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_NR_LEVELS || data < 0)
85 return -EINVAL;
86 break;
87 case IOPRIO_CLASS_IDLE:
88 break;
89 case IOPRIO_CLASS_NONE:
90 if (data)
91 return -EINVAL;
92 break;
93 default:
94 return -EINVAL;
95 }
96
97 return 0;
98 }
99
SYSCALL_DEFINE3(ioprio_set,int,which,int,who,int,ioprio)100 SYSCALL_DEFINE3(ioprio_set, int, which, int, who, int, ioprio)
101 {
102 struct task_struct *p, *g;
103 struct user_struct *user;
104 struct pid *pgrp;
105 kuid_t uid;
106 int ret;
107
108 ret = ioprio_check_cap(ioprio);
109 if (ret)
110 return ret;
111
112 ret = -ESRCH;
113 rcu_read_lock();
114 switch (which) {
115 case IOPRIO_WHO_PROCESS:
116 if (!who)
117 p = current;
118 else
119 p = find_task_by_vpid(who);
120 if (p)
121 ret = set_task_ioprio(p, ioprio);
122 break;
123 case IOPRIO_WHO_PGRP:
124 if (!who)
125 pgrp = task_pgrp(current);
126 else
127 pgrp = find_vpid(who);
128
129 read_lock(&tasklist_lock);
130 do_each_pid_thread(pgrp, PIDTYPE_PGID, p) {
131 ret = set_task_ioprio(p, ioprio);
132 if (ret) {
133 read_unlock(&tasklist_lock);
134 goto out;
135 }
136 } while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
137 read_unlock(&tasklist_lock);
138
139 break;
140 case IOPRIO_WHO_USER:
141 uid = make_kuid(current_user_ns(), who);
142 if (!uid_valid(uid))
143 break;
144 if (!who)
145 user = current_user();
146 else
147 user = find_user(uid);
148
149 if (!user)
150 break;
151
152 for_each_process_thread(g, p) {
153 if (!uid_eq(task_uid(p), uid) ||
154 !task_pid_vnr(p))
155 continue;
156 ret = set_task_ioprio(p, ioprio);
157 if (ret)
158 goto free_uid;
159 }
160 free_uid:
161 if (who)
162 free_uid(user);
163 break;
164 default:
165 ret = -EINVAL;
166 }
167
168 out:
169 rcu_read_unlock();
170 return ret;
171 }
172
get_task_ioprio(struct task_struct * p)173 static int get_task_ioprio(struct task_struct *p)
174 {
175 int ret;
176
177 ret = security_task_getioprio(p);
178 if (ret)
179 goto out;
180 ret = IOPRIO_DEFAULT;
181 task_lock(p);
182 if (p->io_context)
183 ret = p->io_context->ioprio;
184 task_unlock(p);
185 out:
186 return ret;
187 }
188
ioprio_best(unsigned short aprio,unsigned short bprio)189 int ioprio_best(unsigned short aprio, unsigned short bprio)
190 {
191 if (!ioprio_valid(aprio))
192 aprio = IOPRIO_DEFAULT;
193 if (!ioprio_valid(bprio))
194 bprio = IOPRIO_DEFAULT;
195
196 return min(aprio, bprio);
197 }
198
SYSCALL_DEFINE2(ioprio_get,int,which,int,who)199 SYSCALL_DEFINE2(ioprio_get, int, which, int, who)
200 {
201 struct task_struct *g, *p;
202 struct user_struct *user;
203 struct pid *pgrp;
204 kuid_t uid;
205 int ret = -ESRCH;
206 int tmpio;
207
208 rcu_read_lock();
209 switch (which) {
210 case IOPRIO_WHO_PROCESS:
211 if (!who)
212 p = current;
213 else
214 p = find_task_by_vpid(who);
215 if (p)
216 ret = get_task_ioprio(p);
217 break;
218 case IOPRIO_WHO_PGRP:
219 if (!who)
220 pgrp = task_pgrp(current);
221 else
222 pgrp = find_vpid(who);
223 read_lock(&tasklist_lock);
224 do_each_pid_thread(pgrp, PIDTYPE_PGID, p) {
225 tmpio = get_task_ioprio(p);
226 if (tmpio < 0)
227 continue;
228 if (ret == -ESRCH)
229 ret = tmpio;
230 else
231 ret = ioprio_best(ret, tmpio);
232 } while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
233 read_unlock(&tasklist_lock);
234
235 break;
236 case IOPRIO_WHO_USER:
237 uid = make_kuid(current_user_ns(), who);
238 if (!who)
239 user = current_user();
240 else
241 user = find_user(uid);
242
243 if (!user)
244 break;
245
246 for_each_process_thread(g, p) {
247 if (!uid_eq(task_uid(p), user->uid) ||
248 !task_pid_vnr(p))
249 continue;
250 tmpio = get_task_ioprio(p);
251 if (tmpio < 0)
252 continue;
253 if (ret == -ESRCH)
254 ret = tmpio;
255 else
256 ret = ioprio_best(ret, tmpio);
257 }
258
259 if (who)
260 free_uid(user);
261 break;
262 default:
263 ret = -EINVAL;
264 }
265
266 rcu_read_unlock();
267 return ret;
268 }
269