[PATCH] Fix current_io_context() vs set_task_ioprio() race
[linux-3.10.git] / fs / ioprio.c
1 /*
2  * fs/ioprio.c
3  *
4  * Copyright (C) 2004 Jens Axboe <axboe@suse.de>
5  *
6  * Helper functions for setting/querying io priorities of processes. The
7  * system calls closely mimmick getpriority/setpriority, see the man page for
8  * those. The prio argument is a composite of prio class and prio data, where
9  * the data argument has meaning within that class. The standard scheduling
10  * classes have 8 distinct prio levels, with 0 being the highest prio and 7
11  * being the lowest.
12  *
13  * IOW, setting BE scheduling class with prio 2 is done ala:
14  *
15  * unsigned int prio = (IOPRIO_CLASS_BE << IOPRIO_CLASS_SHIFT) | 2;
16  *
17  * ioprio_set(PRIO_PROCESS, pid, prio);
18  *
19  * See also Documentation/block/ioprio.txt
20  *
21  */
22 #include <linux/kernel.h>
23 #include <linux/ioprio.h>
24 #include <linux/blkdev.h>
25 #include <linux/capability.h>
26 #include <linux/syscalls.h>
27 #include <linux/security.h>
28
29 static int set_task_ioprio(struct task_struct *task, int ioprio)
30 {
31         int err;
32         struct io_context *ioc;
33
34         if (task->uid != current->euid &&
35             task->uid != current->uid && !capable(CAP_SYS_NICE))
36                 return -EPERM;
37
38         err = security_task_setioprio(task, ioprio);
39         if (err)
40                 return err;
41
42         task_lock(task);
43
44         task->ioprio = ioprio;
45
46         ioc = task->io_context;
47         /* see wmb() in current_io_context() */
48         smp_read_barrier_depends();
49
50         if (ioc && ioc->set_ioprio)
51                 ioc->set_ioprio(ioc, ioprio);
52
53         task_unlock(task);
54         return 0;
55 }
56
57 asmlinkage long sys_ioprio_set(int which, int who, int ioprio)
58 {
59         int class = IOPRIO_PRIO_CLASS(ioprio);
60         int data = IOPRIO_PRIO_DATA(ioprio);
61         struct task_struct *p, *g;
62         struct user_struct *user;
63         int ret;
64
65         switch (class) {
66                 case IOPRIO_CLASS_RT:
67                         if (!capable(CAP_SYS_ADMIN))
68                                 return -EPERM;
69                         /* fall through, rt has prio field too */
70                 case IOPRIO_CLASS_BE:
71                         if (data >= IOPRIO_BE_NR || data < 0)
72                                 return -EINVAL;
73
74                         break;
75                 case IOPRIO_CLASS_IDLE:
76                         if (!capable(CAP_SYS_ADMIN))
77                                 return -EPERM;
78                         break;
79                 default:
80                         return -EINVAL;
81         }
82
83         ret = -ESRCH;
84         read_lock_irq(&tasklist_lock);
85         switch (which) {
86                 case IOPRIO_WHO_PROCESS:
87                         if (!who)
88                                 p = current;
89                         else
90                                 p = find_task_by_pid(who);
91                         if (p)
92                                 ret = set_task_ioprio(p, ioprio);
93                         break;
94                 case IOPRIO_WHO_PGRP:
95                         if (!who)
96                                 who = process_group(current);
97                         do_each_task_pid(who, PIDTYPE_PGID, p) {
98                                 ret = set_task_ioprio(p, ioprio);
99                                 if (ret)
100                                         break;
101                         } while_each_task_pid(who, PIDTYPE_PGID, p);
102                         break;
103                 case IOPRIO_WHO_USER:
104                         if (!who)
105                                 user = current->user;
106                         else
107                                 user = find_user(who);
108
109                         if (!user)
110                                 break;
111
112                         do_each_thread(g, p) {
113                                 if (p->uid != who)
114                                         continue;
115                                 ret = set_task_ioprio(p, ioprio);
116                                 if (ret)
117                                         goto free_uid;
118                         } while_each_thread(g, p);
119 free_uid:
120                         if (who)
121                                 free_uid(user);
122                         break;
123                 default:
124                         ret = -EINVAL;
125         }
126
127         read_unlock_irq(&tasklist_lock);
128         return ret;
129 }
130
131 static int get_task_ioprio(struct task_struct *p)
132 {
133         int ret;
134
135         ret = security_task_getioprio(p);
136         if (ret)
137                 goto out;
138         ret = p->ioprio;
139 out:
140         return ret;
141 }
142
143 asmlinkage long sys_ioprio_get(int which, int who)
144 {
145         struct task_struct *g, *p;
146         struct user_struct *user;
147         int ret = -ESRCH;
148         int tmpio;
149
150         read_lock_irq(&tasklist_lock);
151         switch (which) {
152                 case IOPRIO_WHO_PROCESS:
153                         if (!who)
154                                 p = current;
155                         else
156                                 p = find_task_by_pid(who);
157                         if (p)
158                                 ret = get_task_ioprio(p);
159                         break;
160                 case IOPRIO_WHO_PGRP:
161                         if (!who)
162                                 who = process_group(current);
163                         do_each_task_pid(who, PIDTYPE_PGID, p) {
164                                 tmpio = get_task_ioprio(p);
165                                 if (tmpio < 0)
166                                         continue;
167                                 if (ret == -ESRCH)
168                                         ret = tmpio;
169                                 else
170                                         ret = ioprio_best(ret, tmpio);
171                         } while_each_task_pid(who, PIDTYPE_PGID, p);
172                         break;
173                 case IOPRIO_WHO_USER:
174                         if (!who)
175                                 user = current->user;
176                         else
177                                 user = find_user(who);
178
179                         if (!user)
180                                 break;
181
182                         do_each_thread(g, p) {
183                                 if (p->uid != user->uid)
184                                         continue;
185                                 tmpio = get_task_ioprio(p);
186                                 if (tmpio < 0)
187                                         continue;
188                                 if (ret == -ESRCH)
189                                         ret = tmpio;
190                                 else
191                                         ret = ioprio_best(ret, tmpio);
192                         } while_each_thread(g, p);
193
194                         if (who)
195                                 free_uid(user);
196                         break;
197                 default:
198                         ret = -EINVAL;
199         }
200
201         read_unlock_irq(&tasklist_lock);
202         return ret;
203 }
204