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
ioprio_check_cap(int ioprio)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
SYSCALL_DEFINE3(ioprio_set,int,which,int,who,int,ioprio)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 */
__get_task_ioprio(struct task_struct * p)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
get_task_ioprio(struct task_struct * p)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 */
get_task_raw_ioprio(struct task_struct * p)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
ioprio_best(unsigned short aprio,unsigned short bprio)205 static int ioprio_best(unsigned short aprio, unsigned short bprio)
206 {
207 return min(aprio, bprio);
208 }
209
SYSCALL_DEFINE2(ioprio_get,int,which,int,who)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