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