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
  36 int 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 }
  63 EXPORT_SYMBOL_GPL(set_task_ioprio);
  64
  65 int 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
 100 SYSCALL_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                         }
 160 free_uid:
 161                         if (who)
 162                                 free_uid(user);
 163                         break;
 164                 default:
 165                         ret = -EINVAL;
 166         }
 167
 168 out:
 169         rcu_read_unlock();
 170         return ret;
 171 }
 172
 173 static 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);
 185 out:
 186         return ret;
 187 }
 188
 189 int 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
 199 SYSCALL_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 }