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