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 *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 */
  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 *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
 197static 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
 217static 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
 229static 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
 240static void set_majmin(char *str, unsigned m)
 241{
 242        if (m == ~0)
 243                strcpy(str, "*");
 244        else
 245                sprintf(str, "%u", m);
 246}
 247
 248static 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 */
 275static 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 */
 303static 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 */
 328static 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
 407handle:
 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
 422static 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
 434static 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
 453struct 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
 462int __devcgroup_inode_permission(struct inode *inode, int mask)
 463{
 464        struct dev_cgroup *dev_cgroup;
 465        struct dev_whitelist_item *wh;
 466
 467        rcu_read_lock();
 468
 469        dev_cgroup = task_devcgroup(current);
 470
 471        list_for_each_entry_rcu(wh, &dev_cgroup->whitelist, list) {
 472                if (wh->type & DEV_ALL)
 473                        goto found;
 474                if ((wh->type & DEV_BLOCK) && !S_ISBLK(inode->i_mode))
 475                        continue;
 476                if ((wh->type & DEV_CHAR) && !S_ISCHR(inode->i_mode))
 477                        continue;
 478                if (wh->major != ~0 && wh->major != imajor(inode))
 479                        continue;
 480                if (wh->minor != ~0 && wh->minor != iminor(inode))
 481                        continue;
 482
 483                if ((mask & MAY_WRITE) && !(wh->access & ACC_WRITE))
 484                        continue;
 485                if ((mask & MAY_READ) && !(wh->access & ACC_READ))
 486                        continue;
 487found:
 488                rcu_read_unlock();
 489                return 0;
 490        }
 491
 492        rcu_read_unlock();
 493
 494        return -EPERM;
 495}
 496
 497int devcgroup_inode_mknod(int mode, dev_t dev)
 498{
 499        struct dev_cgroup *dev_cgroup;
 500        struct dev_whitelist_item *wh;
 501
 502        if (!S_ISBLK(mode) && !S_ISCHR(mode))
 503                return 0;
 504
 505        rcu_read_lock();
 506
 507        dev_cgroup = task_devcgroup(current);
 508
 509        list_for_each_entry_rcu(wh, &dev_cgroup->whitelist, list) {
 510                if (wh->type & DEV_ALL)
 511                        goto found;
 512                if ((wh->type & DEV_BLOCK) && !S_ISBLK(mode))
 513                        continue;
 514                if ((wh->type & DEV_CHAR) && !S_ISCHR(mode))
 515                        continue;
 516                if (wh->major != ~0 && wh->major != MAJOR(dev))
 517                        continue;
 518                if (wh->minor != ~0 && wh->minor != MINOR(dev))
 519                        continue;
 520
 521                if (!(wh->access & ACC_MKNOD))
 522                        continue;
 523found:
 524                rcu_read_unlock();
 525                return 0;
 526        }
 527
 528        rcu_read_unlock();
 529
 530        return -EPERM;
 531}
 532
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