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_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 */
  76static 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
  89free_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 */
 101static 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 */
 131static 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
 146remove:
 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 */
 158static 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
 197static 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
 218static 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
 230static 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
 241static void set_majmin(char *str, unsigned m)
 242{
 243        if (m == ~0)
 244                strcpy(str, "*");
 245        else
 246                sprintf(str, "%u", m);
 247}
 248
 249static 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 */
 276static 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 */
 304static 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 */
 329static 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
 408handle:
 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
 423static 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
 435static 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
 453static 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
 460struct 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
 469int __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;
 494found:
 495                rcu_read_unlock();
 496                return 0;
 497        }
 498
 499        rcu_read_unlock();
 500
 501        return -EPERM;
 502}
 503
 504int 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;
 530found:
 531                rcu_read_unlock();
 532                return 0;
 533        }
 534
 535        rcu_read_unlock();
 536
 537        return -EPERM;
 538}
 539
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