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 *new_cgrp,
  65                                 struct cgroup_taskset *set)
  66 {
  67         struct task_struct *task = cgroup_taskset_first(set);
  68
  69         if (current != task && !capable(CAP_SYS_ADMIN))
  70                 return -EPERM;
  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 *cgroup)
 160 {
 161         struct dev_cgroup *dev_cgroup, *parent_dev_cgroup;
 162         struct cgroup *parent_cgroup;
 163         int ret;
 164
 165         dev_cgroup = kzalloc(sizeof(*dev_cgroup), GFP_KERNEL);
 166         if (!dev_cgroup)
 167                 return ERR_PTR(-ENOMEM);
 168         INIT_LIST_HEAD(&dev_cgroup->whitelist);
 169         parent_cgroup = cgroup->parent;
 170
 171         if (parent_cgroup == NULL) {
 172                 struct dev_whitelist_item *wh;
 173                 wh = kmalloc(sizeof(*wh), GFP_KERNEL);
 174                 if (!wh) {
 175                         kfree(dev_cgroup);
 176                         return ERR_PTR(-ENOMEM);
 177                 }
 178                 wh->minor = wh->major = ~0;
 179                 wh->type = DEV_ALL;
 180                 wh->access = ACC_MASK;
 181                 list_add(&wh->list, &dev_cgroup->whitelist);
 182         } else {
 183                 parent_dev_cgroup = cgroup_to_devcgroup(parent_cgroup);
 184                 mutex_lock(&devcgroup_mutex);
 185                 ret = dev_whitelist_copy(&dev_cgroup->whitelist,
 186                                 &parent_dev_cgroup->whitelist);
 187                 mutex_unlock(&devcgroup_mutex);
 188                 if (ret) {
 189                         kfree(dev_cgroup);
 190                         return ERR_PTR(ret);
 191                 }
 192         }
 193
 194         return &dev_cgroup->css;
 195 }
 196
 197 static void devcgroup_destroy(struct cgroup *cgroup)
 198 {
 199         struct dev_cgroup *dev_cgroup;
 200         struct dev_whitelist_item *wh, *tmp;
 201
 202         dev_cgroup = cgroup_to_devcgroup(cgroup);
 203         list_for_each_entry_safe(wh, tmp, &dev_cgroup->whitelist, list) {
 204                 list_del(&wh->list);
 205                 kfree(wh);
 206         }
 207         kfree(dev_cgroup);
 208 }
 209
 210 #define DEVCG_ALLOW 1
 211 #define DEVCG_DENY 2
 212 #define DEVCG_LIST 3
 213
 214 #define MAJMINLEN 13
 215 #define ACCLEN 4
 216
 217 static void set_access(char *acc, short access)
 218 {
 219         int idx = 0;
 220         memset(acc, 0, ACCLEN);
 221         if (access & ACC_READ)
 222                 acc[idx++] = 'r';
 223         if (access & ACC_WRITE)
 224                 acc[idx++] = 'w';
 225         if (access & ACC_MKNOD)
 226                 acc[idx++] = 'm';
 227 }
 228
 229 static char type_to_char(short type)
 230 {
 231         if (type == DEV_ALL)
 232                 return 'a';
 233         if (type == DEV_CHAR)
 234                 return 'c';
 235         if (type == DEV_BLOCK)
 236                 return 'b';
 237         return 'X';
 238 }
 239
 240 static void set_majmin(char *str, unsigned m)
 241 {
 242         if (m == ~0)
 243                 strcpy(str, "*");
 244         else
 245                 sprintf(str, "%u", m);
 246 }
 247
 248 static int devcgroup_seq_read(struct cgroup *cgroup, struct cftype *cft,
 249                                 struct seq_file *m)
 250 {
 251         struct dev_cgroup *devcgroup = cgroup_to_devcgroup(cgroup);
 252         struct dev_whitelist_item *wh;
 253         char maj[MAJMINLEN], min[MAJMINLEN], acc[ACCLEN];
 254
 255         rcu_read_lock();
 256         list_for_each_entry_rcu(wh, &devcgroup->whitelist, list) {
 257                 set_access(acc, wh->access);
 258                 set_majmin(maj, wh->major);
 259                 set_majmin(min, wh->minor);
 260                 seq_printf(m, "%c %s:%s %s\n", type_to_char(wh->type),
 261                            maj, min, acc);
 262         }
 263         rcu_read_unlock();
 264
 265         return 0;
 266 }
 267
 268 /*
 269  * may_access_whitelist:
 270  * does the access granted to dev_cgroup c contain the access
 271  * requested in whitelist item refwh.
 272  * return 1 if yes, 0 if no.
 273  * call with devcgroup_mutex held
 274  */
 275 static int may_access_whitelist(struct dev_cgroup *c,
 276                                        struct dev_whitelist_item *refwh)
 277 {
 278         struct dev_whitelist_item *whitem;
 279
 280         list_for_each_entry(whitem, &c->whitelist, list) {
 281                 if (whitem->type & DEV_ALL)
 282                         return 1;
 283                 if ((refwh->type & DEV_BLOCK) && !(whitem->type & DEV_BLOCK))
 284                         continue;
 285                 if ((refwh->type & DEV_CHAR) && !(whitem->type & DEV_CHAR))
 286                         continue;
 287                 if (whitem->major != ~0 && whitem->major != refwh->major)
 288                         continue;
 289                 if (whitem->minor != ~0 && whitem->minor != refwh->minor)
 290                         continue;
 291                 if (refwh->access & (~whitem->access))
 292                         continue;
 293                 return 1;
 294         }
 295         return 0;
 296 }
 297
 298 /*
 299  * parent_has_perm:
 300  * when adding a new allow rule to a device whitelist, the rule
 301  * must be allowed in the parent device
 302  */
 303 static int parent_has_perm(struct dev_cgroup *childcg,
 304                                   struct dev_whitelist_item *wh)
 305 {
 306         struct cgroup *pcg = childcg->css.cgroup->parent;
 307         struct dev_cgroup *parent;
 308
 309         if (!pcg)
 310                 return 1;
 311         parent = cgroup_to_devcgroup(pcg);
 312         return may_access_whitelist(parent, wh);
 313 }
 314
 315 /*
 316  * Modify the whitelist using allow/deny rules.
 317  * CAP_SYS_ADMIN is needed for this.  It's at least separate from CAP_MKNOD
 318  * so we can give a container CAP_MKNOD to let it create devices but not
 319  * modify the whitelist.
 320  * It seems likely we'll want to add a CAP_CONTAINER capability to allow
 321  * us to also grant CAP_SYS_ADMIN to containers without giving away the
 322  * device whitelist controls, but for now we'll stick with CAP_SYS_ADMIN
 323  *
 324  * Taking rules away is always allowed (given CAP_SYS_ADMIN).  Granting
 325  * new access is only allowed if you're in the top-level cgroup, or your
 326  * parent cgroup has the access you're asking for.
 327  */
 328 static int devcgroup_update_access(struct dev_cgroup *devcgroup,
 329                                    int filetype, const char *buffer)
 330 {
 331         const char *b;
 332         char *endp;
 333         int count;
 334         struct dev_whitelist_item wh;
 335
 336         if (!capable(CAP_SYS_ADMIN))
 337                 return -EPERM;
 338
 339         memset(&wh, 0, sizeof(wh));
 340         b = buffer;
 341
 342         switch (*b) {
 343         case 'a':
 344                 wh.type = DEV_ALL;
 345                 wh.access = ACC_MASK;
 346                 wh.major = ~0;
 347                 wh.minor = ~0;
 348                 goto handle;
 349         case 'b':
 350                 wh.type = DEV_BLOCK;
 351                 break;
 352         case 'c':
 353                 wh.type = DEV_CHAR;
 354                 break;
 355         default:
 356                 return -EINVAL;
 357         }
 358         b++;
 359         if (!isspace(*b))
 360                 return -EINVAL;
 361         b++;
 362         if (*b == '*') {
 363                 wh.major = ~0;
 364                 b++;
 365         } else if (isdigit(*b)) {
 366                 wh.major = simple_strtoul(b, &endp, 10);
 367                 b = endp;
 368         } else {
 369                 return -EINVAL;
 370         }
 371         if (*b != ':')
 372                 return -EINVAL;
 373         b++;
 374
 375         /* read minor */
 376         if (*b == '*') {
 377                 wh.minor = ~0;
 378                 b++;
 379         } else if (isdigit(*b)) {
 380                 wh.minor = simple_strtoul(b, &endp, 10);
 381                 b = endp;
 382         } else {
 383                 return -EINVAL;
 384         }
 385         if (!isspace(*b))
 386                 return -EINVAL;
 387         for (b++, count = 0; count < 3; count++, b++) {
 388                 switch (*b) {
 389                 case 'r':
 390                         wh.access |= ACC_READ;
 391                         break;
 392                 case 'w':
 393                         wh.access |= ACC_WRITE;
 394                         break;
 395                 case 'm':
 396                         wh.access |= ACC_MKNOD;
 397                         break;
 398                 case '\n':
 399                 case '\0':
 400                         count = 3;
 401                         break;
 402                 default:
 403                         return -EINVAL;
 404                 }
 405         }
 406
 407 handle:
 408         switch (filetype) {
 409         case DEVCG_ALLOW:
 410                 if (!parent_has_perm(devcgroup, &wh))
 411                         return -EPERM;
 412                 return dev_whitelist_add(devcgroup, &wh);
 413         case DEVCG_DENY:
 414                 dev_whitelist_rm(devcgroup, &wh);
 415                 break;
 416         default:
 417                 return -EINVAL;
 418         }
 419         return 0;
 420 }
 421
 422 static int devcgroup_access_write(struct cgroup *cgrp, struct cftype *cft,
 423                                   const char *buffer)
 424 {
 425         int retval;
 426
 427         mutex_lock(&devcgroup_mutex);
 428         retval = devcgroup_update_access(cgroup_to_devcgroup(cgrp),
 429                                          cft->private, buffer);
 430         mutex_unlock(&devcgroup_mutex);
 431         return retval;
 432 }
 433
 434 static struct cftype dev_cgroup_files[] = {
 435         {
 436                 .name = "allow",
 437                 .write_string  = devcgroup_access_write,
 438                 .private = DEVCG_ALLOW,
 439         },
 440         {
 441                 .name = "deny",
 442                 .write_string = devcgroup_access_write,
 443                 .private = DEVCG_DENY,
 444         },
 445         {
 446                 .name = "list",
 447                 .read_seq_string = devcgroup_seq_read,
 448                 .private = DEVCG_LIST,
 449         },
 450         { }     /* terminate */
 451 };
 452
 453 struct cgroup_subsys devices_subsys = {
 454         .name = "devices",
 455         .can_attach = devcgroup_can_attach,
 456         .create = devcgroup_create,
 457         .destroy = devcgroup_destroy,
 458         .subsys_id = devices_subsys_id,
 459         .base_cftypes = dev_cgroup_files,
 460
 461         /*
 462          * While devices cgroup has the rudimentary hierarchy support which
 463          * checks the parent's restriction, it doesn't properly propagates
 464          * config changes in ancestors to their descendents.  A child
 465          * should only be allowed to add more restrictions to the parent's
 466          * configuration.  Fix it and remove the following.
 467          */
 468         .broken_hierarchy = true,
 469 };
 470
 471 int __devcgroup_inode_permission(struct inode *inode, int mask)
 472 {
 473         struct dev_cgroup *dev_cgroup;
 474         struct dev_whitelist_item *wh;
 475
 476         rcu_read_lock();
 477
 478         dev_cgroup = task_devcgroup(current);
 479
 480         list_for_each_entry_rcu(wh, &dev_cgroup->whitelist, list) {
 481                 if (wh->type & DEV_ALL)
 482                         goto found;
 483                 if ((wh->type & DEV_BLOCK) && !S_ISBLK(inode->i_mode))
 484                         continue;
 485                 if ((wh->type & DEV_CHAR) && !S_ISCHR(inode->i_mode))
 486                         continue;
 487                 if (wh->major != ~0 && wh->major != imajor(inode))
 488                         continue;
 489                 if (wh->minor != ~0 && wh->minor != iminor(inode))
 490                         continue;
 491
 492                 if ((mask & MAY_WRITE) && !(wh->access & ACC_WRITE))
 493                         continue;
 494                 if ((mask & MAY_READ) && !(wh->access & ACC_READ))
 495                         continue;
 496 found:
 497                 rcu_read_unlock();
 498                 return 0;
 499         }
 500
 501         rcu_read_unlock();
 502
 503         return -EPERM;
 504 }
 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 }