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#include <linux/mutex.h>
  15
  16#define ACC_MKNOD 1
  17#define ACC_READ  2
  18#define ACC_WRITE 4
  19#define ACC_MASK (ACC_MKNOD | ACC_READ | ACC_WRITE)
  20
  21#define DEV_BLOCK 1
  22#define DEV_CHAR  2
  23#define DEV_ALL   4  /* this represents all devices */
  24
  25static DEFINE_MUTEX(devcgroup_mutex);
  26
  27/*
  28 * whitelist locking rules:
  29 * hold devcgroup_mutex for update/read.
  30 * hold rcu_read_lock() for read.
  31 */
  32
  33struct dev_whitelist_item {
  34        u32 major, minor;
  35        short type;
  36        short access;
  37        struct list_head list;
  38        struct rcu_head rcu;
  39};
  40
  41struct dev_cgroup {
  42        struct cgroup_subsys_state css;
  43        struct list_head whitelist;
  44};
  45
  46static inline struct dev_cgroup *css_to_devcgroup(struct cgroup_subsys_state *s)
  47{
  48        return container_of(s, struct dev_cgroup, css);
  49}
  50
  51static inline struct dev_cgroup *cgroup_to_devcgroup(struct cgroup *cgroup)
  52{
  53        return css_to_devcgroup(cgroup_subsys_state(cgroup, devices_subsys_id));
  54}
  55
  56static inline struct dev_cgroup *task_devcgroup(struct task_struct *task)
  57{
  58        return css_to_devcgroup(task_subsys_state(task, devices_subsys_id));
  59}
  60
  61struct cgroup_subsys devices_subsys;
  62
  63static int devcgroup_can_attach(struct cgroup_subsys *ss,
  64                struct cgroup *new_cgroup, struct task_struct *task)
  65{
  66        if (current != task && !capable(CAP_SYS_ADMIN))
  67                        return -EPERM;
  68
  69        return 0;
  70}
  71
  72/*
  73 * called under devcgroup_mutex
  74 */
  75static int dev_whitelist_copy(struct list_head *dest, struct list_head *orig)
  76{
  77        struct dev_whitelist_item *wh, *tmp, *new;
  78
  79        list_for_each_entry(wh, orig, list) {
  80                new = kmemdup(wh, sizeof(*wh), GFP_KERNEL);
  81                if (!new)
  82                        goto free_and_exit;
  83                list_add_tail(&new->list, dest);
  84        }
  85
  86        return 0;
  87
  88free_and_exit:
  89        list_for_each_entry_safe(wh, tmp, dest, list) {
  90                list_del(&wh->list);
  91                kfree(wh);
  92        }
  93        return -ENOMEM;
  94}
  95
  96/* Stupid prototype - don't bother combining existing entries */
  97/*
  98 * called under devcgroup_mutex
  99 */
 100static int dev_whitelist_add(struct dev_cgroup *dev_cgroup,
 101                        struct dev_whitelist_item *wh)
 102{
 103        struct dev_whitelist_item *whcopy, *walk;
 104
 105        whcopy = kmemdup(wh, sizeof(*wh), GFP_KERNEL);
 106        if (!whcopy)
 107                return -ENOMEM;
 108
 109        list_for_each_entry(walk, &dev_cgroup->whitelist, list) {
 110                if (walk->type != wh->type)
 111                        continue;
 112                if (walk->major != wh->major)
 113                        continue;
 114                if (walk->minor != wh->minor)
 115                        continue;
 116
 117                walk->access |= wh->access;
 118                kfree(whcopy);
 119                whcopy = NULL;
 120        }
 121
 122        if (whcopy != NULL)
 123                list_add_tail_rcu(&whcopy->list, &dev_cgroup->whitelist);
 124        return 0;
 125}
 126
 127static void whitelist_item_free(struct rcu_head *rcu)
 128{
 129        struct dev_whitelist_item *item;
 130
 131        item = container_of(rcu, struct dev_whitelist_item, rcu);
 132        kfree(item);
 133}
 134
 135/*
 136 * called under devcgroup_mutex
 137 */
 138static void dev_whitelist_rm(struct dev_cgroup *dev_cgroup,
 139                        struct dev_whitelist_item *wh)
 140{
 141        struct dev_whitelist_item *walk, *tmp;
 142
 143        list_for_each_entry_safe(walk, tmp, &dev_cgroup->whitelist, list) {
 144                if (walk->type == DEV_ALL)
 145                        goto remove;
 146                if (walk->type != wh->type)
 147                        continue;
 148                if (walk->major != ~0 && walk->major != wh->major)
 149                        continue;
 150                if (walk->minor != ~0 && walk->minor != wh->minor)
 151                        continue;
 152
 153remove:
 154                walk->access &= ~wh->access;
 155                if (!walk->access) {
 156                        list_del_rcu(&walk->list);
 157                        call_rcu(&walk->rcu, whitelist_item_free);
 158                }
 159        }
 160}
 161
 162/*
 163 * called from kernel/cgroup.c with cgroup_lock() held.
 164 */
 165static struct cgroup_subsys_state *devcgroup_create(struct cgroup_subsys *ss,
 166                                                struct cgroup *cgroup)
 167{
 168        struct dev_cgroup *dev_cgroup, *parent_dev_cgroup;
 169        struct cgroup *parent_cgroup;
 170        int ret;
 171
 172        dev_cgroup = kzalloc(sizeof(*dev_cgroup), GFP_KERNEL);
 173        if (!dev_cgroup)
 174                return ERR_PTR(-ENOMEM);
 175        INIT_LIST_HEAD(&dev_cgroup->whitelist);
 176        parent_cgroup = cgroup->parent;
 177
 178        if (parent_cgroup == NULL) {
 179                struct dev_whitelist_item *wh;
 180                wh = kmalloc(sizeof(*wh), GFP_KERNEL);
 181                if (!wh) {
 182                        kfree(dev_cgroup);
 183                        return ERR_PTR(-ENOMEM);
 184                }
 185                wh->minor = wh->major = ~0;
 186                wh->type = DEV_ALL;
 187                wh->access = ACC_MASK;
 188                list_add(&wh->list, &dev_cgroup->whitelist);
 189        } else {
 190                parent_dev_cgroup = cgroup_to_devcgroup(parent_cgroup);
 191                mutex_lock(&devcgroup_mutex);
 192                ret = dev_whitelist_copy(&dev_cgroup->whitelist,
 193                                &parent_dev_cgroup->whitelist);
 194                mutex_unlock(&devcgroup_mutex);
 195                if (ret) {
 196                        kfree(dev_cgroup);
 197                        return ERR_PTR(ret);
 198                }
 199        }
 200
 201        return &dev_cgroup->css;
 202}
 203
 204static void devcgroup_destroy(struct cgroup_subsys *ss,
 205                        struct cgroup *cgroup)
 206{
 207        struct dev_cgroup *dev_cgroup;
 208        struct dev_whitelist_item *wh, *tmp;
 209
 210        dev_cgroup = cgroup_to_devcgroup(cgroup);
 211        list_for_each_entry_safe(wh, tmp, &dev_cgroup->whitelist, list) {
 212                list_del(&wh->list);
 213                kfree(wh);
 214        }
 215        kfree(dev_cgroup);
 216}
 217
 218#define DEVCG_ALLOW 1
 219#define DEVCG_DENY 2
 220#define DEVCG_LIST 3
 221
 222#define MAJMINLEN 13
 223#define ACCLEN 4
 224
 225static void set_access(char *acc, short access)
 226{
 227        int idx = 0;
 228        memset(acc, 0, ACCLEN);
 229        if (access & ACC_READ)
 230                acc[idx++] = 'r';
 231        if (access & ACC_WRITE)
 232                acc[idx++] = 'w';
 233        if (access & ACC_MKNOD)
 234                acc[idx++] = 'm';
 235}
 236
 237static char type_to_char(short type)
 238{
 239        if (type == DEV_ALL)
 240                return 'a';
 241        if (type == DEV_CHAR)
 242                return 'c';
 243        if (type == DEV_BLOCK)
 244                return 'b';
 245        return 'X';
 246}
 247
 248static void set_majmin(char *str, unsigned m)
 249{
 250        if (m == ~0)
 251                strcpy(str, "*");
 252        else
 253                sprintf(str, "%u", m);
 254}
 255
 256static int devcgroup_seq_read(struct cgroup *cgroup, struct cftype *cft,
 257                                struct seq_file *m)
 258{
 259        struct dev_cgroup *devcgroup = cgroup_to_devcgroup(cgroup);
 260        struct dev_whitelist_item *wh;
 261        char maj[MAJMINLEN], min[MAJMINLEN], acc[ACCLEN];
 262
 263        rcu_read_lock();
 264        list_for_each_entry_rcu(wh, &devcgroup->whitelist, list) {
 265                set_access(acc, wh->access);
 266                set_majmin(maj, wh->major);
 267                set_majmin(min, wh->minor);
 268                seq_printf(m, "%c %s:%s %s\n", type_to_char(wh->type),
 269                           maj, min, acc);
 270        }
 271        rcu_read_unlock();
 272
 273        return 0;
 274}
 275
 276/*
 277 * may_access_whitelist:
 278 * does the access granted to dev_cgroup c contain the access
 279 * requested in whitelist item refwh.
 280 * return 1 if yes, 0 if no.
 281 * call with devcgroup_mutex held
 282 */
 283static int may_access_whitelist(struct dev_cgroup *c,
 284                                       struct dev_whitelist_item *refwh)
 285{
 286        struct dev_whitelist_item *whitem;
 287
 288        list_for_each_entry(whitem, &c->whitelist, list) {
 289                if (whitem->type & DEV_ALL)
 290                        return 1;
 291                if ((refwh->type & DEV_BLOCK) && !(whitem->type & DEV_BLOCK))
 292                        continue;
 293                if ((refwh->type & DEV_CHAR) && !(whitem->type & DEV_CHAR))
 294                        continue;
 295                if (whitem->major != ~0 && whitem->major != refwh->major)
 296                        continue;
 297                if (whitem->minor != ~0 && whitem->minor != refwh->minor)
 298                        continue;
 299                if (refwh->access & (~whitem->access))
 300                        continue;
 301                return 1;
 302        }
 303        return 0;
 304}
 305
 306/*
 307 * parent_has_perm:
 308 * when adding a new allow rule to a device whitelist, the rule
 309 * must be allowed in the parent device
 310 */
 311static int parent_has_perm(struct dev_cgroup *childcg,
 312                                  struct dev_whitelist_item *wh)
 313{
 314        struct cgroup *pcg = childcg->css.cgroup->parent;
 315        struct dev_cgroup *parent;
 316
 317        if (!pcg)
 318                return 1;
 319        parent = cgroup_to_devcgroup(pcg);
 320        return may_access_whitelist(parent, wh);
 321}
 322
 323/*
 324 * Modify the whitelist using allow/deny rules.
 325 * CAP_SYS_ADMIN is needed for this.  It's at least separate from CAP_MKNOD
 326 * so we can give a container CAP_MKNOD to let it create devices but not
 327 * modify the whitelist.
 328 * It seems likely we'll want to add a CAP_CONTAINER capability to allow
 329 * us to also grant CAP_SYS_ADMIN to containers without giving away the
 330 * device whitelist controls, but for now we'll stick with CAP_SYS_ADMIN
 331 *
 332 * Taking rules away is always allowed (given CAP_SYS_ADMIN).  Granting
 333 * new access is only allowed if you're in the top-level cgroup, or your
 334 * parent cgroup has the access you're asking for.
 335 */
 336static int devcgroup_update_access(struct dev_cgroup *devcgroup,
 337                                   int filetype, const char *buffer)
 338{
 339        const char *b;
 340        char *endp;
 341        int count;
 342        struct dev_whitelist_item wh;
 343
 344        if (!capable(CAP_SYS_ADMIN))
 345                return -EPERM;
 346
 347        memset(&wh, 0, sizeof(wh));
 348        b = buffer;
 349
 350        switch (*b) {
 351        case 'a':
 352                wh.type = DEV_ALL;
 353                wh.access = ACC_MASK;
 354                wh.major = ~0;
 355                wh.minor = ~0;
 356                goto handle;
 357        case 'b':
 358                wh.type = DEV_BLOCK;
 359                break;
 360        case 'c':
 361                wh.type = DEV_CHAR;
 362                break;
 363        default:
 364                return -EINVAL;
 365        }
 366        b++;
 367        if (!isspace(*b))
 368                return -EINVAL;
 369        b++;
 370        if (*b == '*') {
 371                wh.major = ~0;
 372                b++;
 373        } else if (isdigit(*b)) {
 374                wh.major = simple_strtoul(b, &endp, 10);
 375                b = endp;
 376        } else {
 377                return -EINVAL;
 378        }
 379        if (*b != ':')
 380                return -EINVAL;
 381        b++;
 382
 383        /* read minor */
 384        if (*b == '*') {
 385                wh.minor = ~0;
 386                b++;
 387        } else if (isdigit(*b)) {
 388                wh.minor = simple_strtoul(b, &endp, 10);
 389                b = endp;
 390        } else {
 391                return -EINVAL;
 392        }
 393        if (!isspace(*b))
 394                return -EINVAL;
 395        for (b++, count = 0; count < 3; count++, b++) {
 396                switch (*b) {
 397                case 'r':
 398                        wh.access |= ACC_READ;
 399                        break;
 400                case 'w':
 401                        wh.access |= ACC_WRITE;
 402                        break;
 403                case 'm':
 404                        wh.access |= ACC_MKNOD;
 405                        break;
 406                case '\n':
 407                case '\0':
 408                        count = 3;
 409                        break;
 410                default:
 411                        return -EINVAL;
 412                }
 413        }
 414
 415handle:
 416        switch (filetype) {
 417        case DEVCG_ALLOW:
 418                if (!parent_has_perm(devcgroup, &wh))
 419                        return -EPERM;
 420                return dev_whitelist_add(devcgroup, &wh);
 421        case DEVCG_DENY:
 422                dev_whitelist_rm(devcgroup, &wh);
 423                break;
 424        default:
 425                return -EINVAL;
 426        }
 427        return 0;
 428}
 429
 430static int devcgroup_access_write(struct cgroup *cgrp, struct cftype *cft,
 431                                  const char *buffer)
 432{
 433        int retval;
 434
 435        mutex_lock(&devcgroup_mutex);
 436        retval = devcgroup_update_access(cgroup_to_devcgroup(cgrp),
 437                                         cft->private, buffer);
 438        mutex_unlock(&devcgroup_mutex);
 439        return retval;
 440}
 441
 442static struct cftype dev_cgroup_files[] = {
 443        {
 444                .name = "allow",
 445                .write_string  = devcgroup_access_write,
 446                .private = DEVCG_ALLOW,
 447        },
 448        {
 449                .name = "deny",
 450                .write_string = devcgroup_access_write,
 451                .private = DEVCG_DENY,
 452        },
 453        {
 454                .name = "list",
 455                .read_seq_string = devcgroup_seq_read,
 456                .private = DEVCG_LIST,
 457        },
 458};
 459
 460static int devcgroup_populate(struct cgroup_subsys *ss,
 461                                struct cgroup *cgroup)
 462{
 463        return cgroup_add_files(cgroup, ss, dev_cgroup_files,
 464                                        ARRAY_SIZE(dev_cgroup_files));
 465}
 466
 467struct cgroup_subsys devices_subsys = {
 468        .name = "devices",
 469        .can_attach = devcgroup_can_attach,
 470        .create = devcgroup_create,
 471        .destroy  = devcgroup_destroy,
 472        .populate = devcgroup_populate,
 473        .subsys_id = devices_subsys_id,
 474};
 475
 476int devcgroup_inode_permission(struct inode *inode, int mask)
 477{
 478        struct dev_cgroup *dev_cgroup;
 479        struct dev_whitelist_item *wh;
 480
 481        dev_t device = inode->i_rdev;
 482        if (!device)
 483                return 0;
 484        if (!S_ISBLK(inode->i_mode) && !S_ISCHR(inode->i_mode))
 485                return 0;
 486
 487        rcu_read_lock();
 488
 489        dev_cgroup = task_devcgroup(current);
 490
 491        list_for_each_entry_rcu(wh, &dev_cgroup->whitelist, list) {
 492                if (wh->type & DEV_ALL)
 493                        goto acc_check;
 494                if ((wh->type & DEV_BLOCK) && !S_ISBLK(inode->i_mode))
 495                        continue;
 496                if ((wh->type & DEV_CHAR) && !S_ISCHR(inode->i_mode))
 497                        continue;
 498                if (wh->major != ~0 && wh->major != imajor(inode))
 499                        continue;
 500                if (wh->minor != ~0 && wh->minor != iminor(inode))
 501                        continue;
 502acc_check:
 503                if ((mask & MAY_WRITE) && !(wh->access & ACC_WRITE))
 504                        continue;
 505                if ((mask & MAY_READ) && !(wh->access & ACC_READ))
 506                        continue;
 507                rcu_read_unlock();
 508                return 0;
 509        }
 510
 511        rcu_read_unlock();
 512
 513        return -EPERM;
 514}
 515
 516int devcgroup_inode_mknod(int mode, dev_t dev)
 517{
 518        struct dev_cgroup *dev_cgroup;
 519        struct dev_whitelist_item *wh;
 520
 521        if (!S_ISBLK(mode) && !S_ISCHR(mode))
 522                return 0;
 523
 524        rcu_read_lock();
 525
 526        dev_cgroup = task_devcgroup(current);
 527
 528        list_for_each_entry_rcu(wh, &dev_cgroup->whitelist, list) {
 529                if (wh->type & DEV_ALL)
 530                        goto acc_check;
 531                if ((wh->type & DEV_BLOCK) && !S_ISBLK(mode))
 532                        continue;
 533                if ((wh->type & DEV_CHAR) && !S_ISCHR(mode))
 534                        continue;
 535                if (wh->major != ~0 && wh->major != MAJOR(dev))
 536                        continue;
 537                if (wh->minor != ~0 && wh->minor != MINOR(dev))
 538                        continue;
 539acc_check:
 540                if (!(wh->access & ACC_MKNOD))
 541                        continue;
 542                rcu_read_unlock();
 543                return 0;
 544        }
 545
 546        rcu_read_unlock();
 547
 548        return -EPERM;
 549}
 550