linux/security/device_cgroup.c
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   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
  26static 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
  34struct 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
  42struct dev_cgroup {
  43        struct cgroup_subsys_state css;
  44        struct list_head whitelist;
  45};
  46
  47static inline struct dev_cgroup *css_to_devcgroup(struct cgroup_subsys_state *s)
  48{
  49        return container_of(s, struct dev_cgroup, css);
  50}
  51
  52static 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
  57static 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
  62struct cgroup_subsys devices_subsys;
  63
  64static int devcgroup_can_attach(struct cgroup_subsys *ss,
  65                        struct cgroup *new_cgrp, 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 */
  77static 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
  90free_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 */
 102static 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 */
 132static 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
 147remove:
 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 */
 159static 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
 198static 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
 219static 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
 231static 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
 242static void set_majmin(char *str, unsigned m)
 243{
 244        if (m == ~0)
 245                strcpy(str, "*");
 246        else
 247                sprintf(str, "%u", m);
 248}
 249
 250static 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 */
 277static 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 */
 305static 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 */
 330static 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
 409handle:
 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
 424static 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
 436static 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
 454static 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
 461struct 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
 470int __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;
 495found:
 496                rcu_read_unlock();
 497                return 0;
 498        }
 499
 500        rcu_read_unlock();
 501
 502        return -EPERM;
 503}
 504
 505int devcgroup_inode_mknod(int mode, dev_t dev)
 506{
 507        struct dev_cgroup *dev_cgroup;
 508        struct dev_whitelist_item *wh;
 509
 510        if (!S_ISBLK(mode) && !S_ISCHR(mode))
 511                return 0;
 512
 513        rcu_read_lock();
 514
 515        dev_cgroup = task_devcgroup(current);
 516
 517        list_for_each_entry_rcu(wh, &dev_cgroup->whitelist, list) {
 518                if (wh->type & DEV_ALL)
 519                        goto found;
 520                if ((wh->type & DEV_BLOCK) && !S_ISBLK(mode))
 521                        continue;
 522                if ((wh->type & DEV_CHAR) && !S_ISCHR(mode))
 523                        continue;
 524                if (wh->major != ~0 && wh->major != MAJOR(dev))
 525                        continue;
 526                if (wh->minor != ~0 && wh->minor != MINOR(dev))
 527                        continue;
 528
 529                if (!(wh->access & ACC_MKNOD))
 530                        continue;
 531found:
 532                rcu_read_unlock();
 533                return 0;
 534        }
 535
 536        rcu_read_unlock();
 537
 538        return -EPERM;
 539}
 540