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