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