191        if (!ioprio_valid(aprio))
 192                aprio = IOPRIO_DEFAULT;
 193        if (!ioprio_valid(bprio))
 194                bprio = IOPRIO_DEFAULT;
 195
 196        return min(aprio, bprio);
 197}
 198
 199SYSCALL_DEFINE2(ioprio_get, int, which, int, who)
 200{
 201        struct task_struct *g, *p;
 202        struct user_struct *user;
 203        struct pid *pgrp;
 204        kuid_t uid;
 205        int ret = -ESRCH;
 206        int tmpio;
 207
 208        rcu_read_lock();
 209        switch (which) {
 210                case IOPRIO_WHO_PROCESS:
 211                        if (!who)
 212                                p = current;
 213                        else
 214                                p = find_task_by_vpid(who);
 215                        if (p)
 216                                ret = get_task_ioprio(p);
 217                        break;
 218                case IOPRIO_WHO_PGRP:
 219                        if (!who)
 220                                pgrp = task_pgrp(current);
 221                        else
 222                                pgrp = find_vpid(who);
 223                        read_lock(&tasklist_lock);
 224                        do_each_pid_thread(pgrp, PIDTYPE_PGID, p) {
 225                                tmpio = get_task_ioprio(p);
 226                                if (tmpio < 0)
 227                                        continue;
 228                                if (ret == -ESRCH)
 229                                        ret = tmpio;
 230                                else
 231                                        ret = ioprio_best(ret, tmpio);
 232                        } while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
 233                        read_unlock(&tasklist_lock);
 234
 235                        break;
 236                case IOPRIO_WHO_USER:
 237                        uid = make_kuid(current_user_ns(), who);
 238                        if (!who)
 239                                user = current_user();
 240                        else
 241                                user = find_user(uid);
 242
 243                        if (!user)
 244                                break;
 245
 246                        for_each_process_thread(g, p) {
 247                                if (!uid_eq(task_uid(p), user->uid) ||
 248                                    !task_pid_vnr(p))
 249                                        continue;
 250                                tmpio = get_task_ioprio(p);
 251                                if (tmpio < 0)
 252                                        continue;
 253                                if (ret == -ESRCH)
 254                                        ret = tmpio;
 255                                else
 256                                        ret = ioprio_best(ret, tmpio);
 257                        }
 258
 259                        if (who)
 260                                free_uid(user);
 261                        break;
 262                default:
 263                        ret = -EINVAL;
 264        }
 265
 266        rcu_read_unlock();
 267        return ret;
 268}
 269