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/export.h>
26 #include <linux/ioprio.h>
27 #include <linux/cred.h>
28 #include <linux/blkdev.h>
29 #include <linux/capability.h>
30 #include <linux/sched/user.h>
31 #include <linux/sched/task.h>
32 #include <linux/syscalls.h>
33 #include <linux/security.h>
34 #include <linux/pid_namespace.h>
35
set_task_ioprio(struct task_struct * task,int ioprio)36 int set_task_ioprio(struct task_struct *task, int ioprio)
37 {
38 int err;
39 struct io_context *ioc;
40 const struct cred *cred = current_cred(), *tcred;
41
42 rcu_read_lock();
43 tcred = __task_cred(task);
44 if (!uid_eq(tcred->uid, cred->euid) &&
45 !uid_eq(tcred->uid, cred->uid) && !capable(CAP_SYS_NICE)) {
46 rcu_read_unlock();
47 return -EPERM;
48 }
49 rcu_read_unlock();
50
51 err = security_task_setioprio(task, ioprio);
52 if (err)
53 return err;
54
55 ioc = get_task_io_context(task, GFP_ATOMIC, NUMA_NO_NODE);
56 if (ioc) {
57 ioc->ioprio = ioprio;
58 put_io_context(ioc);
59 }
60
61 return err;
62 }
63 EXPORT_SYMBOL_GPL(set_task_ioprio);
64
ioprio_check_cap(int ioprio)65 int ioprio_check_cap(int ioprio)
66 {
67 int class = IOPRIO_PRIO_CLASS(ioprio);
68 int data = IOPRIO_PRIO_DATA(ioprio);
69
70 switch (class) {
71 case IOPRIO_CLASS_RT:
72 /*
73 * Originally this only checked for CAP_SYS_ADMIN,
74 * which was implicitly allowed for pid 0 by security
75 * modules such as SELinux. Make sure we check
76 * CAP_SYS_ADMIN first to avoid a denial/avc for
77 * possibly missing CAP_SYS_NICE permission.
78 */
79 if (!capable(CAP_SYS_ADMIN) && !capable(CAP_SYS_NICE))
80 return -EPERM;
81 fallthrough;
82 /* rt has prio field too */
83 case IOPRIO_CLASS_BE:
84 if (data >= IOPRIO_BE_NR || data < 0)
85 return -EINVAL;
86
87 break;
88 case IOPRIO_CLASS_IDLE:
89 break;
90 case IOPRIO_CLASS_NONE:
91 if (data)
92 return -EINVAL;
93 break;
94 default:
95 return -EINVAL;
96 }
97
98 return 0;
99 }
100
SYSCALL_DEFINE3(ioprio_set,int,which,int,who,int,ioprio)101 SYSCALL_DEFINE3(ioprio_set, int, which, int, who, int, ioprio)
102 {
103 struct task_struct *p, *g;
104 struct user_struct *user;
105 struct pid *pgrp;
106 kuid_t uid;
107 int ret;
108
109 ret = ioprio_check_cap(ioprio);
110 if (ret)
111 return ret;
112
113 ret = -ESRCH;
114 rcu_read_lock();
115 switch (which) {
116 case IOPRIO_WHO_PROCESS:
117 if (!who)
118 p = current;
119 else
120 p = find_task_by_vpid(who);
121 if (p)
122 ret = set_task_ioprio(p, ioprio);
123 break;
124 case IOPRIO_WHO_PGRP:
125 if (!who)
126 pgrp = task_pgrp(current);
127 else
128 pgrp = find_vpid(who);
129 do_each_pid_thread(pgrp, PIDTYPE_PGID, p) {
130 ret = set_task_ioprio(p, ioprio);
131 if (ret)
132 break;
133 } while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
134 break;
135 case IOPRIO_WHO_USER:
136 uid = make_kuid(current_user_ns(), who);
137 if (!uid_valid(uid))
138 break;
139 if (!who)
140 user = current_user();
141 else
142 user = find_user(uid);
143
144 if (!user)
145 break;
146
147 for_each_process_thread(g, p) {
148 if (!uid_eq(task_uid(p), uid) ||
149 !task_pid_vnr(p))
150 continue;
151 ret = set_task_ioprio(p, ioprio);
152 if (ret)
153 goto free_uid;
154 }
155 free_uid:
156 if (who)
157 free_uid(user);
158 break;
159 default:
160 ret = -EINVAL;
161 }
162
163 rcu_read_unlock();
164 return ret;
165 }
166
get_task_ioprio(struct task_struct * p)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 ret = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_NONE, IOPRIO_NORM);
175 task_lock(p);
176 if (p->io_context)
177 ret = p->io_context->ioprio;
178 task_unlock(p);
179 out:
180 return ret;
181 }
182
ioprio_best(unsigned short aprio,unsigned short bprio)183 int ioprio_best(unsigned short aprio, unsigned short bprio)
184 {
185 if (!ioprio_valid(aprio))
186 aprio = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_BE, IOPRIO_NORM);
187 if (!ioprio_valid(bprio))
188 bprio = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_BE, IOPRIO_NORM);
189
190 return min(aprio, bprio);
191 }
192
SYSCALL_DEFINE2(ioprio_get,int,which,int,who)193 SYSCALL_DEFINE2(ioprio_get, int, which, int, who)
194 {
195 struct task_struct *g, *p;
196 struct user_struct *user;
197 struct pid *pgrp;
198 kuid_t uid;
199 int ret = -ESRCH;
200 int tmpio;
201
202 rcu_read_lock();
203 switch (which) {
204 case IOPRIO_WHO_PROCESS:
205 if (!who)
206 p = current;
207 else
208 p = find_task_by_vpid(who);
209 if (p)
210 ret = get_task_ioprio(p);
211 break;
212 case IOPRIO_WHO_PGRP:
213 if (!who)
214 pgrp = task_pgrp(current);
215 else
216 pgrp = find_vpid(who);
217 read_lock(&tasklist_lock);
218 do_each_pid_thread(pgrp, PIDTYPE_PGID, p) {
219 tmpio = get_task_ioprio(p);
220 if (tmpio < 0)
221 continue;
222 if (ret == -ESRCH)
223 ret = tmpio;
224 else
225 ret = ioprio_best(ret, tmpio);
226 } while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
227 read_unlock(&tasklist_lock);
228
229 break;
230 case IOPRIO_WHO_USER:
231 uid = make_kuid(current_user_ns(), who);
232 if (!who)
233 user = current_user();
234 else
235 user = find_user(uid);
236
237 if (!user)
238 break;
239
240 for_each_process_thread(g, p) {
241 if (!uid_eq(task_uid(p), user->uid) ||
242 !task_pid_vnr(p))
243 continue;
244 tmpio = get_task_ioprio(p);
245 if (tmpio < 0)
246 continue;
247 if (ret == -ESRCH)
248 ret = tmpio;
249 else
250 ret = ioprio_best(ret, tmpio);
251 }
252
253 if (who)
254 free_uid(user);
255 break;
256 default:
257 ret = -EINVAL;
258 }
259
260 rcu_read_unlock();
261 return ret;
262 }
263