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 static int get_task_ioprio(struct task_struct *p) 143 { 144 int ret; 145 146 ret = security_task_getioprio(p); 147 if (ret) 148 goto out; 149 task_lock(p); 150 ret = __get_task_ioprio(p); 151 task_unlock(p); 152 out: 153 return ret; 154 } 155 156 /* 157 * Return raw IO priority value as set by userspace. We use this for 158 * ioprio_get(pid, IOPRIO_WHO_PROCESS) so that we keep historical behavior and 159 * also so that userspace can distinguish unset IO priority (which just gets 160 * overriden based on task's nice value) from IO priority set to some value. 161 */ 162 static int get_task_raw_ioprio(struct task_struct *p) 163 { 164 int ret; 165 166 ret = security_task_getioprio(p); 167 if (ret) 168 goto out; 169 task_lock(p); 170 if (p->io_context) 171 ret = p->io_context->ioprio; 172 else 173 ret = IOPRIO_DEFAULT; 174 task_unlock(p); 175 out: 176 return ret; 177 } 178 179 static int ioprio_best(unsigned short aprio, unsigned short bprio) 180 { 181 return min(aprio, bprio); 182 } 183 184 SYSCALL_DEFINE2(ioprio_get, int, which, int, who) 185 { 186 struct task_struct *g, *p; 187 struct user_struct *user; 188 struct pid *pgrp; 189 kuid_t uid; 190 int ret = -ESRCH; 191 int tmpio; 192 193 rcu_read_lock(); 194 switch (which) { 195 case IOPRIO_WHO_PROCESS: 196 if (!who) 197 p = current; 198 else 199 p = find_task_by_vpid(who); 200 if (p) 201 ret = get_task_raw_ioprio(p); 202 break; 203 case IOPRIO_WHO_PGRP: 204 if (!who) 205 pgrp = task_pgrp(current); 206 else 207 pgrp = find_vpid(who); 208 read_lock(&tasklist_lock); 209 do_each_pid_thread(pgrp, PIDTYPE_PGID, p) { 210 tmpio = get_task_ioprio(p); 211 if (tmpio < 0) 212 continue; 213 if (ret == -ESRCH) 214 ret = tmpio; 215 else 216 ret = ioprio_best(ret, tmpio); 217 } while_each_pid_thread(pgrp, PIDTYPE_PGID, p); 218 read_unlock(&tasklist_lock); 219 220 break; 221 case IOPRIO_WHO_USER: 222 uid = make_kuid(current_user_ns(), who); 223 if (!who) 224 user = current_user(); 225 else 226 user = find_user(uid); 227 228 if (!user) 229 break; 230 231 for_each_process_thread(g, p) { 232 if (!uid_eq(task_uid(p), user->uid) || 233 !task_pid_vnr(p)) 234 continue; 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 } 243 244 if (who) 245 free_uid(user); 246 break; 247 default: 248 ret = -EINVAL; 249 } 250 251 rcu_read_unlock(); 252 return ret; 253 } 254