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