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/rcupdate.h>
  14 #include <linux/mutex.h>
  15
  16 #define ACC_MKNOD 1
  17 #define ACC_READ  2
  18 #define ACC_WRITE 4
  19 #define ACC_MASK (ACC_MKNOD | ACC_READ | ACC_WRITE)
  20
  21 #define DEV_BLOCK 1
  22 #define DEV_CHAR  2
  23 #define DEV_ALL   4  /* this represents all devices */
  24
  25 static DEFINE_MUTEX(devcgroup_mutex);
  26
  27 /*
  28  * whitelist locking rules:
  29  * hold devcgroup_mutex for update/read.
  30  * hold rcu_read_lock() for read.
  31  */
  32
  33 struct dev_whitelist_item {
  34         u32 major, minor;
  35         short type;
  36         short access;
  37         struct list_head list;
  38         struct rcu_head rcu;
  39 };
  40
  41 struct dev_cgroup {
  42         struct cgroup_subsys_state css;
  43         struct list_head whitelist;
  44 };
  45
  46 static inline struct dev_cgroup *css_to_devcgroup(struct cgroup_subsys_state *s)
  47 {
  48         return container_of(s, struct dev_cgroup, css);
  49 }
  50
  51 static inline struct dev_cgroup *cgroup_to_devcgroup(struct cgroup *cgroup)
  52 {
  53         return css_to_devcgroup(cgroup_subsys_state(cgroup, devices_subsys_id));
  54 }
  55
  56 static inline struct dev_cgroup *task_devcgroup(struct task_struct *task)
  57 {
  58         return css_to_devcgroup(task_subsys_state(task, devices_subsys_id));
  59 }
  60
  61 struct cgroup_subsys devices_subsys;
  62
  63 static int devcgroup_can_attach(struct cgroup_subsys *ss,
  64                 struct cgroup *new_cgroup, struct task_struct *task)
  65 {
  66         if (current != task && !capable(CAP_SYS_ADMIN))
  67                         return -EPERM;
  68
  69         return 0;
  70 }
  71
  72 /*
  73  * called under devcgroup_mutex
  74  */
  75 static int dev_whitelist_copy(struct list_head *dest, struct list_head *orig)
  76 {
  77         struct dev_whitelist_item *wh, *tmp, *new;
  78
  79         list_for_each_entry(wh, orig, list) {
  80                 new = kmemdup(wh, sizeof(*wh), GFP_KERNEL);
  81                 if (!new)
  82                         goto free_and_exit;
  83                 list_add_tail(&new->list, dest);
  84         }
  85
  86         return 0;
  87
  88 free_and_exit:
  89         list_for_each_entry_safe(wh, tmp, dest, list) {
  90                 list_del(&wh->list);
  91                 kfree(wh);
  92         }
  93         return -ENOMEM;
  94 }
  95
  96 /* Stupid prototype - don't bother combining existing entries */
  97 /*
  98  * called under devcgroup_mutex
  99  */
 100 static int dev_whitelist_add(struct dev_cgroup *dev_cgroup,
 101                         struct dev_whitelist_item *wh)
 102 {
 103         struct dev_whitelist_item *whcopy, *walk;
 104
 105         whcopy = kmemdup(wh, sizeof(*wh), GFP_KERNEL);
 106         if (!whcopy)
 107                 return -ENOMEM;
 108
 109         list_for_each_entry(walk, &dev_cgroup->whitelist, list) {
 110                 if (walk->type != wh->type)
 111                         continue;
 112                 if (walk->major != wh->major)
 113                         continue;
 114                 if (walk->minor != wh->minor)
 115                         continue;
 116
 117                 walk->access |= wh->access;
 118                 kfree(whcopy);
 119                 whcopy = NULL;
 120         }
 121
 122         if (whcopy != NULL)
 123                 list_add_tail_rcu(&whcopy->list, &dev_cgroup->whitelist);
 124         return 0;
 125 }
 126
 127 static void whitelist_item_free(struct rcu_head *rcu)
 128 {
 129         struct dev_whitelist_item *item;
 130
 131         item = container_of(rcu, struct dev_whitelist_item, rcu);
 132         kfree(item);
 133 }
 134
 135 /*
 136  * called under devcgroup_mutex
 137  */
 138 static void dev_whitelist_rm(struct dev_cgroup *dev_cgroup,
 139                         struct dev_whitelist_item *wh)
 140 {
 141         struct dev_whitelist_item *walk, *tmp;
 142
 143         list_for_each_entry_safe(walk, tmp, &dev_cgroup->whitelist, list) {
 144                 if (walk->type == DEV_ALL)
 145                         goto remove;
 146                 if (walk->type != wh->type)
 147                         continue;
 148                 if (walk->major != ~0 && walk->major != wh->major)
 149                         continue;
 150                 if (walk->minor != ~0 && walk->minor != wh->minor)
 151                         continue;
 152
 153 remove:
 154                 walk->access &= ~wh->access;
 155                 if (!walk->access) {
 156                         list_del_rcu(&walk->list);
 157                         call_rcu(&walk->rcu, whitelist_item_free);
 158                 }
 159         }
 160 }
 161
 162 /*
 163  * called from kernel/cgroup.c with cgroup_lock() held.
 164  */
 165 static struct cgroup_subsys_state *devcgroup_create(struct cgroup_subsys *ss,
 166                                                 struct cgroup *cgroup)
 167 {
 168         struct dev_cgroup *dev_cgroup, *parent_dev_cgroup;
 169         struct cgroup *parent_cgroup;
 170         int ret;
 171
 172         dev_cgroup = kzalloc(sizeof(*dev_cgroup), GFP_KERNEL);
 173         if (!dev_cgroup)
 174                 return ERR_PTR(-ENOMEM);
 175         INIT_LIST_HEAD(&dev_cgroup->whitelist);
 176         parent_cgroup = cgroup->parent;
 177
 178         if (parent_cgroup == NULL) {
 179                 struct dev_whitelist_item *wh;
 180                 wh = kmalloc(sizeof(*wh), GFP_KERNEL);
 181                 if (!wh) {
 182                         kfree(dev_cgroup);
 183                         return ERR_PTR(-ENOMEM);
 184                 }
 185                 wh->minor = wh->major = ~0;
 186                 wh->type = DEV_ALL;
 187                 wh->access = ACC_MASK;
 188                 list_add(&wh->list, &dev_cgroup->whitelist);
 189         } else {
 190                 parent_dev_cgroup = cgroup_to_devcgroup(parent_cgroup);
 191                 mutex_lock(&devcgroup_mutex);
 192                 ret = dev_whitelist_copy(&dev_cgroup->whitelist,
 193                                 &parent_dev_cgroup->whitelist);
 194                 mutex_unlock(&devcgroup_mutex);
 195                 if (ret) {
 196                         kfree(dev_cgroup);
 197                         return ERR_PTR(ret);
 198                 }
 199         }
 200
 201         return &dev_cgroup->css;
 202 }
 203
 204 static void devcgroup_destroy(struct cgroup_subsys *ss,
 205                         struct cgroup *cgroup)
 206 {
 207         struct dev_cgroup *dev_cgroup;
 208         struct dev_whitelist_item *wh, *tmp;
 209
 210         dev_cgroup = cgroup_to_devcgroup(cgroup);
 211         list_for_each_entry_safe(wh, tmp, &dev_cgroup->whitelist, list) {
 212                 list_del(&wh->list);
 213                 kfree(wh);
 214         }
 215         kfree(dev_cgroup);
 216 }
 217
 218 #define DEVCG_ALLOW 1
 219 #define DEVCG_DENY 2
 220 #define DEVCG_LIST 3
 221
 222 #define MAJMINLEN 13
 223 #define ACCLEN 4
 224
 225 static void set_access(char *acc, short access)
 226 {
 227         int idx = 0;
 228         memset(acc, 0, ACCLEN);
 229         if (access & ACC_READ)
 230                 acc[idx++] = 'r';
 231         if (access & ACC_WRITE)
 232                 acc[idx++] = 'w';
 233         if (access & ACC_MKNOD)
 234                 acc[idx++] = 'm';
 235 }
 236
 237 static char type_to_char(short type)
 238 {
 239         if (type == DEV_ALL)
 240                 return 'a';
 241         if (type == DEV_CHAR)
 242                 return 'c';
 243         if (type == DEV_BLOCK)
 244                 return 'b';
 245         return 'X';
 246 }
 247
 248 static void set_majmin(char *str, unsigned m)
 249 {
 250         if (m == ~0)
 251                 strcpy(str, "*");
 252         else
 253                 sprintf(str, "%u", m);
 254 }
 255
 256 static int devcgroup_seq_read(struct cgroup *cgroup, struct cftype *cft,
 257                                 struct seq_file *m)
 258 {
 259         struct dev_cgroup *devcgroup = cgroup_to_devcgroup(cgroup);
 260         struct dev_whitelist_item *wh;
 261         char maj[MAJMINLEN], min[MAJMINLEN], acc[ACCLEN];
 262
 263         rcu_read_lock();
 264         list_for_each_entry_rcu(wh, &devcgroup->whitelist, list) {
 265                 set_access(acc, wh->access);
 266                 set_majmin(maj, wh->major);
 267                 set_majmin(min, wh->minor);
 268                 seq_printf(m, "%c %s:%s %s\n", type_to_char(wh->type),
 269                            maj, min, acc);
 270         }
 271         rcu_read_unlock();
 272
 273         return 0;
 274 }
 275
 276 /*
 277  * may_access_whitelist:
 278  * does the access granted to dev_cgroup c contain the access
 279  * requested in whitelist item refwh.
 280  * return 1 if yes, 0 if no.
 281  * call with devcgroup_mutex held
 282  */
 283 static int may_access_whitelist(struct dev_cgroup *c,
 284                                        struct dev_whitelist_item *refwh)
 285 {
 286         struct dev_whitelist_item *whitem;
 287
 288         list_for_each_entry(whitem, &c->whitelist, list) {
 289                 if (whitem->type & DEV_ALL)
 290                         return 1;
 291                 if ((refwh->type & DEV_BLOCK) && !(whitem->type & DEV_BLOCK))
 292                         continue;
 293                 if ((refwh->type & DEV_CHAR) && !(whitem->type & DEV_CHAR))
 294                         continue;
 295                 if (whitem->major != ~0 && whitem->major != refwh->major)
 296                         continue;
 297                 if (whitem->minor != ~0 && whitem->minor != refwh->minor)
 298                         continue;
 299                 if (refwh->access & (~whitem->access))
 300                         continue;
 301                 return 1;
 302         }
 303         return 0;
 304 }
 305
 306 /*
 307  * parent_has_perm:
 308  * when adding a new allow rule to a device whitelist, the rule
 309  * must be allowed in the parent device
 310  */
 311 static int parent_has_perm(struct dev_cgroup *childcg,
 312                                   struct dev_whitelist_item *wh)
 313 {
 314         struct cgroup *pcg = childcg->css.cgroup->parent;
 315         struct dev_cgroup *parent;
 316
 317         if (!pcg)
 318                 return 1;
 319         parent = cgroup_to_devcgroup(pcg);
 320         return may_access_whitelist(parent, wh);
 321 }
 322
 323 /*
 324  * Modify the whitelist using allow/deny rules.
 325  * CAP_SYS_ADMIN is needed for this.  It's at least separate from CAP_MKNOD
 326  * so we can give a container CAP_MKNOD to let it create devices but not
 327  * modify the whitelist.
 328  * It seems likely we'll want to add a CAP_CONTAINER capability to allow
 329  * us to also grant CAP_SYS_ADMIN to containers without giving away the
 330  * device whitelist controls, but for now we'll stick with CAP_SYS_ADMIN
 331  *
 332  * Taking rules away is always allowed (given CAP_SYS_ADMIN).  Granting
 333  * new access is only allowed if you're in the top-level cgroup, or your
 334  * parent cgroup has the access you're asking for.
 335  */
 336 static int devcgroup_update_access(struct dev_cgroup *devcgroup,
 337                                    int filetype, const char *buffer)
 338 {
 339         const char *b;
 340         char *endp;
 341         int count;
 342         struct dev_whitelist_item wh;
 343
 344         if (!capable(CAP_SYS_ADMIN))
 345                 return -EPERM;
 346
 347         memset(&wh, 0, sizeof(wh));
 348         b = buffer;
 349
 350         switch (*b) {
 351         case 'a':
 352                 wh.type = DEV_ALL;
 353                 wh.access = ACC_MASK;
 354                 wh.major = ~0;
 355                 wh.minor = ~0;
 356                 goto handle;
 357         case 'b':
 358                 wh.type = DEV_BLOCK;
 359                 break;
 360         case 'c':
 361                 wh.type = DEV_CHAR;
 362                 break;
 363         default:
 364                 return -EINVAL;
 365         }
 366         b++;
 367         if (!isspace(*b))
 368                 return -EINVAL;
 369         b++;
 370         if (*b == '*') {
 371                 wh.major = ~0;
 372                 b++;
 373         } else if (isdigit(*b)) {
 374                 wh.major = simple_strtoul(b, &endp, 10);
 375                 b = endp;
 376         } else {
 377                 return -EINVAL;
 378         }
 379         if (*b != ':')
 380                 return -EINVAL;
 381         b++;
 382
 383         /* read minor */
 384         if (*b == '*') {
 385                 wh.minor = ~0;
 386                 b++;
 387         } else if (isdigit(*b)) {
 388                 wh.minor = simple_strtoul(b, &endp, 10);
 389                 b = endp;
 390         } else {
 391                 return -EINVAL;
 392         }
 393         if (!isspace(*b))
 394                 return -EINVAL;
 395         for (b++, count = 0; count < 3; count++, b++) {
 396                 switch (*b) {
 397                 case 'r':
 398                         wh.access |= ACC_READ;
 399                         break;
 400                 case 'w':
 401                         wh.access |= ACC_WRITE;
 402                         break;
 403                 case 'm':
 404                         wh.access |= ACC_MKNOD;
 405                         break;
 406                 case '\n':
 407                 case '\0':
 408                         count = 3;
 409                         break;
 410                 default:
 411                         return -EINVAL;
 412                 }
 413         }
 414
 415 handle:
 416         switch (filetype) {
 417         case DEVCG_ALLOW:
 418                 if (!parent_has_perm(devcgroup, &wh))
 419                         return -EPERM;
 420                 return dev_whitelist_add(devcgroup, &wh);
 421         case DEVCG_DENY:
 422                 dev_whitelist_rm(devcgroup, &wh);
 423                 break;
 424         default:
 425                 return -EINVAL;
 426         }
 427         return 0;
 428 }
 429
 430 static int devcgroup_access_write(struct cgroup *cgrp, struct cftype *cft,
 431                                   const char *buffer)
 432 {
 433         int retval;
 434
 435         mutex_lock(&devcgroup_mutex);
 436         retval = devcgroup_update_access(cgroup_to_devcgroup(cgrp),
 437                                          cft->private, buffer);
 438         mutex_unlock(&devcgroup_mutex);
 439         return retval;
 440 }
 441
 442 static struct cftype dev_cgroup_files[] = {
 443         {
 444                 .name = "allow",
 445                 .write_string  = devcgroup_access_write,
 446                 .private = DEVCG_ALLOW,
 447         },
 448         {
 449                 .name = "deny",
 450                 .write_string = devcgroup_access_write,
 451                 .private = DEVCG_DENY,
 452         },
 453         {
 454                 .name = "list",
 455                 .read_seq_string = devcgroup_seq_read,
 456                 .private = DEVCG_LIST,
 457         },
 458 };
 459
 460 static int devcgroup_populate(struct cgroup_subsys *ss,
 461                                 struct cgroup *cgroup)
 462 {
 463         return cgroup_add_files(cgroup, ss, dev_cgroup_files,
 464                                         ARRAY_SIZE(dev_cgroup_files));
 465 }
 466
 467 struct cgroup_subsys devices_subsys = {
 468         .name = "devices",
 469         .can_attach = devcgroup_can_attach,
 470         .create = devcgroup_create,
 471         .destroy  = devcgroup_destroy,
 472         .populate = devcgroup_populate,
 473         .subsys_id = devices_subsys_id,
 474 };
 475
 476 int devcgroup_inode_permission(struct inode *inode, int mask)
 477 {
 478         struct dev_cgroup *dev_cgroup;
 479         struct dev_whitelist_item *wh;
 480
 481         dev_t device = inode->i_rdev;
 482         if (!device)
 483                 return 0;
 484         if (!S_ISBLK(inode->i_mode) && !S_ISCHR(inode->i_mode))
 485                 return 0;
 486
 487         rcu_read_lock();
 488
 489         dev_cgroup = task_devcgroup(current);
 490
 491         list_for_each_entry_rcu(wh, &dev_cgroup->whitelist, list) {
 492                 if (wh->type & DEV_ALL)
 493                         goto acc_check;
 494                 if ((wh->type & DEV_BLOCK) && !S_ISBLK(inode->i_mode))
 495                         continue;
 496                 if ((wh->type & DEV_CHAR) && !S_ISCHR(inode->i_mode))
 497                         continue;
 498                 if (wh->major != ~0 && wh->major != imajor(inode))
 499                         continue;
 500                 if (wh->minor != ~0 && wh->minor != iminor(inode))
 501                         continue;
 502 acc_check:
 503                 if ((mask & MAY_WRITE) && !(wh->access & ACC_WRITE))
 504                         continue;
 505                 if ((mask & MAY_READ) && !(wh->access & ACC_READ))
 506                         continue;
 507                 rcu_read_unlock();
 508                 return 0;
 509         }
 510
 511         rcu_read_unlock();
 512
 513         return -EPERM;
 514 }
 515
 516 int devcgroup_inode_mknod(int mode, dev_t dev)
 517 {
 518         struct dev_cgroup *dev_cgroup;
 519         struct dev_whitelist_item *wh;
 520
 521         if (!S_ISBLK(mode) && !S_ISCHR(mode))
 522                 return 0;
 523
 524         rcu_read_lock();
 525
 526         dev_cgroup = task_devcgroup(current);
 527
 528         list_for_each_entry_rcu(wh, &dev_cgroup->whitelist, list) {
 529                 if (wh->type & DEV_ALL)
 530                         goto acc_check;
 531                 if ((wh->type & DEV_BLOCK) && !S_ISBLK(mode))
 532                         continue;
 533                 if ((wh->type & DEV_CHAR) && !S_ISCHR(mode))
 534                         continue;
 535                 if (wh->major != ~0 && wh->major != MAJOR(dev))
 536                         continue;
 537                 if (wh->minor != ~0 && wh->minor != MINOR(dev))
 538                         continue;
 539 acc_check:
 540                 if (!(wh->access & ACC_MKNOD))
 541                         continue;
 542                 rcu_read_unlock();
 543                 return 0;
 544         }
 545
 546         rcu_read_unlock();
 547
 548         return -EPERM;
 549 }