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 } 280