CRED: Use RCU to access another task's creds and to release a task's own creds
[linux-2.6.git] / fs / ioprio.c
1 /*
2  * fs/ioprio.c
3  *
4  * Copyright (C) 2004 Jens Axboe <axboe@kernel.dk>
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 #include <linux/pid_namespace.h>
29
30 static int set_task_ioprio(struct task_struct *task, int ioprio)
31 {
32         int err;
33         struct io_context *ioc;
34         const struct cred *cred = current_cred(), *tcred;
35
36         rcu_read_lock();
37         tcred = __task_cred(task);
38         if (tcred->uid != cred->euid &&
39             tcred->uid != cred->uid && !capable(CAP_SYS_NICE)) {
40                 rcu_read_unlock();
41                 return -EPERM;
42         }
43         rcu_read_unlock();
44
45         err = security_task_setioprio(task, ioprio);
46         if (err)
47                 return err;
48
49         task_lock(task);
50         do {
51                 ioc = task->io_context;
52                 /* see wmb() in current_io_context() */
53                 smp_read_barrier_depends();
54                 if (ioc)
55                         break;
56
57                 ioc = alloc_io_context(GFP_ATOMIC, -1);
58                 if (!ioc) {
59                         err = -ENOMEM;
60                         break;
61                 }
62                 task->io_context = ioc;
63         } while (1);
64
65         if (!err) {
66                 ioc->ioprio = ioprio;
67                 ioc->ioprio_changed = 1;
68         }
69
70         task_unlock(task);
71         return err;
72 }
73
74 asmlinkage long sys_ioprio_set(int which, int who, int ioprio)
75 {
76         int class = IOPRIO_PRIO_CLASS(ioprio);
77         int data = IOPRIO_PRIO_DATA(ioprio);
78         struct task_struct *p, *g;
79         struct user_struct *user;
80         struct pid *pgrp;
81         int ret;
82
83         switch (class) {
84                 case IOPRIO_CLASS_RT:
85                         if (!capable(CAP_SYS_ADMIN))
86                                 return -EPERM;
87                         /* fall through, rt has prio field too */
88                 case IOPRIO_CLASS_BE:
89                         if (data >= IOPRIO_BE_NR || data < 0)
90                                 return -EINVAL;
91
92                         break;
93                 case IOPRIO_CLASS_IDLE:
94                         break;
95                 case IOPRIO_CLASS_NONE:
96                         if (data)
97                                 return -EINVAL;
98                         break;
99                 default:
100                         return -EINVAL;
101         }
102
103         ret = -ESRCH;
104         /*
105          * We want IOPRIO_WHO_PGRP/IOPRIO_WHO_USER to be "atomic",
106          * so we can't use rcu_read_lock(). See re-copy of ->ioprio
107          * in copy_process().
108          */
109         read_lock(&tasklist_lock);
110         switch (which) {
111                 case IOPRIO_WHO_PROCESS:
112                         if (!who)
113                                 p = current;
114                         else
115                                 p = find_task_by_vpid(who);
116                         if (p)
117                                 ret = set_task_ioprio(p, ioprio);
118                         break;
119                 case IOPRIO_WHO_PGRP:
120                         if (!who)
121                                 pgrp = task_pgrp(current);
122                         else
123                                 pgrp = find_vpid(who);
124                         do_each_pid_thread(pgrp, PIDTYPE_PGID, p) {
125                                 ret = set_task_ioprio(p, ioprio);
126                                 if (ret)
127                                         break;
128                         } while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
129                         break;
130                 case IOPRIO_WHO_USER:
131                         if (!who)
132                                 user = current_user();
133                         else
134                                 user = find_user(who);
135
136                         if (!user)
137                                 break;
138
139                         do_each_thread(g, p) {
140                                 if (__task_cred(p)->uid != who)
141                                         continue;
142                                 ret = set_task_ioprio(p, ioprio);
143                                 if (ret)
144                                         goto free_uid;
145                         } while_each_thread(g, p);
146 free_uid:
147                         if (who)
148                                 free_uid(user);
149                         break;
150                 default:
151                         ret = -EINVAL;
152         }
153
154         read_unlock(&tasklist_lock);
155         return ret;
156 }
157
158 static int get_task_ioprio(struct task_struct *p)
159 {
160         int ret;
161
162         ret = security_task_getioprio(p);
163         if (ret)
164                 goto out;
165         ret = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_NONE, IOPRIO_NORM);
166         if (p->io_context)
167                 ret = p->io_context->ioprio;
168 out:
169         return ret;
170 }
171
172 int ioprio_best(unsigned short aprio, unsigned short bprio)
173 {
174         unsigned short aclass = IOPRIO_PRIO_CLASS(aprio);
175         unsigned short bclass = IOPRIO_PRIO_CLASS(bprio);
176
177         if (aclass == IOPRIO_CLASS_NONE)
178                 aclass = IOPRIO_CLASS_BE;
179         if (bclass == IOPRIO_CLASS_NONE)
180                 bclass = IOPRIO_CLASS_BE;
181
182         if (aclass == bclass)
183                 return min(aprio, bprio);
184         if (aclass > bclass)
185                 return bprio;
186         else
187                 return aprio;
188 }
189
190 asmlinkage long sys_ioprio_get(int which, int who)
191 {
192         struct task_struct *g, *p;
193         struct user_struct *user;
194         struct pid *pgrp;
195         int ret = -ESRCH;
196         int tmpio;
197
198         read_lock(&tasklist_lock);
199         switch (which) {
200                 case IOPRIO_WHO_PROCESS:
201                         if (!who)
202                                 p = current;
203                         else
204                                 p = find_task_by_vpid(who);
205                         if (p)
206                                 ret = get_task_ioprio(p);
207                         break;
208                 case IOPRIO_WHO_PGRP:
209                         if (!who)
210                                 pgrp = task_pgrp(current);
211                         else
212                                 pgrp = find_vpid(who);
213                         do_each_pid_thread(pgrp, PIDTYPE_PGID, p) {
214                                 tmpio = get_task_ioprio(p);
215                                 if (tmpio < 0)
216                                         continue;
217                                 if (ret == -ESRCH)
218                                         ret = tmpio;
219                                 else
220                                         ret = ioprio_best(ret, tmpio);
221                         } while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
222                         break;
223                 case IOPRIO_WHO_USER:
224                         if (!who)
225                                 user = current_user();
226                         else
227                                 user = find_user(who);
228
229                         if (!user)
230                                 break;
231
232                         do_each_thread(g, p) {
233                                 if (__task_cred(p)->uid != user->uid)
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                         } while_each_thread(g, p);
243
244                         if (who)
245                                 free_uid(user);
246                         break;
247                 default:
248                         ret = -EINVAL;
249         }
250
251         read_unlock(&tasklist_lock);
252         return ret;
253 }
254