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 } 279