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
 33int 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			break;
 50		case IOPRIO_CLASS_BE:
 51		case IOPRIO_CLASS_IDLE:
 52			break;
 53		case IOPRIO_CLASS_NONE:
 54			if (level)
 55				return -EINVAL;
 56			break;
 57		case IOPRIO_CLASS_INVALID:
 58		default:
 59			return -EINVAL;
 60	}
 61
 62	return 0;
 63}
 64
 65SYSCALL_DEFINE3(ioprio_set, int, which, int, who, int, ioprio)
 66{
 67	struct task_struct *p, *g;
 68	struct user_struct *user;
 69	struct pid *pgrp;
 70	kuid_t uid;
 71	int ret;
 72
 73	ret = ioprio_check_cap(ioprio);
 74	if (ret)
 75		return ret;
 76
 77	ret = -ESRCH;
 78	rcu_read_lock();
 79	switch (which) {
 80		case IOPRIO_WHO_PROCESS:
 81			if (!who)
 82				p = current;
 83			else
 84				p = find_task_by_vpid(who);
 85			if (p)
 86				ret = set_task_ioprio(p, ioprio);
 87			break;
 88		case IOPRIO_WHO_PGRP:
 89			if (!who)
 90				pgrp = task_pgrp(current);
 91			else
 92				pgrp = find_vpid(who);
 93
 94			read_lock(&tasklist_lock);
 95			do_each_pid_thread(pgrp, PIDTYPE_PGID, p) {
 96				ret = set_task_ioprio(p, ioprio);
 97				if (ret) {
 98					read_unlock(&tasklist_lock);
 99					goto out;
100				}
101			} while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
102			read_unlock(&tasklist_lock);
103
104			break;
105		case IOPRIO_WHO_USER:
106			uid = make_kuid(current_user_ns(), who);
107			if (!uid_valid(uid))
108				break;
109			if (!who)
110				user = current_user();
111			else
112				user = find_user(uid);
113
114			if (!user)
115				break;
116
117			for_each_process_thread(g, p) {
118				if (!uid_eq(task_uid(p), uid) ||
119				    !task_pid_vnr(p))
120					continue;
121				ret = set_task_ioprio(p, ioprio);
122				if (ret)
123					goto free_uid;
124			}
125free_uid:
126			if (who)
127				free_uid(user);
128			break;
129		default:
130			ret = -EINVAL;
131	}
132
133out:
134	rcu_read_unlock();
135	return ret;
136}
137
138static int get_task_ioprio(struct task_struct *p)
139{
140	int ret;
141
142	ret = security_task_getioprio(p);
143	if (ret)
144		goto out;
145	task_lock(p);
146	ret = __get_task_ioprio(p);
147	task_unlock(p);
148out:
149	return ret;
150}
151
152/*
153 * Return raw IO priority value as set by userspace. We use this for
154 * ioprio_get(pid, IOPRIO_WHO_PROCESS) so that we keep historical behavior and
155 * also so that userspace can distinguish unset IO priority (which just gets
156 * overriden based on task's nice value) from IO priority set to some value.
157 */
158static int get_task_raw_ioprio(struct task_struct *p)
159{
160	int ret;
161
162	ret = security_task_getioprio(p);
163	if (ret)
164		goto out;
165	task_lock(p);
166	if (p->io_context)
167		ret = p->io_context->ioprio;
168	else
169		ret = IOPRIO_DEFAULT;
170	task_unlock(p);
171out:
172	return ret;
173}
174
175static int ioprio_best(unsigned short aprio, unsigned short bprio)
176{
177	return min(aprio, bprio);
178}
179
180SYSCALL_DEFINE2(ioprio_get, int, which, int, who)
181{
182	struct task_struct *g, *p;
183	struct user_struct *user;
184	struct pid *pgrp;
185	kuid_t uid;
186	int ret = -ESRCH;
187	int tmpio;
188
189	rcu_read_lock();
190	switch (which) {
191		case IOPRIO_WHO_PROCESS:
192			if (!who)
193				p = current;
194			else
195				p = find_task_by_vpid(who);
196			if (p)
197				ret = get_task_raw_ioprio(p);
198			break;
199		case IOPRIO_WHO_PGRP:
200			if (!who)
201				pgrp = task_pgrp(current);
202			else
203				pgrp = find_vpid(who);
204			read_lock(&tasklist_lock);
205			do_each_pid_thread(pgrp, PIDTYPE_PGID, p) {
206				tmpio = get_task_ioprio(p);
207				if (tmpio < 0)
208					continue;
209				if (ret == -ESRCH)
210					ret = tmpio;
211				else
212					ret = ioprio_best(ret, tmpio);
213			} while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
214			read_unlock(&tasklist_lock);
215
216			break;
217		case IOPRIO_WHO_USER:
218			uid = make_kuid(current_user_ns(), who);
219			if (!who)
220				user = current_user();
221			else
222				user = find_user(uid);
223
224			if (!user)
225				break;
226
227			for_each_process_thread(g, p) {
228				if (!uid_eq(task_uid(p), user->uid) ||
229				    !task_pid_vnr(p))
230					continue;
231				tmpio = get_task_ioprio(p);
232				if (tmpio < 0)
233					continue;
234				if (ret == -ESRCH)
235					ret = tmpio;
236				else
237					ret = ioprio_best(ret, tmpio);
238			}
239
240			if (who)
241				free_uid(user);
242			break;
243		default:
244			ret = -EINVAL;
245	}
246
247	rcu_read_unlock();
248	return ret;
249}