Root/security/device_cgroup.c

1/*
2 * device_cgroup.c - device cgroup subsystem
3 *
4 * Copyright 2007 IBM Corp
5 */
6
7#include <linux/device_cgroup.h>
8#include <linux/cgroup.h>
9#include <linux/ctype.h>
10#include <linux/list.h>
11#include <linux/uaccess.h>
12#include <linux/seq_file.h>
13#include <linux/slab.h>
14#include <linux/rcupdate.h>
15#include <linux/mutex.h>
16
17#define ACC_MKNOD 1
18#define ACC_READ 2
19#define ACC_WRITE 4
20#define ACC_MASK (ACC_MKNOD | ACC_READ | ACC_WRITE)
21
22#define DEV_BLOCK 1
23#define DEV_CHAR 2
24#define DEV_ALL 4 /* this represents all devices */
25
26static DEFINE_MUTEX(devcgroup_mutex);
27
28/*
29 * whitelist locking rules:
30 * hold devcgroup_mutex for update/read.
31 * hold rcu_read_lock() for read.
32 */
33
34struct dev_whitelist_item {
35    u32 major, minor;
36    short type;
37    short access;
38    struct list_head list;
39    struct rcu_head rcu;
40};
41
42struct dev_cgroup {
43    struct cgroup_subsys_state css;
44    struct list_head whitelist;
45};
46
47static inline struct dev_cgroup *css_to_devcgroup(struct cgroup_subsys_state *s)
48{
49    return container_of(s, struct dev_cgroup, css);
50}
51
52static inline struct dev_cgroup *cgroup_to_devcgroup(struct cgroup *cgroup)
53{
54    return css_to_devcgroup(cgroup_subsys_state(cgroup, devices_subsys_id));
55}
56
57static inline struct dev_cgroup *task_devcgroup(struct task_struct *task)
58{
59    return css_to_devcgroup(task_subsys_state(task, devices_subsys_id));
60}
61
62struct cgroup_subsys devices_subsys;
63
64static int devcgroup_can_attach(struct cgroup *new_cgrp,
65                struct cgroup_taskset *set)
66{
67    struct task_struct *task = cgroup_taskset_first(set);
68
69    if (current != task && !capable(CAP_SYS_ADMIN))
70        return -EPERM;
71    return 0;
72}
73
74/*
75 * called under devcgroup_mutex
76 */
77static int dev_whitelist_copy(struct list_head *dest, struct list_head *orig)
78{
79    struct dev_whitelist_item *wh, *tmp, *new;
80
81    list_for_each_entry(wh, orig, list) {
82        new = kmemdup(wh, sizeof(*wh), GFP_KERNEL);
83        if (!new)
84            goto free_and_exit;
85        list_add_tail(&new->list, dest);
86    }
87
88    return 0;
89
90free_and_exit:
91    list_for_each_entry_safe(wh, tmp, dest, list) {
92        list_del(&wh->list);
93        kfree(wh);
94    }
95    return -ENOMEM;
96}
97
98/* Stupid prototype - don't bother combining existing entries */
99/*
100 * called under devcgroup_mutex
101 */
102static int dev_whitelist_add(struct dev_cgroup *dev_cgroup,
103            struct dev_whitelist_item *wh)
104{
105    struct dev_whitelist_item *whcopy, *walk;
106
107    whcopy = kmemdup(wh, sizeof(*wh), GFP_KERNEL);
108    if (!whcopy)
109        return -ENOMEM;
110
111    list_for_each_entry(walk, &dev_cgroup->whitelist, list) {
112        if (walk->type != wh->type)
113            continue;
114        if (walk->major != wh->major)
115            continue;
116        if (walk->minor != wh->minor)
117            continue;
118
119        walk->access |= wh->access;
120        kfree(whcopy);
121        whcopy = NULL;
122    }
123
124    if (whcopy != NULL)
125        list_add_tail_rcu(&whcopy->list, &dev_cgroup->whitelist);
126    return 0;
127}
128
129/*
130 * called under devcgroup_mutex
131 */
132static void dev_whitelist_rm(struct dev_cgroup *dev_cgroup,
133            struct dev_whitelist_item *wh)
134{
135    struct dev_whitelist_item *walk, *tmp;
136
137    list_for_each_entry_safe(walk, tmp, &dev_cgroup->whitelist, list) {
138        if (walk->type == DEV_ALL)
139            goto remove;
140        if (walk->type != wh->type)
141            continue;
142        if (walk->major != ~0 && walk->major != wh->major)
143            continue;
144        if (walk->minor != ~0 && walk->minor != wh->minor)
145            continue;
146
147remove:
148        walk->access &= ~wh->access;
149        if (!walk->access) {
150            list_del_rcu(&walk->list);
151            kfree_rcu(walk, rcu);
152        }
153    }
154}
155
156/*
157 * called from kernel/cgroup.c with cgroup_lock() held.
158 */
159static struct cgroup_subsys_state *devcgroup_create(struct cgroup *cgroup)
160{
161    struct dev_cgroup *dev_cgroup, *parent_dev_cgroup;
162    struct cgroup *parent_cgroup;
163    int ret;
164
165    dev_cgroup = kzalloc(sizeof(*dev_cgroup), GFP_KERNEL);
166    if (!dev_cgroup)
167        return ERR_PTR(-ENOMEM);
168    INIT_LIST_HEAD(&dev_cgroup->whitelist);
169    parent_cgroup = cgroup->parent;
170
171    if (parent_cgroup == NULL) {
172        struct dev_whitelist_item *wh;
173        wh = kmalloc(sizeof(*wh), GFP_KERNEL);
174        if (!wh) {
175            kfree(dev_cgroup);
176            return ERR_PTR(-ENOMEM);
177        }
178        wh->minor = wh->major = ~0;
179        wh->type = DEV_ALL;
180        wh->access = ACC_MASK;
181        list_add(&wh->list, &dev_cgroup->whitelist);
182    } else {
183        parent_dev_cgroup = cgroup_to_devcgroup(parent_cgroup);
184        mutex_lock(&devcgroup_mutex);
185        ret = dev_whitelist_copy(&dev_cgroup->whitelist,
186                &parent_dev_cgroup->whitelist);
187        mutex_unlock(&devcgroup_mutex);
188        if (ret) {
189            kfree(dev_cgroup);
190            return ERR_PTR(ret);
191        }
192    }
193
194    return &dev_cgroup->css;
195}
196
197static void devcgroup_destroy(struct cgroup *cgroup)
198{
199    struct dev_cgroup *dev_cgroup;
200    struct dev_whitelist_item *wh, *tmp;
201
202    dev_cgroup = cgroup_to_devcgroup(cgroup);
203    list_for_each_entry_safe(wh, tmp, &dev_cgroup->whitelist, list) {
204        list_del(&wh->list);
205        kfree(wh);
206    }
207    kfree(dev_cgroup);
208}
209
210#define DEVCG_ALLOW 1
211#define DEVCG_DENY 2
212#define DEVCG_LIST 3
213
214#define MAJMINLEN 13
215#define ACCLEN 4
216
217static void set_access(char *acc, short access)
218{
219    int idx = 0;
220    memset(acc, 0, ACCLEN);
221    if (access & ACC_READ)
222        acc[idx++] = 'r';
223    if (access & ACC_WRITE)
224        acc[idx++] = 'w';
225    if (access & ACC_MKNOD)
226        acc[idx++] = 'm';
227}
228
229static char type_to_char(short type)
230{
231    if (type == DEV_ALL)
232        return 'a';
233    if (type == DEV_CHAR)
234        return 'c';
235    if (type == DEV_BLOCK)
236        return 'b';
237    return 'X';
238}
239
240static void set_majmin(char *str, unsigned m)
241{
242    if (m == ~0)
243        strcpy(str, "*");
244    else
245        sprintf(str, "%u", m);
246}
247
248static int devcgroup_seq_read(struct cgroup *cgroup, struct cftype *cft,
249                struct seq_file *m)
250{
251    struct dev_cgroup *devcgroup = cgroup_to_devcgroup(cgroup);
252    struct dev_whitelist_item *wh;
253    char maj[MAJMINLEN], min[MAJMINLEN], acc[ACCLEN];
254
255    rcu_read_lock();
256    list_for_each_entry_rcu(wh, &devcgroup->whitelist, list) {
257        set_access(acc, wh->access);
258        set_majmin(maj, wh->major);
259        set_majmin(min, wh->minor);
260        seq_printf(m, "%c %s:%s %s\n", type_to_char(wh->type),
261               maj, min, acc);
262    }
263    rcu_read_unlock();
264
265    return 0;
266}
267
268/*
269 * may_access_whitelist:
270 * does the access granted to dev_cgroup c contain the access
271 * requested in whitelist item refwh.
272 * return 1 if yes, 0 if no.
273 * call with devcgroup_mutex held
274 */
275static int may_access_whitelist(struct dev_cgroup *c,
276                       struct dev_whitelist_item *refwh)
277{
278    struct dev_whitelist_item *whitem;
279
280    list_for_each_entry(whitem, &c->whitelist, list) {
281        if (whitem->type & DEV_ALL)
282            return 1;
283        if ((refwh->type & DEV_BLOCK) && !(whitem->type & DEV_BLOCK))
284            continue;
285        if ((refwh->type & DEV_CHAR) && !(whitem->type & DEV_CHAR))
286            continue;
287        if (whitem->major != ~0 && whitem->major != refwh->major)
288            continue;
289        if (whitem->minor != ~0 && whitem->minor != refwh->minor)
290            continue;
291        if (refwh->access & (~whitem->access))
292            continue;
293        return 1;
294    }
295    return 0;
296}
297
298/*
299 * parent_has_perm:
300 * when adding a new allow rule to a device whitelist, the rule
301 * must be allowed in the parent device
302 */
303static int parent_has_perm(struct dev_cgroup *childcg,
304                  struct dev_whitelist_item *wh)
305{
306    struct cgroup *pcg = childcg->css.cgroup->parent;
307    struct dev_cgroup *parent;
308
309    if (!pcg)
310        return 1;
311    parent = cgroup_to_devcgroup(pcg);
312    return may_access_whitelist(parent, wh);
313}
314
315/*
316 * Modify the whitelist using allow/deny rules.
317 * CAP_SYS_ADMIN is needed for this. It's at least separate from CAP_MKNOD
318 * so we can give a container CAP_MKNOD to let it create devices but not
319 * modify the whitelist.
320 * It seems likely we'll want to add a CAP_CONTAINER capability to allow
321 * us to also grant CAP_SYS_ADMIN to containers without giving away the
322 * device whitelist controls, but for now we'll stick with CAP_SYS_ADMIN
323 *
324 * Taking rules away is always allowed (given CAP_SYS_ADMIN). Granting
325 * new access is only allowed if you're in the top-level cgroup, or your
326 * parent cgroup has the access you're asking for.
327 */
328static int devcgroup_update_access(struct dev_cgroup *devcgroup,
329                   int filetype, const char *buffer)
330{
331    const char *b;
332    char *endp;
333    int count;
334    struct dev_whitelist_item wh;
335
336    if (!capable(CAP_SYS_ADMIN))
337        return -EPERM;
338
339    memset(&wh, 0, sizeof(wh));
340    b = buffer;
341
342    switch (*b) {
343    case 'a':
344        wh.type = DEV_ALL;
345        wh.access = ACC_MASK;
346        wh.major = ~0;
347        wh.minor = ~0;
348        goto handle;
349    case 'b':
350        wh.type = DEV_BLOCK;
351        break;
352    case 'c':
353        wh.type = DEV_CHAR;
354        break;
355    default:
356        return -EINVAL;
357    }
358    b++;
359    if (!isspace(*b))
360        return -EINVAL;
361    b++;
362    if (*b == '*') {
363        wh.major = ~0;
364        b++;
365    } else if (isdigit(*b)) {
366        wh.major = simple_strtoul(b, &endp, 10);
367        b = endp;
368    } else {
369        return -EINVAL;
370    }
371    if (*b != ':')
372        return -EINVAL;
373    b++;
374
375    /* read minor */
376    if (*b == '*') {
377        wh.minor = ~0;
378        b++;
379    } else if (isdigit(*b)) {
380        wh.minor = simple_strtoul(b, &endp, 10);
381        b = endp;
382    } else {
383        return -EINVAL;
384    }
385    if (!isspace(*b))
386        return -EINVAL;
387    for (b++, count = 0; count < 3; count++, b++) {
388        switch (*b) {
389        case 'r':
390            wh.access |= ACC_READ;
391            break;
392        case 'w':
393            wh.access |= ACC_WRITE;
394            break;
395        case 'm':
396            wh.access |= ACC_MKNOD;
397            break;
398        case '\n':
399        case '\0':
400            count = 3;
401            break;
402        default:
403            return -EINVAL;
404        }
405    }
406
407handle:
408    switch (filetype) {
409    case DEVCG_ALLOW:
410        if (!parent_has_perm(devcgroup, &wh))
411            return -EPERM;
412        return dev_whitelist_add(devcgroup, &wh);
413    case DEVCG_DENY:
414        dev_whitelist_rm(devcgroup, &wh);
415        break;
416    default:
417        return -EINVAL;
418    }
419    return 0;
420}
421
422static int devcgroup_access_write(struct cgroup *cgrp, struct cftype *cft,
423                  const char *buffer)
424{
425    int retval;
426
427    mutex_lock(&devcgroup_mutex);
428    retval = devcgroup_update_access(cgroup_to_devcgroup(cgrp),
429                     cft->private, buffer);
430    mutex_unlock(&devcgroup_mutex);
431    return retval;
432}
433
434static struct cftype dev_cgroup_files[] = {
435    {
436        .name = "allow",
437        .write_string = devcgroup_access_write,
438        .private = DEVCG_ALLOW,
439    },
440    {
441        .name = "deny",
442        .write_string = devcgroup_access_write,
443        .private = DEVCG_DENY,
444    },
445    {
446        .name = "list",
447        .read_seq_string = devcgroup_seq_read,
448        .private = DEVCG_LIST,
449    },
450    { } /* terminate */
451};
452
453struct cgroup_subsys devices_subsys = {
454    .name = "devices",
455    .can_attach = devcgroup_can_attach,
456    .create = devcgroup_create,
457    .destroy = devcgroup_destroy,
458    .subsys_id = devices_subsys_id,
459    .base_cftypes = dev_cgroup_files,
460};
461
462int __devcgroup_inode_permission(struct inode *inode, int mask)
463{
464    struct dev_cgroup *dev_cgroup;
465    struct dev_whitelist_item *wh;
466
467    rcu_read_lock();
468
469    dev_cgroup = task_devcgroup(current);
470
471    list_for_each_entry_rcu(wh, &dev_cgroup->whitelist, list) {
472        if (wh->type & DEV_ALL)
473            goto found;
474        if ((wh->type & DEV_BLOCK) && !S_ISBLK(inode->i_mode))
475            continue;
476        if ((wh->type & DEV_CHAR) && !S_ISCHR(inode->i_mode))
477            continue;
478        if (wh->major != ~0 && wh->major != imajor(inode))
479            continue;
480        if (wh->minor != ~0 && wh->minor != iminor(inode))
481            continue;
482
483        if ((mask & MAY_WRITE) && !(wh->access & ACC_WRITE))
484            continue;
485        if ((mask & MAY_READ) && !(wh->access & ACC_READ))
486            continue;
487found:
488        rcu_read_unlock();
489        return 0;
490    }
491
492    rcu_read_unlock();
493
494    return -EPERM;
495}
496
497int devcgroup_inode_mknod(int mode, dev_t dev)
498{
499    struct dev_cgroup *dev_cgroup;
500    struct dev_whitelist_item *wh;
501
502    if (!S_ISBLK(mode) && !S_ISCHR(mode))
503        return 0;
504
505    rcu_read_lock();
506
507    dev_cgroup = task_devcgroup(current);
508
509    list_for_each_entry_rcu(wh, &dev_cgroup->whitelist, list) {
510        if (wh->type & DEV_ALL)
511            goto found;
512        if ((wh->type & DEV_BLOCK) && !S_ISBLK(mode))
513            continue;
514        if ((wh->type & DEV_CHAR) && !S_ISCHR(mode))
515            continue;
516        if (wh->major != ~0 && wh->major != MAJOR(dev))
517            continue;
518        if (wh->minor != ~0 && wh->minor != MINOR(dev))
519            continue;
520
521        if (!(wh->access & ACC_MKNOD))
522            continue;
523found:
524        rcu_read_unlock();
525        return 0;
526    }
527
528    rcu_read_unlock();
529
530    return -EPERM;
531}
532

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