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/ioprio.h>
  26 #include <linux/cred.h>
  27 #include <linux/blkdev.h>
  28 #include <linux/capability.h>
  29 #include <linux/syscalls.h>
  30 #include <linux/security.h>
  31 #include <linux/pid_namespace.h>
  32
  33 int ioprio_check_cap(int ioprio)
  34 {
  35         int class = IOPRIO_PRIO_CLASS(ioprio);
  36         int level = IOPRIO_PRIO_LEVEL(ioprio);
  37
  38         switch (class) {
  39                 case IOPRIO_CLASS_RT:
  40                         /*
  41                          * Originally this only checked for CAP_SYS_ADMIN,
  42                          * which was implicitly allowed for pid 0 by security
  43                          * modules such as SELinux. Make sure we check
  44                          * CAP_SYS_ADMIN first to avoid a denial/avc for
  45                          * possibly missing CAP_SYS_NICE permission.
  46                          */
  47                         if (!capable(CAP_SYS_ADMIN) && !capable(CAP_SYS_NICE))
  48                                 return -EPERM;
  49                         fallthrough;
  50                         /* rt has prio field too */
  51                 case IOPRIO_CLASS_BE:
  52                         if (level >= IOPRIO_NR_LEVELS)
  53                                 return -EINVAL;
  54                         break;
  55                 case IOPRIO_CLASS_IDLE:
  56                         break;
  57                 case IOPRIO_CLASS_NONE:
  58                         if (level)
  59                                 return -EINVAL;
  60                         break;
  61                 case IOPRIO_CLASS_INVALID:
  62                 default:
  63                         return -EINVAL;
  64         }
  65
  66         return 0;
  67 }
  68
  69 SYSCALL_DEFINE3(ioprio_set, int, which, int, who, int, ioprio)
  70 {
  71         struct task_struct *p, *g;
  72         struct user_struct *user;
  73         struct pid *pgrp;
  74         kuid_t uid;
  75         int ret;
  76
  77         ret = ioprio_check_cap(ioprio);
  78         if (ret)
  79                 return ret;
  80
  81         ret = -ESRCH;
  82         rcu_read_lock();
  83         switch (which) {
  84                 case IOPRIO_WHO_PROCESS:
  85                         if (!who)
  86                                 p = current;
  87                         else
  88                                 p = find_task_by_vpid(who);
  89                         if (p)
  90                                 ret = set_task_ioprio(p, ioprio);
  91                         break;
  92                 case IOPRIO_WHO_PGRP:
  93                         if (!who)
  94                                 pgrp = task_pgrp(current);
  95                         else
  96                                 pgrp = find_vpid(who);
  97
  98                         read_lock(&tasklist_lock);
  99                         do_each_pid_thread(pgrp, PIDTYPE_PGID, p) {
 100                                 ret = set_task_ioprio(p, ioprio);
 101                                 if (ret) {
 102                                         read_unlock(&tasklist_lock);
 103                                         goto out;
 104                                 }
 105                         } while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
 106                         read_unlock(&tasklist_lock);
 107
 108                         break;
 109                 case IOPRIO_WHO_USER:
 110                         uid = make_kuid(current_user_ns(), who);
 111                         if (!uid_valid(uid))
 112                                 break;
 113                         if (!who)
 114                                 user = current_user();
 115                         else
 116                                 user = find_user(uid);
 117
 118                         if (!user)
 119                                 break;
 120
 121                         for_each_process_thread(g, p) {
 122                                 if (!uid_eq(task_uid(p), uid) ||
 123                                     !task_pid_vnr(p))
 124                                         continue;
 125                                 ret = set_task_ioprio(p, ioprio);
 126                                 if (ret)
 127                                         goto free_uid;
 128                         }
 129 free_uid:
 130                         if (who)
 131                                 free_uid(user);
 132                         break;
 133                 default:
 134                         ret = -EINVAL;
 135         }
 136
 137 out:
 138         rcu_read_unlock();
 139         return ret;
 140 }
 141
 142 /*
 143  * If the task has set an I/O priority, use that. Otherwise, return
 144  * the default I/O priority.
 145  *
 146  * Expected to be called for current task or with task_lock() held to keep
 147  * io_context stable.
 148  */
 149 int __get_task_ioprio(struct task_struct *p)
 150 {
 151         struct io_context *ioc = p->io_context;
 152         int prio;
 153
 154         if (p != current)
 155                 lockdep_assert_held(&p->alloc_lock);
 156         if (ioc)
 157                 prio = ioc->ioprio;
 158         else
 159                 prio = IOPRIO_DEFAULT;
 160
 161         if (IOPRIO_PRIO_CLASS(prio) == IOPRIO_CLASS_NONE)
 162                 prio = IOPRIO_PRIO_VALUE(task_nice_ioclass(p),
 163                                          task_nice_ioprio(p));
 164         return prio;
 165 }
 166 EXPORT_SYMBOL_GPL(__get_task_ioprio);
 167
 168 static int get_task_ioprio(struct task_struct *p)
 169 {
 170         int ret;
 171
 172         ret = security_task_getioprio(p);
 173         if (ret)
 174                 goto out;
 175         task_lock(p);
 176         ret = __get_task_ioprio(p);
 177         task_unlock(p);
 178 out:
 179         return ret;
 180 }
 181
 182 /*
 183  * Return raw IO priority value as set by userspace. We use this for
 184  * ioprio_get(pid, IOPRIO_WHO_PROCESS) so that we keep historical behavior and
 185  * also so that userspace can distinguish unset IO priority (which just gets
 186  * overriden based on task's nice value) from IO priority set to some value.
 187  */
 188 static int get_task_raw_ioprio(struct task_struct *p)
 189 {
 190         int ret;
 191
 192         ret = security_task_getioprio(p);
 193         if (ret)
 194                 goto out;
 195         task_lock(p);
 196         if (p->io_context)
 197                 ret = p->io_context->ioprio;
 198         else
 199                 ret = IOPRIO_DEFAULT;
 200         task_unlock(p);
 201 out:
 202         return ret;
 203 }
 204
 205 static int ioprio_best(unsigned short aprio, unsigned short bprio)
 206 {
 207         return min(aprio, bprio);
 208 }
 209
 210 SYSCALL_DEFINE2(ioprio_get, int, which, int, who)
 211 {
 212         struct task_struct *g, *p;
 213         struct user_struct *user;
 214         struct pid *pgrp;
 215         kuid_t uid;
 216         int ret = -ESRCH;
 217         int tmpio;
 218
 219         rcu_read_lock();
 220         switch (which) {
 221                 case IOPRIO_WHO_PROCESS:
 222                         if (!who)
 223                                 p = current;
 224                         else
 225                                 p = find_task_by_vpid(who);
 226                         if (p)
 227                                 ret = get_task_raw_ioprio(p);
 228                         break;
 229                 case IOPRIO_WHO_PGRP:
 230                         if (!who)
 231                                 pgrp = task_pgrp(current);
 232                         else
 233                                 pgrp = find_vpid(who);
 234                         read_lock(&tasklist_lock);
 235                         do_each_pid_thread(pgrp, PIDTYPE_PGID, p) {
 236                                 tmpio = get_task_ioprio(p);
 237                                 if (tmpio < 0)
 238                                         continue;
 239                                 if (ret == -ESRCH)
 240                                         ret = tmpio;
 241                                 else
 242                                         ret = ioprio_best(ret, tmpio);
 243                         } while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
 244                         read_unlock(&tasklist_lock);
 245
 246                         break;
 247                 case IOPRIO_WHO_USER:
 248                         uid = make_kuid(current_user_ns(), who);
 249                         if (!who)
 250                                 user = current_user();
 251                         else
 252                                 user = find_user(uid);
 253
 254                         if (!user)
 255                                 break;
 256
 257                         for_each_process_thread(g, p) {
 258                                 if (!uid_eq(task_uid(p), user->uid) ||
 259                                     !task_pid_vnr(p))
 260                                         continue;
 261                                 tmpio = get_task_ioprio(p);
 262                                 if (tmpio < 0)
 263                                         continue;
 264                                 if (ret == -ESRCH)
 265                                         ret = tmpio;
 266                                 else
 267                                         ret = ioprio_best(ret, tmpio);
 268                         }
 269
 270                         if (who)
 271                                 free_uid(user);
 272                         break;
 273                 default:
 274                         ret = -EINVAL;
 275         }
 276
 277         rcu_read_unlock();
 278         return ret;
 279 }