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 static 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);
152 out:
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 */
162 static 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);
175 out:
176 return ret;
177 }
178
179 static int ioprio_best(unsigned short aprio, unsigned short bprio)
180 {
181 return min(aprio, bprio);
182 }
183
184 SYSCALL_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 }
254
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