2 * dev_cgroup.c - device cgroup subsystem
4 * Copyright 2007 IBM Corp
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>
17 #define ACC_MASK (ACC_MKNOD | ACC_READ | ACC_WRITE)
21 #define DEV_ALL 4 /* this represents all devices */
24 * whitelist locking rules:
25 * cgroup_lock() cannot be taken under dev_cgroup->lock.
26 * dev_cgroup->lock can be taken with or without cgroup_lock().
28 * modifications always require cgroup_lock
29 * modifications to a list which is visible require the
30 * dev_cgroup->lock *and* cgroup_lock()
31 * walking the list requires dev_cgroup->lock or cgroup_lock().
33 * reasoning: dev_whitelist_copy() needs to kmalloc, so needs
34 * a mutex, which the cgroup_lock() is. Since modifying
35 * a visible list requires both locks, either lock can be
36 * taken for walking the list.
39 struct dev_whitelist_item {
43 struct list_head list;
47 struct cgroup_subsys_state css;
48 struct list_head whitelist;
52 static inline struct dev_cgroup *css_to_devcgroup(struct cgroup_subsys_state *s)
54 return container_of(s, struct dev_cgroup, css);
57 static inline struct dev_cgroup *cgroup_to_devcgroup(struct cgroup *cgroup)
59 return css_to_devcgroup(cgroup_subsys_state(cgroup, devices_subsys_id));
62 static inline struct dev_cgroup *task_devcgroup(struct task_struct *task)
64 return css_to_devcgroup(task_subsys_state(task, devices_subsys_id));
67 struct cgroup_subsys devices_subsys;
69 static int devcgroup_can_attach(struct cgroup_subsys *ss,
70 struct cgroup *new_cgroup, struct task_struct *task)
72 if (current != task && !capable(CAP_SYS_ADMIN))
79 * called under cgroup_lock()
81 static int dev_whitelist_copy(struct list_head *dest, struct list_head *orig)
83 struct dev_whitelist_item *wh, *tmp, *new;
85 list_for_each_entry(wh, orig, list) {
86 new = kmalloc(sizeof(*wh), GFP_KERNEL);
89 new->major = wh->major;
90 new->minor = wh->minor;
92 new->access = wh->access;
93 list_add_tail(&new->list, dest);
99 list_for_each_entry_safe(wh, tmp, dest, list) {
106 /* Stupid prototype - don't bother combining existing entries */
108 * called under cgroup_lock()
109 * since the list is visible to other tasks, we need the spinlock also
111 static int dev_whitelist_add(struct dev_cgroup *dev_cgroup,
112 struct dev_whitelist_item *wh)
114 struct dev_whitelist_item *whcopy, *walk;
116 whcopy = kmalloc(sizeof(*whcopy), GFP_KERNEL);
120 memcpy(whcopy, wh, sizeof(*whcopy));
121 spin_lock(&dev_cgroup->lock);
122 list_for_each_entry(walk, &dev_cgroup->whitelist, list) {
123 if (walk->type != wh->type)
125 if (walk->major != wh->major)
127 if (walk->minor != wh->minor)
130 walk->access |= wh->access;
136 list_add_tail(&whcopy->list, &dev_cgroup->whitelist);
137 spin_unlock(&dev_cgroup->lock);
142 * called under cgroup_lock()
143 * since the list is visible to other tasks, we need the spinlock also
145 static void dev_whitelist_rm(struct dev_cgroup *dev_cgroup,
146 struct dev_whitelist_item *wh)
148 struct dev_whitelist_item *walk, *tmp;
150 spin_lock(&dev_cgroup->lock);
151 list_for_each_entry_safe(walk, tmp, &dev_cgroup->whitelist, list) {
152 if (walk->type == DEV_ALL)
154 if (walk->type != wh->type)
156 if (walk->major != ~0 && walk->major != wh->major)
158 if (walk->minor != ~0 && walk->minor != wh->minor)
162 walk->access &= ~wh->access;
164 list_del(&walk->list);
168 spin_unlock(&dev_cgroup->lock);
172 * called from kernel/cgroup.c with cgroup_lock() held.
174 static struct cgroup_subsys_state *devcgroup_create(struct cgroup_subsys *ss,
175 struct cgroup *cgroup)
177 struct dev_cgroup *dev_cgroup, *parent_dev_cgroup;
178 struct cgroup *parent_cgroup;
181 dev_cgroup = kzalloc(sizeof(*dev_cgroup), GFP_KERNEL);
183 return ERR_PTR(-ENOMEM);
184 INIT_LIST_HEAD(&dev_cgroup->whitelist);
185 parent_cgroup = cgroup->parent;
187 if (parent_cgroup == NULL) {
188 struct dev_whitelist_item *wh;
189 wh = kmalloc(sizeof(*wh), GFP_KERNEL);
192 return ERR_PTR(-ENOMEM);
194 wh->minor = wh->major = ~0;
196 wh->access = ACC_MKNOD | ACC_READ | ACC_WRITE;
197 list_add(&wh->list, &dev_cgroup->whitelist);
199 parent_dev_cgroup = cgroup_to_devcgroup(parent_cgroup);
200 ret = dev_whitelist_copy(&dev_cgroup->whitelist,
201 &parent_dev_cgroup->whitelist);
208 spin_lock_init(&dev_cgroup->lock);
209 return &dev_cgroup->css;
212 static void devcgroup_destroy(struct cgroup_subsys *ss,
213 struct cgroup *cgroup)
215 struct dev_cgroup *dev_cgroup;
216 struct dev_whitelist_item *wh, *tmp;
218 dev_cgroup = cgroup_to_devcgroup(cgroup);
219 list_for_each_entry_safe(wh, tmp, &dev_cgroup->whitelist, list) {
226 #define DEVCG_ALLOW 1
233 static void set_access(char *acc, short access)
236 memset(acc, 0, ACCLEN);
237 if (access & ACC_READ)
239 if (access & ACC_WRITE)
241 if (access & ACC_MKNOD)
245 static char type_to_char(short type)
249 if (type == DEV_CHAR)
251 if (type == DEV_BLOCK)
256 static void set_majmin(char *str, unsigned m)
258 memset(str, 0, MAJMINLEN);
262 snprintf(str, MAJMINLEN, "%u", m);
265 static int devcgroup_seq_read(struct cgroup *cgroup, struct cftype *cft,
268 struct dev_cgroup *devcgroup = cgroup_to_devcgroup(cgroup);
269 struct dev_whitelist_item *wh;
270 char maj[MAJMINLEN], min[MAJMINLEN], acc[ACCLEN];
272 spin_lock(&devcgroup->lock);
273 list_for_each_entry(wh, &devcgroup->whitelist, list) {
274 set_access(acc, wh->access);
275 set_majmin(maj, wh->major);
276 set_majmin(min, wh->minor);
277 seq_printf(m, "%c %s:%s %s\n", type_to_char(wh->type),
280 spin_unlock(&devcgroup->lock);
286 * may_access_whitelist:
287 * does the access granted to dev_cgroup c contain the access
288 * requested in whitelist item refwh.
289 * return 1 if yes, 0 if no.
290 * call with c->lock held
292 static int may_access_whitelist(struct dev_cgroup *c,
293 struct dev_whitelist_item *refwh)
295 struct dev_whitelist_item *whitem;
297 list_for_each_entry(whitem, &c->whitelist, list) {
298 if (whitem->type & DEV_ALL)
300 if ((refwh->type & DEV_BLOCK) && !(whitem->type & DEV_BLOCK))
302 if ((refwh->type & DEV_CHAR) && !(whitem->type & DEV_CHAR))
304 if (whitem->major != ~0 && whitem->major != refwh->major)
306 if (whitem->minor != ~0 && whitem->minor != refwh->minor)
308 if (refwh->access & (~whitem->access))
317 * when adding a new allow rule to a device whitelist, the rule
318 * must be allowed in the parent device
320 static int parent_has_perm(struct dev_cgroup *childcg,
321 struct dev_whitelist_item *wh)
323 struct cgroup *pcg = childcg->css.cgroup->parent;
324 struct dev_cgroup *parent;
329 parent = cgroup_to_devcgroup(pcg);
330 spin_lock(&parent->lock);
331 ret = may_access_whitelist(parent, wh);
332 spin_unlock(&parent->lock);
337 * Modify the whitelist using allow/deny rules.
338 * CAP_SYS_ADMIN is needed for this. It's at least separate from CAP_MKNOD
339 * so we can give a container CAP_MKNOD to let it create devices but not
340 * modify the whitelist.
341 * It seems likely we'll want to add a CAP_CONTAINER capability to allow
342 * us to also grant CAP_SYS_ADMIN to containers without giving away the
343 * device whitelist controls, but for now we'll stick with CAP_SYS_ADMIN
345 * Taking rules away is always allowed (given CAP_SYS_ADMIN). Granting
346 * new access is only allowed if you're in the top-level cgroup, or your
347 * parent cgroup has the access you're asking for.
349 static int devcgroup_update_access(struct dev_cgroup *devcgroup,
350 int filetype, const char *buffer)
352 struct dev_cgroup *cur_devcgroup;
354 int retval = 0, count;
355 struct dev_whitelist_item wh;
357 if (!capable(CAP_SYS_ADMIN))
360 cur_devcgroup = task_devcgroup(current);
362 memset(&wh, 0, sizeof(wh));
368 wh.access = ACC_MASK;
388 } else if (isdigit(*b)) {
390 while (isdigit(*b)) {
391 wh.major = wh.major*10+(*b-'0');
405 } else if (isdigit(*b)) {
407 while (isdigit(*b)) {
408 wh.minor = wh.minor*10+(*b-'0');
416 for (b++, count = 0; count < 3; count++, b++) {
419 wh.access |= ACC_READ;
422 wh.access |= ACC_WRITE;
425 wh.access |= ACC_MKNOD;
440 if (!parent_has_perm(devcgroup, &wh))
442 return dev_whitelist_add(devcgroup, &wh);
444 dev_whitelist_rm(devcgroup, &wh);
452 static int devcgroup_access_write(struct cgroup *cgrp, struct cftype *cft,
456 if (!cgroup_lock_live_group(cgrp))
458 retval = devcgroup_update_access(cgroup_to_devcgroup(cgrp),
459 cft->private, buffer);
464 static struct cftype dev_cgroup_files[] = {
467 .write_string = devcgroup_access_write,
468 .private = DEVCG_ALLOW,
472 .write_string = devcgroup_access_write,
473 .private = DEVCG_DENY,
477 .read_seq_string = devcgroup_seq_read,
478 .private = DEVCG_LIST,
482 static int devcgroup_populate(struct cgroup_subsys *ss,
483 struct cgroup *cgroup)
485 return cgroup_add_files(cgroup, ss, dev_cgroup_files,
486 ARRAY_SIZE(dev_cgroup_files));
489 struct cgroup_subsys devices_subsys = {
491 .can_attach = devcgroup_can_attach,
492 .create = devcgroup_create,
493 .destroy = devcgroup_destroy,
494 .populate = devcgroup_populate,
495 .subsys_id = devices_subsys_id,
498 int devcgroup_inode_permission(struct inode *inode, int mask)
500 struct dev_cgroup *dev_cgroup;
501 struct dev_whitelist_item *wh;
503 dev_t device = inode->i_rdev;
506 if (!S_ISBLK(inode->i_mode) && !S_ISCHR(inode->i_mode))
508 dev_cgroup = css_to_devcgroup(task_subsys_state(current,
513 spin_lock(&dev_cgroup->lock);
514 list_for_each_entry(wh, &dev_cgroup->whitelist, list) {
515 if (wh->type & DEV_ALL)
517 if ((wh->type & DEV_BLOCK) && !S_ISBLK(inode->i_mode))
519 if ((wh->type & DEV_CHAR) && !S_ISCHR(inode->i_mode))
521 if (wh->major != ~0 && wh->major != imajor(inode))
523 if (wh->minor != ~0 && wh->minor != iminor(inode))
526 if ((mask & MAY_WRITE) && !(wh->access & ACC_WRITE))
528 if ((mask & MAY_READ) && !(wh->access & ACC_READ))
530 spin_unlock(&dev_cgroup->lock);
533 spin_unlock(&dev_cgroup->lock);
538 int devcgroup_inode_mknod(int mode, dev_t dev)
540 struct dev_cgroup *dev_cgroup;
541 struct dev_whitelist_item *wh;
543 dev_cgroup = css_to_devcgroup(task_subsys_state(current,
548 spin_lock(&dev_cgroup->lock);
549 list_for_each_entry(wh, &dev_cgroup->whitelist, list) {
550 if (wh->type & DEV_ALL)
552 if ((wh->type & DEV_BLOCK) && !S_ISBLK(mode))
554 if ((wh->type & DEV_CHAR) && !S_ISCHR(mode))
556 if (wh->major != ~0 && wh->major != MAJOR(dev))
558 if (wh->minor != ~0 && wh->minor != MINOR(dev))
561 if (!(wh->access & ACC_MKNOD))
563 spin_unlock(&dev_cgroup->lock);
566 spin_unlock(&dev_cgroup->lock);