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