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/rcupdate.h>
  14
  15#define ACC_MKNOD 1
  16#define ACC_READ  2
  17#define ACC_WRITE 4
  18#define ACC_MASK (ACC_MKNOD | ACC_READ | ACC_WRITE)
  19
  20#define DEV_BLOCK 1
  21#define DEV_CHAR  2
  22#define DEV_ALL   4  /* this represents all devices */
  23
  24/*
  25 * whitelist locking rules:
  26 * hold cgroup_lock() for update/read.
  27 * hold rcu_read_lock() for read.
  28 */
  29
  30struct dev_whitelist_item {
  31        u32 major, minor;
  32        short type;
  33        short access;
  34        struct list_head list;
  35        struct rcu_head rcu;
  36};
  37
  38struct dev_cgroup {
  39        struct cgroup_subsys_state css;
  40        struct list_head whitelist;
  41};
  42
  43static inline struct dev_cgroup *css_to_devcgroup(struct cgroup_subsys_state *s)
  44{
  45        return container_of(s, struct dev_cgroup, css);
  46}
  47
  48static inline struct dev_cgroup *cgroup_to_devcgroup(struct cgroup *cgroup)
  49{
  50        return css_to_devcgroup(cgroup_subsys_state(cgroup, devices_subsys_id));
  51}
  52
  53static inline struct dev_cgroup *task_devcgroup(struct task_struct *task)
  54{
  55        return css_to_devcgroup(task_subsys_state(task, devices_subsys_id));
  56}
  57
  58struct cgroup_subsys devices_subsys;
  59
  60static int devcgroup_can_attach(struct cgroup_subsys *ss,
  61                struct cgroup *new_cgroup, struct task_struct *task)
  62{
  63        if (current != task && !capable(CAP_SYS_ADMIN))
  64                        return -EPERM;
  65
  66        return 0;
  67}
  68
  69/*
  70 * called under cgroup_lock()
  71 */
  72static int dev_whitelist_copy(struct list_head *dest, struct list_head *orig)
  73{
  74        struct dev_whitelist_item *wh, *tmp, *new;
  75
  76        list_for_each_entry(wh, orig, list) {
  77                new = kmemdup(wh, sizeof(*wh), GFP_KERNEL);
  78                if (!new)
  79                        goto free_and_exit;
  80                list_add_tail(&new->list, dest);
  81        }
  82
  83        return 0;
  84
  85free_and_exit:
  86        list_for_each_entry_safe(wh, tmp, dest, list) {
  87                list_del(&wh->list);
  88                kfree(wh);
  89        }
  90        return -ENOMEM;
  91}
  92
  93/* Stupid prototype - don't bother combining existing entries */
  94/*
  95 * called under cgroup_lock()
  96 */
  97static int dev_whitelist_add(struct dev_cgroup *dev_cgroup,
  98                        struct dev_whitelist_item *wh)
  99{
 100        struct dev_whitelist_item *whcopy, *walk;
 101
 102        whcopy = kmemdup(wh, sizeof(*wh), GFP_KERNEL);
 103        if (!whcopy)
 104                return -ENOMEM;
 105
 106        list_for_each_entry(walk, &dev_cgroup->whitelist, list) {
 107                if (walk->type != wh->type)
 108                        continue;
 109                if (walk->major != wh->major)
 110                        continue;
 111                if (walk->minor != wh->minor)
 112                        continue;
 113
 114                walk->access |= wh->access;
 115                kfree(whcopy);
 116                whcopy = NULL;
 117        }
 118
 119        if (whcopy != NULL)
 120                list_add_tail_rcu(&whcopy->list, &dev_cgroup->whitelist);
 121        return 0;
 122}
 123
 124static void whitelist_item_free(struct rcu_head *rcu)
 125{
 126        struct dev_whitelist_item *item;
 127
 128        item = container_of(rcu, struct dev_whitelist_item, rcu);
 129        kfree(item);
 130}
 131
 132/*
 133 * called under cgroup_lock()
 134 */
 135static void dev_whitelist_rm(struct dev_cgroup *dev_cgroup,
 136                        struct dev_whitelist_item *wh)
 137{
 138        struct dev_whitelist_item *walk, *tmp;
 139
 140        list_for_each_entry_safe(walk, tmp, &dev_cgroup->whitelist, list) {
 141                if (walk->type == DEV_ALL)
 142                        goto remove;
 143                if (walk->type != wh->type)
 144                        continue;
 145                if (walk->major != ~0 && walk->major != wh->major)
 146                        continue;
 147                if (walk->minor != ~0 && walk->minor != wh->minor)
 148                        continue;
 149
 150remove:
 151                walk->access &= ~wh->access;
 152                if (!walk->access) {
 153                        list_del_rcu(&walk->list);
 154                        call_rcu(&walk->rcu, whitelist_item_free);
 155                }
 156        }
 157}
 158
 159/*
 160 * called from kernel/cgroup.c with cgroup_lock() held.
 161 */
 162static struct cgroup_subsys_state *devcgroup_create(struct cgroup_subsys *ss,
 163                                                struct cgroup *cgroup)
 164{
 165        struct dev_cgroup *dev_cgroup, *parent_dev_cgroup;
 166        struct cgroup *parent_cgroup;
 167        int ret;
 168
 169        dev_cgroup = kzalloc(sizeof(*dev_cgroup), GFP_KERNEL);
 170        if (!dev_cgroup)
 171                return ERR_PTR(-ENOMEM);
 172        INIT_LIST_HEAD(&dev_cgroup->whitelist);
 173        parent_cgroup = cgroup->parent;
 174
 175        if (parent_cgroup == NULL) {
 176                struct dev_whitelist_item *wh;
 177                wh = kmalloc(sizeof(*wh), GFP_KERNEL);
 178                if (!wh) {
 179                        kfree(dev_cgroup);
 180                        return ERR_PTR(-ENOMEM);
 181                }
 182                wh->minor = wh->major = ~0;
 183                wh->type = DEV_ALL;
 184                wh->access = ACC_MASK;
 185                list_add(&wh->list, &dev_cgroup->whitelist);
 186        } else {
 187                parent_dev_cgroup = cgroup_to_devcgroup(parent_cgroup);
 188                ret = dev_whitelist_copy(&dev_cgroup->whitelist,
 189                                &parent_dev_cgroup->whitelist);
 190                if (ret) {
 191                        kfree(dev_cgroup);
 192                        return ERR_PTR(ret);
 193                }
 194        }
 195
 196        return &dev_cgroup->css;
 197}
 198
 199static void devcgroup_destroy(struct cgroup_subsys *ss,
 200                        struct cgroup *cgroup)
 201{
 202        struct dev_cgroup *dev_cgroup;
 203        struct dev_whitelist_item *wh, *tmp;
 204
 205        dev_cgroup = cgroup_to_devcgroup(cgroup);
 206        list_for_each_entry_safe(wh, tmp, &dev_cgroup->whitelist, list) {
 207                list_del(&wh->list);
 208                kfree(wh);
 209        }
 210        kfree(dev_cgroup);
 211}
 212
 213#define DEVCG_ALLOW 1
 214#define DEVCG_DENY 2
 215#define DEVCG_LIST 3
 216
 217#define MAJMINLEN 13
 218#define ACCLEN 4
 219
 220static void set_access(char *acc, short access)
 221{
 222        int idx = 0;
 223        memset(acc, 0, ACCLEN);
 224        if (access & ACC_READ)
 225                acc[idx++] = 'r';
 226        if (access & ACC_WRITE)
 227                acc[idx++] = 'w';
 228        if (access & ACC_MKNOD)
 229                acc[idx++] = 'm';
 230}
 231
 232static char type_to_char(short type)
 233{
 234        if (type == DEV_ALL)
 235                return 'a';
 236        if (type == DEV_CHAR)
 237                return 'c';
 238        if (type == DEV_BLOCK)
 239                return 'b';
 240        return 'X';
 241}
 242
 243static void set_majmin(char *str, unsigned m)
 244{
 245        if (m == ~0)
 246                strcpy(str, "*");
 247        else
 248                sprintf(str, "%u", m);
 249}
 250
 251static int devcgroup_seq_read(struct cgroup *cgroup, struct cftype *cft,
 252                                struct seq_file *m)
 253{
 254        struct dev_cgroup *devcgroup = cgroup_to_devcgroup(cgroup);
 255        struct dev_whitelist_item *wh;
 256        char maj[MAJMINLEN], min[MAJMINLEN], acc[ACCLEN];
 257
 258        rcu_read_lock();
 259        list_for_each_entry_rcu(wh, &devcgroup->whitelist, list) {
 260                set_access(acc, wh->access);
 261                set_majmin(maj, wh->major);
 262                set_majmin(min, wh->minor);
 263                seq_printf(m, "%c %s:%s %s\n", type_to_char(wh->type),
 264                           maj, min, acc);
 265        }
 266        rcu_read_unlock();
 267
 268        return 0;
 269}
 270
 271/*
 272 * may_access_whitelist:
 273 * does the access granted to dev_cgroup c contain the access
 274 * requested in whitelist item refwh.
 275 * return 1 if yes, 0 if no.
 276 * call with c->lock held
 277 */
 278static int may_access_whitelist(struct dev_cgroup *c,
 279                                       struct dev_whitelist_item *refwh)
 280{
 281        struct dev_whitelist_item *whitem;
 282
 283        list_for_each_entry(whitem, &c->whitelist, list) {
 284                if (whitem->type & DEV_ALL)
 285                        return 1;
 286                if ((refwh->type & DEV_BLOCK) && !(whitem->type & DEV_BLOCK))
 287                        continue;
 288                if ((refwh->type & DEV_CHAR) && !(whitem->type & DEV_CHAR))
 289                        continue;
 290                if (whitem->major != ~0 && whitem->major != refwh->major)
 291                        continue;
 292                if (whitem->minor != ~0 && whitem->minor != refwh->minor)
 293                        continue;
 294                if (refwh->access & (~whitem->access))
 295                        continue;
 296                return 1;
 297        }
 298        return 0;
 299}
 300
 301/*
 302 * parent_has_perm:
 303 * when adding a new allow rule to a device whitelist, the rule
 304 * must be allowed in the parent device
 305 */
 306static int parent_has_perm(struct dev_cgroup *childcg,
 307                                  struct dev_whitelist_item *wh)
 308{
 309        struct cgroup *pcg = childcg->css.cgroup->parent;
 310        struct dev_cgroup *parent;
 311
 312        if (!pcg)
 313                return 1;
 314        parent = cgroup_to_devcgroup(pcg);
 315        return may_access_whitelist(parent, wh);
 316}
 317
 318/*
 319 * Modify the whitelist using allow/deny rules.
 320 * CAP_SYS_ADMIN is needed for this.  It's at least separate from CAP_MKNOD
 321 * so we can give a container CAP_MKNOD to let it create devices but not
 322 * modify the whitelist.
 323 * It seems likely we'll want to add a CAP_CONTAINER capability to allow
 324 * us to also grant CAP_SYS_ADMIN to containers without giving away the
 325 * device whitelist controls, but for now we'll stick with CAP_SYS_ADMIN
 326 *
 327 * Taking rules away is always allowed (given CAP_SYS_ADMIN).  Granting
 328 * new access is only allowed if you're in the top-level cgroup, or your
 329 * parent cgroup has the access you're asking for.
 330 */
 331static int devcgroup_update_access(struct dev_cgroup *devcgroup,
 332                                   int filetype, const char *buffer)
 333{
 334        const char *b;
 335        char *endp;
 336        int count;
 337        struct dev_whitelist_item wh;
 338
 339        if (!capable(CAP_SYS_ADMIN))
 340                return -EPERM;
 341
 342        memset(&wh, 0, sizeof(wh));
 343        b = buffer;
 344
 345        switch (*b) {
 346        case 'a':
 347                wh.type = DEV_ALL;
 348                wh.access = ACC_MASK;
 349                wh.major = ~0;
 350                wh.minor = ~0;
 351                goto handle;
 352        case 'b':
 353                wh.type = DEV_BLOCK;
 354                break;
 355        case 'c':
 356                wh.type = DEV_CHAR;
 357                break;
 358        default:
 359                return -EINVAL;
 360        }
 361        b++;
 362        if (!isspace(*b))
 363                return -EINVAL;
 364        b++;
 365        if (*b == '*') {
 366                wh.major = ~0;
 367                b++;
 368        } else if (isdigit(*b)) {
 369                wh.major = simple_strtoul(b, &endp, 10);
 370                b = endp;
 371        } else {
 372                return -EINVAL;
 373        }
 374        if (*b != ':')
 375                return -EINVAL;
 376        b++;
 377
 378        /* read minor */
 379        if (*b == '*') {
 380                wh.minor = ~0;
 381                b++;
 382        } else if (isdigit(*b)) {
 383                wh.minor = simple_strtoul(b, &endp, 10);
 384                b = endp;
 385        } else {
 386                return -EINVAL;
 387        }
 388        if (!isspace(*b))
 389                return -EINVAL;
 390        for (b++, count = 0; count < 3; count++, b++) {
 391                switch (*b) {
 392                case 'r':
 393                        wh.access |= ACC_READ;
 394                        break;
 395                case 'w':
 396                        wh.access |= ACC_WRITE;
 397                        break;
 398                case 'm':
 399                        wh.access |= ACC_MKNOD;
 400                        break;
 401                case '\n':
 402                case '\0':
 403                        count = 3;
 404                        break;
 405                default:
 406                        return -EINVAL;
 407                }
 408        }
 409
 410handle:
 411        switch (filetype) {
 412        case DEVCG_ALLOW:
 413                if (!parent_has_perm(devcgroup, &wh))
 414                        return -EPERM;
 415                return dev_whitelist_add(devcgroup, &wh);
 416        case DEVCG_DENY:
 417                dev_whitelist_rm(devcgroup, &wh);
 418                break;
 419        default:
 420                return -EINVAL;
 421        }
 422        return 0;
 423}
 424
 425static int devcgroup_access_write(struct cgroup *cgrp, struct cftype *cft,
 426                                  const char *buffer)
 427{
 428        int retval;
 429        if (!cgroup_lock_live_group(cgrp))
 430                return -ENODEV;
 431        retval = devcgroup_update_access(cgroup_to_devcgroup(cgrp),
 432                                         cft->private, buffer);
 433        cgroup_unlock();
 434        return retval;
 435}
 436
 437static struct cftype dev_cgroup_files[] = {
 438        {
 439                .name = "allow",
 440                .write_string  = devcgroup_access_write,
 441                .private = DEVCG_ALLOW,
 442        },
 443        {
 444                .name = "deny",
 445                .write_string = devcgroup_access_write,
 446                .private = DEVCG_DENY,
 447        },
 448        {
 449                .name = "list",
 450                .read_seq_string = devcgroup_seq_read,
 451                .private = DEVCG_LIST,
 452        },
 453};
 454
 455static int devcgroup_populate(struct cgroup_subsys *ss,
 456                                struct cgroup *cgroup)
 457{
 458        return cgroup_add_files(cgroup, ss, dev_cgroup_files,
 459                                        ARRAY_SIZE(dev_cgroup_files));
 460}
 461
 462struct cgroup_subsys devices_subsys = {
 463        .name = "devices",
 464        .can_attach = devcgroup_can_attach,
 465        .create = devcgroup_create,
 466        .destroy  = devcgroup_destroy,
 467        .populate = devcgroup_populate,
 468        .subsys_id = devices_subsys_id,
 469};
 470
 471int devcgroup_inode_permission(struct inode *inode, int mask)
 472{
 473        struct dev_cgroup *dev_cgroup;
 474        struct dev_whitelist_item *wh;
 475
 476        dev_t device = inode->i_rdev;
 477        if (!device)
 478                return 0;
 479        if (!S_ISBLK(inode->i_mode) && !S_ISCHR(inode->i_mode))
 480                return 0;
 481
 482        rcu_read_lock();
 483
 484        dev_cgroup = task_devcgroup(current);
 485
 486        list_for_each_entry_rcu(wh, &dev_cgroup->whitelist, list) {
 487                if (wh->type & DEV_ALL)
 488                        goto acc_check;
 489                if ((wh->type & DEV_BLOCK) && !S_ISBLK(inode->i_mode))
 490                        continue;
 491                if ((wh->type & DEV_CHAR) && !S_ISCHR(inode->i_mode))
 492                        continue;
 493                if (wh->major != ~0 && wh->major != imajor(inode))
 494                        continue;
 495                if (wh->minor != ~0 && wh->minor != iminor(inode))
 496                        continue;
 497acc_check:
 498                if ((mask & MAY_WRITE) && !(wh->access & ACC_WRITE))
 499                        continue;
 500                if ((mask & MAY_READ) && !(wh->access & ACC_READ))
 501                        continue;
 502                rcu_read_unlock();
 503                return 0;
 504        }
 505
 506        rcu_read_unlock();
 507
 508        return -EPERM;
 509}
 510
 511int devcgroup_inode_mknod(int mode, dev_t dev)
 512{
 513        struct dev_cgroup *dev_cgroup;
 514        struct dev_whitelist_item *wh;
 515
 516        if (!S_ISBLK(mode) && !S_ISCHR(mode))
 517                return 0;
 518
 519        rcu_read_lock();
 520
 521        dev_cgroup = task_devcgroup(current);
 522
 523        list_for_each_entry(wh, &dev_cgroup->whitelist, list) {
 524                if (wh->type & DEV_ALL)
 525                        goto acc_check;
 526                if ((wh->type & DEV_BLOCK) && !S_ISBLK(mode))
 527                        continue;
 528                if ((wh->type & DEV_CHAR) && !S_ISCHR(mode))
 529                        continue;
 530                if (wh->major != ~0 && wh->major != MAJOR(dev))
 531                        continue;
 532                if (wh->minor != ~0 && wh->minor != MINOR(dev))
 533                        continue;
 534acc_check:
 535                if (!(wh->access & ACC_MKNOD))
 536                        continue;
 537                rcu_read_unlock();
 538                return 0;
 539        }
 540
 541        rcu_read_unlock();
 542
 543        return -EPERM;
 544}
 545