security/device_cgroup.c

   1 /*
   2  * dev_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
  14 #define ACC_MKNOD 1
  15 #define ACC_READ  2
  16 #define ACC_WRITE 4
  17 #define ACC_MASK (ACC_MKNOD | ACC_READ | ACC_WRITE)
  18
  19 #define DEV_BLOCK 1
  20 #define DEV_CHAR  2
  21 #define DEV_ALL   4  /* this represents all devices */
  22
  23 /*
  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().
  27  *
  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().
  32  *
  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.
  37  */
  38
  39 struct dev_whitelist_item {
  40         u32 major, minor;
  41         short type;
  42         short access;
  43         struct list_head list;
  44         struct rcu_head rcu;
  45 };
  46
  47 struct dev_cgroup {
  48         struct cgroup_subsys_state css;
  49         struct list_head whitelist;
  50         spinlock_t lock;
  51 };
  52
  53 static inline struct dev_cgroup *css_to_devcgroup(struct cgroup_subsys_state *s)
  54 {
  55         return container_of(s, struct dev_cgroup, css);
  56 }
  57
  58 static inline struct dev_cgroup *cgroup_to_devcgroup(struct cgroup *cgroup)
  59 {
  60         return css_to_devcgroup(cgroup_subsys_state(cgroup, devices_subsys_id));
  61 }
  62
  63 static inline struct dev_cgroup *task_devcgroup(struct task_struct *task)
  64 {
  65         return css_to_devcgroup(task_subsys_state(task, devices_subsys_id));
  66 }
  67
  68 struct cgroup_subsys devices_subsys;
  69
  70 static int devcgroup_can_attach(struct cgroup_subsys *ss,
  71                 struct cgroup *new_cgroup, struct task_struct *task)
  72 {
  73         if (current != task && !capable(CAP_SYS_ADMIN))
  74                         return -EPERM;
  75
  76         return 0;
  77 }
  78
  79 /*
  80  * called under cgroup_lock()
  81  */
  82 static int dev_whitelist_copy(struct list_head *dest, struct list_head *orig)
  83 {
  84         struct dev_whitelist_item *wh, *tmp, *new;
  85
  86         list_for_each_entry(wh, orig, list) {
  87                 new = kmalloc(sizeof(*wh), GFP_KERNEL);
  88                 if (!new)
  89                         goto free_and_exit;
  90                 new->major = wh->major;
  91                 new->minor = wh->minor;
  92                 new->type = wh->type;
  93                 new->access = wh->access;
  94                 list_add_tail(&new->list, dest);
  95         }
  96
  97         return 0;
  98
  99 free_and_exit:
 100         list_for_each_entry_safe(wh, tmp, dest, list) {
 101                 list_del(&wh->list);
 102                 kfree(wh);
 103         }
 104         return -ENOMEM;
 105 }
 106
 107 /* Stupid prototype - don't bother combining existing entries */
 108 /*
 109  * called under cgroup_lock()
 110  * since the list is visible to other tasks, we need the spinlock also
 111  */
 112 static int dev_whitelist_add(struct dev_cgroup *dev_cgroup,
 113                         struct dev_whitelist_item *wh)
 114 {
 115         struct dev_whitelist_item *whcopy, *walk;
 116
 117         whcopy = kmalloc(sizeof(*whcopy), GFP_KERNEL);
 118         if (!whcopy)
 119                 return -ENOMEM;
 120
 121         memcpy(whcopy, wh, sizeof(*whcopy));
 122         spin_lock(&dev_cgroup->lock);
 123         list_for_each_entry(walk, &dev_cgroup->whitelist, list) {
 124                 if (walk->type != wh->type)
 125                         continue;
 126                 if (walk->major != wh->major)
 127                         continue;
 128                 if (walk->minor != wh->minor)
 129                         continue;
 130
 131                 walk->access |= wh->access;
 132                 kfree(whcopy);
 133                 whcopy = NULL;
 134         }
 135
 136         if (whcopy != NULL)
 137                 list_add_tail_rcu(&whcopy->list, &dev_cgroup->whitelist);
 138         spin_unlock(&dev_cgroup->lock);
 139         return 0;
 140 }
 141
 142 static void whitelist_item_free(struct rcu_head *rcu)
 143 {
 144         struct dev_whitelist_item *item;
 145
 146         item = container_of(rcu, struct dev_whitelist_item, rcu);
 147         kfree(item);
 148 }
 149
 150 /*
 151  * called under cgroup_lock()
 152  * since the list is visible to other tasks, we need the spinlock also
 153  */
 154 static void dev_whitelist_rm(struct dev_cgroup *dev_cgroup,
 155                         struct dev_whitelist_item *wh)
 156 {
 157         struct dev_whitelist_item *walk, *tmp;
 158
 159         spin_lock(&dev_cgroup->lock);
 160         list_for_each_entry_safe(walk, tmp, &dev_cgroup->whitelist, list) {
 161                 if (walk->type == DEV_ALL)
 162                         goto remove;
 163                 if (walk->type != wh->type)
 164                         continue;
 165                 if (walk->major != ~0 && walk->major != wh->major)
 166                         continue;
 167                 if (walk->minor != ~0 && walk->minor != wh->minor)
 168                         continue;
 169
 170 remove:
 171                 walk->access &= ~wh->access;
 172                 if (!walk->access) {
 173                         list_del_rcu(&walk->list);
 174                         call_rcu(&walk->rcu, whitelist_item_free);
 175                 }
 176         }
 177         spin_unlock(&dev_cgroup->lock);
 178 }
 179
 180 /*
 181  * called from kernel/cgroup.c with cgroup_lock() held.
 182  */
 183 static struct cgroup_subsys_state *devcgroup_create(struct cgroup_subsys *ss,
 184                                                 struct cgroup *cgroup)
 185 {
 186         struct dev_cgroup *dev_cgroup, *parent_dev_cgroup;
 187         struct cgroup *parent_cgroup;
 188         int ret;
 189
 190         dev_cgroup = kzalloc(sizeof(*dev_cgroup), GFP_KERNEL);
 191         if (!dev_cgroup)
 192                 return ERR_PTR(-ENOMEM);
 193         INIT_LIST_HEAD(&dev_cgroup->whitelist);
 194         parent_cgroup = cgroup->parent;
 195
 196         if (parent_cgroup == NULL) {
 197                 struct dev_whitelist_item *wh;
 198                 wh = kmalloc(sizeof(*wh), GFP_KERNEL);
 199                 if (!wh) {
 200                         kfree(dev_cgroup);
 201                         return ERR_PTR(-ENOMEM);
 202                 }
 203                 wh->minor = wh->major = ~0;
 204                 wh->type = DEV_ALL;
 205                 wh->access = ACC_MASK;
 206                 list_add(&wh->list, &dev_cgroup->whitelist);
 207         } else {
 208                 parent_dev_cgroup = cgroup_to_devcgroup(parent_cgroup);
 209                 ret = dev_whitelist_copy(&dev_cgroup->whitelist,
 210                                 &parent_dev_cgroup->whitelist);
 211                 if (ret) {
 212                         kfree(dev_cgroup);
 213                         return ERR_PTR(ret);
 214                 }
 215         }
 216
 217         spin_lock_init(&dev_cgroup->lock);
 218         return &dev_cgroup->css;
 219 }
 220
 221 static void devcgroup_destroy(struct cgroup_subsys *ss,
 222                         struct cgroup *cgroup)
 223 {
 224         struct dev_cgroup *dev_cgroup;
 225         struct dev_whitelist_item *wh, *tmp;
 226
 227         dev_cgroup = cgroup_to_devcgroup(cgroup);
 228         list_for_each_entry_safe(wh, tmp, &dev_cgroup->whitelist, list) {
 229                 list_del(&wh->list);
 230                 kfree(wh);
 231         }
 232         kfree(dev_cgroup);
 233 }
 234
 235 #define DEVCG_ALLOW 1
 236 #define DEVCG_DENY 2
 237 #define DEVCG_LIST 3
 238
 239 #define MAJMINLEN 13
 240 #define ACCLEN 4
 241
 242 static void set_access(char *acc, short access)
 243 {
 244         int idx = 0;
 245         memset(acc, 0, ACCLEN);
 246         if (access & ACC_READ)
 247                 acc[idx++] = 'r';
 248         if (access & ACC_WRITE)
 249                 acc[idx++] = 'w';
 250         if (access & ACC_MKNOD)
 251                 acc[idx++] = 'm';
 252 }
 253
 254 static char type_to_char(short type)
 255 {
 256         if (type == DEV_ALL)
 257                 return 'a';
 258         if (type == DEV_CHAR)
 259                 return 'c';
 260         if (type == DEV_BLOCK)
 261                 return 'b';
 262         return 'X';
 263 }
 264
 265 static void set_majmin(char *str, unsigned m)
 266 {
 267         if (m == ~0)
 268                 strcpy(str, "*");
 269         else
 270                 sprintf(str, "%u", m);
 271 }
 272
 273 static int devcgroup_seq_read(struct cgroup *cgroup, struct cftype *cft,
 274                                 struct seq_file *m)
 275 {
 276         struct dev_cgroup *devcgroup = cgroup_to_devcgroup(cgroup);
 277         struct dev_whitelist_item *wh;
 278         char maj[MAJMINLEN], min[MAJMINLEN], acc[ACCLEN];
 279
 280         rcu_read_lock();
 281         list_for_each_entry_rcu(wh, &devcgroup->whitelist, list) {
 282                 set_access(acc, wh->access);
 283                 set_majmin(maj, wh->major);
 284                 set_majmin(min, wh->minor);
 285                 seq_printf(m, "%c %s:%s %s\n", type_to_char(wh->type),
 286                            maj, min, acc);
 287         }
 288         rcu_read_unlock();
 289
 290         return 0;
 291 }
 292
 293 /*
 294  * may_access_whitelist:
 295  * does the access granted to dev_cgroup c contain the access
 296  * requested in whitelist item refwh.
 297  * return 1 if yes, 0 if no.
 298  * call with c->lock held
 299  */
 300 static int may_access_whitelist(struct dev_cgroup *c,
 301                                        struct dev_whitelist_item *refwh)
 302 {
 303         struct dev_whitelist_item *whitem;
 304
 305         list_for_each_entry(whitem, &c->whitelist, list) {
 306                 if (whitem->type & DEV_ALL)
 307                         return 1;
 308                 if ((refwh->type & DEV_BLOCK) && !(whitem->type & DEV_BLOCK))
 309                         continue;
 310                 if ((refwh->type & DEV_CHAR) && !(whitem->type & DEV_CHAR))
 311                         continue;
 312                 if (whitem->major != ~0 && whitem->major != refwh->major)
 313                         continue;
 314                 if (whitem->minor != ~0 && whitem->minor != refwh->minor)
 315                         continue;
 316                 if (refwh->access & (~whitem->access))
 317                         continue;
 318                 return 1;
 319         }
 320         return 0;
 321 }
 322
 323 /*
 324  * parent_has_perm:
 325  * when adding a new allow rule to a device whitelist, the rule
 326  * must be allowed in the parent device
 327  */
 328 static int parent_has_perm(struct dev_cgroup *childcg,
 329                                   struct dev_whitelist_item *wh)
 330 {
 331         struct cgroup *pcg = childcg->css.cgroup->parent;
 332         struct dev_cgroup *parent;
 333         int ret;
 334
 335         if (!pcg)
 336                 return 1;
 337         parent = cgroup_to_devcgroup(pcg);
 338         spin_lock(&parent->lock);
 339         ret = may_access_whitelist(parent, wh);
 340         spin_unlock(&parent->lock);
 341         return ret;
 342 }
 343
 344 /*
 345  * Modify the whitelist using allow/deny rules.
 346  * CAP_SYS_ADMIN is needed for this.  It's at least separate from CAP_MKNOD
 347  * so we can give a container CAP_MKNOD to let it create devices but not
 348  * modify the whitelist.
 349  * It seems likely we'll want to add a CAP_CONTAINER capability to allow
 350  * us to also grant CAP_SYS_ADMIN to containers without giving away the
 351  * device whitelist controls, but for now we'll stick with CAP_SYS_ADMIN
 352  *
 353  * Taking rules away is always allowed (given CAP_SYS_ADMIN).  Granting
 354  * new access is only allowed if you're in the top-level cgroup, or your
 355  * parent cgroup has the access you're asking for.
 356  */
 357 static int devcgroup_update_access(struct dev_cgroup *devcgroup,
 358                                    int filetype, const char *buffer)
 359 {
 360         struct dev_cgroup *cur_devcgroup;
 361         const char *b;
 362         char *endp;
 363         int retval = 0, count;
 364         struct dev_whitelist_item wh;
 365
 366         if (!capable(CAP_SYS_ADMIN))
 367                 return -EPERM;
 368
 369         cur_devcgroup = task_devcgroup(current);
 370
 371         memset(&wh, 0, sizeof(wh));
 372         b = buffer;
 373
 374         switch (*b) {
 375         case 'a':
 376                 wh.type = DEV_ALL;
 377                 wh.access = ACC_MASK;
 378                 wh.major = ~0;
 379                 wh.minor = ~0;
 380                 goto handle;
 381         case 'b':
 382                 wh.type = DEV_BLOCK;
 383                 break;
 384         case 'c':
 385                 wh.type = DEV_CHAR;
 386                 break;
 387         default:
 388                 return -EINVAL;
 389         }
 390         b++;
 391         if (!isspace(*b))
 392                 return -EINVAL;
 393         b++;
 394         if (*b == '*') {
 395                 wh.major = ~0;
 396                 b++;
 397         } else if (isdigit(*b)) {
 398                 wh.major = simple_strtoul(b, &endp, 10);
 399                 b = endp;
 400         } else {
 401                 return -EINVAL;
 402         }
 403         if (*b != ':')
 404                 return -EINVAL;
 405         b++;
 406
 407         /* read minor */
 408         if (*b == '*') {
 409                 wh.minor = ~0;
 410                 b++;
 411         } else if (isdigit(*b)) {
 412                 wh.minor = simple_strtoul(b, &endp, 10);
 413                 b = endp;
 414         } else {
 415                 return -EINVAL;
 416         }
 417         if (!isspace(*b))
 418                 return -EINVAL;
 419         for (b++, count = 0; count < 3; count++, b++) {
 420                 switch (*b) {
 421                 case 'r':
 422                         wh.access |= ACC_READ;
 423                         break;
 424                 case 'w':
 425                         wh.access |= ACC_WRITE;
 426                         break;
 427                 case 'm':
 428                         wh.access |= ACC_MKNOD;
 429                         break;
 430                 case '\n':
 431                 case '\0':
 432                         count = 3;
 433                         break;
 434                 default:
 435                         return -EINVAL;
 436                 }
 437         }
 438
 439 handle:
 440         retval = 0;
 441         switch (filetype) {
 442         case DEVCG_ALLOW:
 443                 if (!parent_has_perm(devcgroup, &wh))
 444                         return -EPERM;
 445                 return dev_whitelist_add(devcgroup, &wh);
 446         case DEVCG_DENY:
 447                 dev_whitelist_rm(devcgroup, &wh);
 448                 break;
 449         default:
 450                 return -EINVAL;
 451         }
 452         return 0;
 453 }
 454
 455 static int devcgroup_access_write(struct cgroup *cgrp, struct cftype *cft,
 456                                   const char *buffer)
 457 {
 458         int retval;
 459         if (!cgroup_lock_live_group(cgrp))
 460                 return -ENODEV;
 461         retval = devcgroup_update_access(cgroup_to_devcgroup(cgrp),
 462                                          cft->private, buffer);
 463         cgroup_unlock();
 464         return retval;
 465 }
 466
 467 static struct cftype dev_cgroup_files[] = {
 468         {
 469                 .name = "allow",
 470                 .write_string  = devcgroup_access_write,
 471                 .private = DEVCG_ALLOW,
 472         },
 473         {
 474                 .name = "deny",
 475                 .write_string = devcgroup_access_write,
 476                 .private = DEVCG_DENY,
 477         },
 478         {
 479                 .name = "list",
 480                 .read_seq_string = devcgroup_seq_read,
 481                 .private = DEVCG_LIST,
 482         },
 483 };
 484
 485 static int devcgroup_populate(struct cgroup_subsys *ss,
 486                                 struct cgroup *cgroup)
 487 {
 488         return cgroup_add_files(cgroup, ss, dev_cgroup_files,
 489                                         ARRAY_SIZE(dev_cgroup_files));
 490 }
 491
 492 struct cgroup_subsys devices_subsys = {
 493         .name = "devices",
 494         .can_attach = devcgroup_can_attach,
 495         .create = devcgroup_create,
 496         .destroy  = devcgroup_destroy,
 497         .populate = devcgroup_populate,
 498         .subsys_id = devices_subsys_id,
 499 };
 500
 501 int devcgroup_inode_permission(struct inode *inode, int mask)
 502 {
 503         struct dev_cgroup *dev_cgroup;
 504         struct dev_whitelist_item *wh;
 505
 506         dev_t device = inode->i_rdev;
 507         if (!device)
 508                 return 0;
 509         if (!S_ISBLK(inode->i_mode) && !S_ISCHR(inode->i_mode))
 510                 return 0;
 511
 512         rcu_read_lock();
 513
 514         dev_cgroup = task_devcgroup(current);
 515
 516         list_for_each_entry_rcu(wh, &dev_cgroup->whitelist, list) {
 517                 if (wh->type & DEV_ALL)
 518                         goto acc_check;
 519                 if ((wh->type & DEV_BLOCK) && !S_ISBLK(inode->i_mode))
 520                         continue;
 521                 if ((wh->type & DEV_CHAR) && !S_ISCHR(inode->i_mode))
 522                         continue;
 523                 if (wh->major != ~0 && wh->major != imajor(inode))
 524                         continue;
 525                 if (wh->minor != ~0 && wh->minor != iminor(inode))
 526                         continue;
 527 acc_check:
 528                 if ((mask & MAY_WRITE) && !(wh->access & ACC_WRITE))
 529                         continue;
 530                 if ((mask & MAY_READ) && !(wh->access & ACC_READ))
 531                         continue;
 532                 rcu_read_unlock();
 533                 return 0;
 534         }
 535
 536         rcu_read_unlock();
 537
 538         return -EPERM;
 539 }
 540
 541 int devcgroup_inode_mknod(int mode, dev_t dev)
 542 {
 543         struct dev_cgroup *dev_cgroup;
 544         struct dev_whitelist_item *wh;
 545
 546         rcu_read_lock();
 547
 548         dev_cgroup = task_devcgroup(current);
 549
 550         list_for_each_entry(wh, &dev_cgroup->whitelist, list) {
 551                 if (wh->type & DEV_ALL)
 552                         goto acc_check;
 553                 if ((wh->type & DEV_BLOCK) && !S_ISBLK(mode))
 554                         continue;
 555                 if ((wh->type & DEV_CHAR) && !S_ISCHR(mode))
 556                         continue;
 557                 if (wh->major != ~0 && wh->major != MAJOR(dev))
 558                         continue;
 559                 if (wh->minor != ~0 && wh->minor != MINOR(dev))
 560                         continue;
 561 acc_check:
 562                 if (!(wh->access & ACC_MKNOD))
 563                         continue;
 564                 rcu_read_unlock();
 565                 return 0;
 566         }
 567
 568         rcu_read_unlock();
 569
 570         return -EPERM;
 571 }