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
  26 static 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
  34 struct 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
  42 struct dev_cgroup {
  43         struct cgroup_subsys_state css;
  44         struct list_head whitelist;
  45 };
  46
  47 static inline struct dev_cgroup *css_to_devcgroup(struct cgroup_subsys_state *s)
  48 {
  49         return container_of(s, struct dev_cgroup, css);
  50 }
  51
  52 static 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
  57 static 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
  62 struct cgroup_subsys devices_subsys;
  63
  64 static 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  */
  77 static 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
  90 free_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  */
 102 static 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 static 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  */
 140 static 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
 155 remove:
 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  */
 167 static 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
 206 static 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
 227 static 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
 239 static 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
 250 static void set_majmin(char *str, unsigned m)
 251 {
 252         if (m == ~0)
 253                 strcpy(str, "*");
 254         else
 255                 sprintf(str, "%u", m);
 256 }
 257
 258 static 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  */
 285 static 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  */
 313 static 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  */
 338 static 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
 417 handle:
 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
 432 static 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
 444 static 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
 462 static 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
 469 struct 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
 478 int 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;
 509 found:
 510                 rcu_read_unlock();
 511                 return 0;
 512         }
 513
 514         rcu_read_unlock();
 515
 516         return -EPERM;
 517 }
 518
 519 int 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;
 545 found:
 546                 rcu_read_unlock();
 547                 return 0;
 548         }
 549
 550         rcu_read_unlock();
 551
 552         return -EPERM;
 553 }