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			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
 69SYSCALL_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			}
129free_uid:
130			if (who)
131				free_uid(user);
132			break;
133		default:
134			ret = -EINVAL;
135	}
136
137out:
138	rcu_read_unlock();
139	return ret;
140}
141
142static 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);
152out:
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 */
162static 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);
175out:
176	return ret;
177}
178
179static int ioprio_best(unsigned short aprio, unsigned short bprio)
180{
181	return min(aprio, bprio);
182}
183
184SYSCALL_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}