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_subsys *ss,
65        struct cgroup *new_cgroup, struct task_struct *task,
66        bool threadgroup)
67{
68    if (current != task && !capable(CAP_SYS_ADMIN))
69            return -EPERM;
70
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
129static void whitelist_item_free(struct rcu_head *rcu)
130{
131    struct dev_whitelist_item *item;
132
133    item = container_of(rcu, struct dev_whitelist_item, rcu);
134    kfree(item);
135}
136
137/*
138 * called under devcgroup_mutex
139 */
140static void dev_whitelist_rm(struct dev_cgroup *dev_cgroup,
141            struct dev_whitelist_item *wh)
142{
143    struct dev_whitelist_item *walk, *tmp;
144
145    list_for_each_entry_safe(walk, tmp, &dev_cgroup->whitelist, list) {
146        if (walk->type == DEV_ALL)
147            goto remove;
148        if (walk->type != wh->type)
149            continue;
150        if (walk->major != ~0 && walk->major != wh->major)
151            continue;
152        if (walk->minor != ~0 && walk->minor != wh->minor)
153            continue;
154
155remove:
156        walk->access &= ~wh->access;
157        if (!walk->access) {
158            list_del_rcu(&walk->list);
159            call_rcu(&walk->rcu, whitelist_item_free);
160        }
161    }
162}
163
164/*
165 * called from kernel/cgroup.c with cgroup_lock() held.
166 */
167static struct cgroup_subsys_state *devcgroup_create(struct cgroup_subsys *ss,
168                        struct cgroup *cgroup)
169{
170    struct dev_cgroup *dev_cgroup, *parent_dev_cgroup;
171    struct cgroup *parent_cgroup;
172    int ret;
173
174    dev_cgroup = kzalloc(sizeof(*dev_cgroup), GFP_KERNEL);
175    if (!dev_cgroup)
176        return ERR_PTR(-ENOMEM);
177    INIT_LIST_HEAD(&dev_cgroup->whitelist);
178    parent_cgroup = cgroup->parent;
179
180    if (parent_cgroup == NULL) {
181        struct dev_whitelist_item *wh;
182        wh = kmalloc(sizeof(*wh), GFP_KERNEL);
183        if (!wh) {
184            kfree(dev_cgroup);
185            return ERR_PTR(-ENOMEM);
186        }
187        wh->minor = wh->major = ~0;
188        wh->type = DEV_ALL;
189        wh->access = ACC_MASK;
190        list_add(&wh->list, &dev_cgroup->whitelist);
191    } else {
192        parent_dev_cgroup = cgroup_to_devcgroup(parent_cgroup);
193        mutex_lock(&devcgroup_mutex);
194        ret = dev_whitelist_copy(&dev_cgroup->whitelist,
195                &parent_dev_cgroup->whitelist);
196        mutex_unlock(&devcgroup_mutex);
197        if (ret) {
198            kfree(dev_cgroup);
199            return ERR_PTR(ret);
200        }
201    }
202
203    return &dev_cgroup->css;
204}
205
206static void devcgroup_destroy(struct cgroup_subsys *ss,
207            struct cgroup *cgroup)
208{
209    struct dev_cgroup *dev_cgroup;
210    struct dev_whitelist_item *wh, *tmp;
211
212    dev_cgroup = cgroup_to_devcgroup(cgroup);
213    list_for_each_entry_safe(wh, tmp, &dev_cgroup->whitelist, list) {
214        list_del(&wh->list);
215        kfree(wh);
216    }
217    kfree(dev_cgroup);
218}
219
220#define DEVCG_ALLOW 1
221#define DEVCG_DENY 2
222#define DEVCG_LIST 3
223
224#define MAJMINLEN 13
225#define ACCLEN 4
226
227static void set_access(char *acc, short access)
228{
229    int idx = 0;
230    memset(acc, 0, ACCLEN);
231    if (access & ACC_READ)
232        acc[idx++] = 'r';
233    if (access & ACC_WRITE)
234        acc[idx++] = 'w';
235    if (access & ACC_MKNOD)
236        acc[idx++] = 'm';
237}
238
239static char type_to_char(short type)
240{
241    if (type == DEV_ALL)
242        return 'a';
243    if (type == DEV_CHAR)
244        return 'c';
245    if (type == DEV_BLOCK)
246        return 'b';
247    return 'X';
248}
249
250static void set_majmin(char *str, unsigned m)
251{
252    if (m == ~0)
253        strcpy(str, "*");
254    else
255        sprintf(str, "%u", m);
256}
257
258static int devcgroup_seq_read(struct cgroup *cgroup, struct cftype *cft,
259                struct seq_file *m)
260{
261    struct dev_cgroup *devcgroup = cgroup_to_devcgroup(cgroup);
262    struct dev_whitelist_item *wh;
263    char maj[MAJMINLEN], min[MAJMINLEN], acc[ACCLEN];
264
265    rcu_read_lock();
266    list_for_each_entry_rcu(wh, &devcgroup->whitelist, list) {
267        set_access(acc, wh->access);
268        set_majmin(maj, wh->major);
269        set_majmin(min, wh->minor);
270        seq_printf(m, "%c %s:%s %s\n", type_to_char(wh->type),
271               maj, min, acc);
272    }
273    rcu_read_unlock();
274
275    return 0;
276}
277
278/*
279 * may_access_whitelist:
280 * does the access granted to dev_cgroup c contain the access
281 * requested in whitelist item refwh.
282 * return 1 if yes, 0 if no.
283 * call with devcgroup_mutex held
284 */
285static int may_access_whitelist(struct dev_cgroup *c,
286                       struct dev_whitelist_item *refwh)
287{
288    struct dev_whitelist_item *whitem;
289
290    list_for_each_entry(whitem, &c->whitelist, list) {
291        if (whitem->type & DEV_ALL)
292            return 1;
293        if ((refwh->type & DEV_BLOCK) && !(whitem->type & DEV_BLOCK))
294            continue;
295        if ((refwh->type & DEV_CHAR) && !(whitem->type & DEV_CHAR))
296            continue;
297        if (whitem->major != ~0 && whitem->major != refwh->major)
298            continue;
299        if (whitem->minor != ~0 && whitem->minor != refwh->minor)
300            continue;
301        if (refwh->access & (~whitem->access))
302            continue;
303        return 1;
304    }
305    return 0;
306}
307
308/*
309 * parent_has_perm:
310 * when adding a new allow rule to a device whitelist, the rule
311 * must be allowed in the parent device
312 */
313static int parent_has_perm(struct dev_cgroup *childcg,
314                  struct dev_whitelist_item *wh)
315{
316    struct cgroup *pcg = childcg->css.cgroup->parent;
317    struct dev_cgroup *parent;
318
319    if (!pcg)
320        return 1;
321    parent = cgroup_to_devcgroup(pcg);
322    return may_access_whitelist(parent, wh);
323}
324
325/*
326 * Modify the whitelist using allow/deny rules.
327 * CAP_SYS_ADMIN is needed for this. It's at least separate from CAP_MKNOD
328 * so we can give a container CAP_MKNOD to let it create devices but not
329 * modify the whitelist.
330 * It seems likely we'll want to add a CAP_CONTAINER capability to allow
331 * us to also grant CAP_SYS_ADMIN to containers without giving away the
332 * device whitelist controls, but for now we'll stick with CAP_SYS_ADMIN
333 *
334 * Taking rules away is always allowed (given CAP_SYS_ADMIN). Granting
335 * new access is only allowed if you're in the top-level cgroup, or your
336 * parent cgroup has the access you're asking for.
337 */
338static int devcgroup_update_access(struct dev_cgroup *devcgroup,
339                   int filetype, const char *buffer)
340{
341    const char *b;
342    char *endp;
343    int count;
344    struct dev_whitelist_item wh;
345
346    if (!capable(CAP_SYS_ADMIN))
347        return -EPERM;
348
349    memset(&wh, 0, sizeof(wh));
350    b = buffer;
351
352    switch (*b) {
353    case 'a':
354        wh.type = DEV_ALL;
355        wh.access = ACC_MASK;
356        wh.major = ~0;
357        wh.minor = ~0;
358        goto handle;
359    case 'b':
360        wh.type = DEV_BLOCK;
361        break;
362    case 'c':
363        wh.type = DEV_CHAR;
364        break;
365    default:
366        return -EINVAL;
367    }
368    b++;
369    if (!isspace(*b))
370        return -EINVAL;
371    b++;
372    if (*b == '*') {
373        wh.major = ~0;
374        b++;
375    } else if (isdigit(*b)) {
376        wh.major = simple_strtoul(b, &endp, 10);
377        b = endp;
378    } else {
379        return -EINVAL;
380    }
381    if (*b != ':')
382        return -EINVAL;
383    b++;
384
385    /* read minor */
386    if (*b == '*') {
387        wh.minor = ~0;
388        b++;
389    } else if (isdigit(*b)) {
390        wh.minor = simple_strtoul(b, &endp, 10);
391        b = endp;
392    } else {
393        return -EINVAL;
394    }
395    if (!isspace(*b))
396        return -EINVAL;
397    for (b++, count = 0; count < 3; count++, b++) {
398        switch (*b) {
399        case 'r':
400            wh.access |= ACC_READ;
401            break;
402        case 'w':
403            wh.access |= ACC_WRITE;
404            break;
405        case 'm':
406            wh.access |= ACC_MKNOD;
407            break;
408        case '\n':
409        case '\0':
410            count = 3;
411            break;
412        default:
413            return -EINVAL;
414        }
415    }
416
417handle:
418    switch (filetype) {
419    case DEVCG_ALLOW:
420        if (!parent_has_perm(devcgroup, &wh))
421            return -EPERM;
422        return dev_whitelist_add(devcgroup, &wh);
423    case DEVCG_DENY:
424        dev_whitelist_rm(devcgroup, &wh);
425        break;
426    default:
427        return -EINVAL;
428    }
429    return 0;
430}
431
432static int devcgroup_access_write(struct cgroup *cgrp, struct cftype *cft,
433                  const char *buffer)
434{
435    int retval;
436
437    mutex_lock(&devcgroup_mutex);
438    retval = devcgroup_update_access(cgroup_to_devcgroup(cgrp),
439                     cft->private, buffer);
440    mutex_unlock(&devcgroup_mutex);
441    return retval;
442}
443
444static struct cftype dev_cgroup_files[] = {
445    {
446        .name = "allow",
447        .write_string = devcgroup_access_write,
448        .private = DEVCG_ALLOW,
449    },
450    {
451        .name = "deny",
452        .write_string = devcgroup_access_write,
453        .private = DEVCG_DENY,
454    },
455    {
456        .name = "list",
457        .read_seq_string = devcgroup_seq_read,
458        .private = DEVCG_LIST,
459    },
460};
461
462static int devcgroup_populate(struct cgroup_subsys *ss,
463                struct cgroup *cgroup)
464{
465    return cgroup_add_files(cgroup, ss, dev_cgroup_files,
466                    ARRAY_SIZE(dev_cgroup_files));
467}
468
469struct cgroup_subsys devices_subsys = {
470    .name = "devices",
471    .can_attach = devcgroup_can_attach,
472    .create = devcgroup_create,
473    .destroy = devcgroup_destroy,
474    .populate = devcgroup_populate,
475    .subsys_id = devices_subsys_id,
476};
477
478int devcgroup_inode_permission(struct inode *inode, int mask)
479{
480    struct dev_cgroup *dev_cgroup;
481    struct dev_whitelist_item *wh;
482
483    dev_t device = inode->i_rdev;
484    if (!device)
485        return 0;
486    if (!S_ISBLK(inode->i_mode) && !S_ISCHR(inode->i_mode))
487        return 0;
488
489    rcu_read_lock();
490
491    dev_cgroup = task_devcgroup(current);
492
493    list_for_each_entry_rcu(wh, &dev_cgroup->whitelist, list) {
494        if (wh->type & DEV_ALL)
495            goto found;
496        if ((wh->type & DEV_BLOCK) && !S_ISBLK(inode->i_mode))
497            continue;
498        if ((wh->type & DEV_CHAR) && !S_ISCHR(inode->i_mode))
499            continue;
500        if (wh->major != ~0 && wh->major != imajor(inode))
501            continue;
502        if (wh->minor != ~0 && wh->minor != iminor(inode))
503            continue;
504
505        if ((mask & MAY_WRITE) && !(wh->access & ACC_WRITE))
506            continue;
507        if ((mask & MAY_READ) && !(wh->access & ACC_READ))
508            continue;
509found:
510        rcu_read_unlock();
511        return 0;
512    }
513
514    rcu_read_unlock();
515
516    return -EPERM;
517}
518
519int devcgroup_inode_mknod(int mode, dev_t dev)
520{
521    struct dev_cgroup *dev_cgroup;
522    struct dev_whitelist_item *wh;
523
524    if (!S_ISBLK(mode) && !S_ISCHR(mode))
525        return 0;
526
527    rcu_read_lock();
528
529    dev_cgroup = task_devcgroup(current);
530
531    list_for_each_entry_rcu(wh, &dev_cgroup->whitelist, list) {
532        if (wh->type & DEV_ALL)
533            goto found;
534        if ((wh->type & DEV_BLOCK) && !S_ISBLK(mode))
535            continue;
536        if ((wh->type & DEV_CHAR) && !S_ISCHR(mode))
537            continue;
538        if (wh->major != ~0 && wh->major != MAJOR(dev))
539            continue;
540        if (wh->minor != ~0 && wh->minor != MINOR(dev))
541            continue;
542
543        if (!(wh->access & ACC_MKNOD))
544            continue;
545found:
546        rcu_read_unlock();
547        return 0;
548    }
549
550    rcu_read_unlock();
551
552    return -EPERM;
553}
554

Archive Download this file



interactive