linux/security/landlock/ruleset.c
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   1// SPDX-License-Identifier: GPL-2.0-only
   2/*
   3 * Landlock LSM - Ruleset management
   4 *
   5 * Copyright \xC2\xA9 2016-2020 Micka\xC3\xABl Sala\xC3\xBCn <mic@digikod.net>
   6 * Copyright \xC2\xA9 2018-2020 ANSSI
   7 */
   8
   9#include <linux/bits.h>
  10#include <linux/bug.h>
  11#include <linux/compiler_types.h>
  12#include <linux/err.h>
  13#include <linux/errno.h>
  14#include <linux/kernel.h>
  15#include <linux/lockdep.h>
  16#include <linux/overflow.h>
  17#include <linux/rbtree.h>
  18#include <linux/refcount.h>
  19#include <linux/slab.h>
  20#include <linux/spinlock.h>
  21#include <linux/workqueue.h>
  22
  23#include "limits.h"
  24#include "object.h"
  25#include "ruleset.h"
  26
  27static struct landlock_ruleset *create_ruleset(const u32 num_layers)
  28{
  29        struct landlock_ruleset *new_ruleset;
  30
  31        new_ruleset = kzalloc(struct_size(new_ruleset, fs_access_masks,
  32                                num_layers), GFP_KERNEL_ACCOUNT);
  33        if (!new_ruleset)
  34                return ERR_PTR(-ENOMEM);
  35        refcount_set(&new_ruleset->usage, 1);
  36        mutex_init(&new_ruleset->lock);
  37        new_ruleset->root = RB_ROOT;
  38        new_ruleset->num_layers = num_layers;
  39        /*
  40         * hierarchy = NULL
  41         * num_rules = 0
  42         * fs_access_masks[] = 0
  43         */
  44        return new_ruleset;
  45}
  46
  47struct landlock_ruleset *landlock_create_ruleset(const u32 fs_access_mask)
  48{
  49        struct landlock_ruleset *new_ruleset;
  50
  51        /* Informs about useless ruleset. */
  52        if (!fs_access_mask)
  53                return ERR_PTR(-ENOMSG);
  54        new_ruleset = create_ruleset(1);
  55        if (!IS_ERR(new_ruleset))
  56                new_ruleset->fs_access_masks[0] = fs_access_mask;
  57        return new_ruleset;
  58}
  59
  60static void build_check_rule(void)
  61{
  62        const struct landlock_rule rule = {
  63                .num_layers = ~0,
  64        };
  65
  66        BUILD_BUG_ON(rule.num_layers < LANDLOCK_MAX_NUM_LAYERS);
  67}
  68
  69static struct landlock_rule *create_rule(
  70                struct landlock_object *const object,
  71                const struct landlock_layer (*const layers)[],
  72                const u32 num_layers,
  73                const struct landlock_layer *const new_layer)
  74{
  75        struct landlock_rule *new_rule;
  76        u32 new_num_layers;
  77
  78        build_check_rule();
  79        if (new_layer) {
  80                /* Should already be checked by landlock_merge_ruleset(). */
  81                if (WARN_ON_ONCE(num_layers >= LANDLOCK_MAX_NUM_LAYERS))
  82                        return ERR_PTR(-E2BIG);
  83                new_num_layers = num_layers + 1;
  84        } else {
  85                new_num_layers = num_layers;
  86        }
  87        new_rule = kzalloc(struct_size(new_rule, layers, new_num_layers),
  88                        GFP_KERNEL_ACCOUNT);
  89        if (!new_rule)
  90                return ERR_PTR(-ENOMEM);
  91        RB_CLEAR_NODE(&new_rule->node);
  92        landlock_get_object(object);
  93        new_rule->object = object;
  94        new_rule->num_layers = new_num_layers;
  95        /* Copies the original layer stack. */
  96        memcpy(new_rule->layers, layers,
  97                        flex_array_size(new_rule, layers, num_layers));
  98        if (new_layer)
  99                /* Adds a copy of @new_layer on the layer stack. */
 100                new_rule->layers[new_rule->num_layers - 1] = *new_layer;
 101        return new_rule;
 102}
 103
 104static void free_rule(struct landlock_rule *const rule)
 105{
 106        might_sleep();
 107        if (!rule)
 108                return;
 109        landlock_put_object(rule->object);
 110        kfree(rule);
 111}
 112
 113static void build_check_ruleset(void)
 114{
 115        const struct landlock_ruleset ruleset = {
 116                .num_rules = ~0,
 117                .num_layers = ~0,
 118        };
 119        typeof(ruleset.fs_access_masks[0]) fs_access_mask = ~0;
 120
 121        BUILD_BUG_ON(ruleset.num_rules < LANDLOCK_MAX_NUM_RULES);
 122        BUILD_BUG_ON(ruleset.num_layers < LANDLOCK_MAX_NUM_LAYERS);
 123        BUILD_BUG_ON(fs_access_mask < LANDLOCK_MASK_ACCESS_FS);
 124}
 125
 126/**
 127 * insert_rule - Create and insert a rule in a ruleset
 128 *
 129 * @ruleset: The ruleset to be updated.
 130 * @object: The object to build the new rule with.  The underlying kernel
 131 *          object must be held by the caller.
 132 * @layers: One or multiple layers to be copied into the new rule.
 133 * @num_layers: The number of @layers entries.
 134 *
 135 * When user space requests to add a new rule to a ruleset, @layers only
 136 * contains one entry and this entry is not assigned to any level.  In this
 137 * case, the new rule will extend @ruleset, similarly to a boolean OR between
 138 * access rights.
 139 *
 140 * When merging a ruleset in a domain, or copying a domain, @layers will be
 141 * added to @ruleset as new constraints, similarly to a boolean AND between
 142 * access rights.
 143 */
 144static int insert_rule(struct landlock_ruleset *const ruleset,
 145                struct landlock_object *const object,
 146                const struct landlock_layer (*const layers)[],
 147                size_t num_layers)
 148{
 149        struct rb_node **walker_node;
 150        struct rb_node *parent_node = NULL;
 151        struct landlock_rule *new_rule;
 152
 153        might_sleep();
 154        lockdep_assert_held(&ruleset->lock);
 155        if (WARN_ON_ONCE(!object || !layers))
 156                return -ENOENT;
 157        walker_node = &(ruleset->root.rb_node);
 158        while (*walker_node) {
 159                struct landlock_rule *const this = rb_entry(*walker_node,
 160                                struct landlock_rule, node);
 161
 162                if (this->object != object) {
 163                        parent_node = *walker_node;
 164                        if (this->object < object)
 165                                walker_node = &((*walker_node)->rb_right);
 166                        else
 167                                walker_node = &((*walker_node)->rb_left);
 168                        continue;
 169                }
 170
 171                /* Only a single-level layer should match an existing rule. */
 172                if (WARN_ON_ONCE(num_layers != 1))
 173                        return -EINVAL;
 174
 175                /* If there is a matching rule, updates it. */
 176                if ((*layers)[0].level == 0) {
 177                        /*
 178                         * Extends access rights when the request comes from
 179                         * landlock_add_rule(2), i.e. @ruleset is not a domain.
 180                         */
 181                        if (WARN_ON_ONCE(this->num_layers != 1))
 182                                return -EINVAL;
 183                        if (WARN_ON_ONCE(this->layers[0].level != 0))
 184                                return -EINVAL;
 185                        this->layers[0].access |= (*layers)[0].access;
 186                        return 0;
 187                }
 188
 189                if (WARN_ON_ONCE(this->layers[0].level == 0))
 190                        return -EINVAL;
 191
 192                /*
 193                 * Intersects access rights when it is a merge between a
 194                 * ruleset and a domain.
 195                 */
 196                new_rule = create_rule(object, &this->layers, this->num_layers,
 197                                &(*layers)[0]);
 198                if (IS_ERR(new_rule))
 199                        return PTR_ERR(new_rule);
 200                rb_replace_node(&this->node, &new_rule->node, &ruleset->root);
 201                free_rule(this);
 202                return 0;
 203        }
 204
 205        /* There is no match for @object. */
 206        build_check_ruleset();
 207        if (ruleset->num_rules >= LANDLOCK_MAX_NUM_RULES)
 208                return -E2BIG;
 209        new_rule = create_rule(object, layers, num_layers, NULL);
 210        if (IS_ERR(new_rule))
 211                return PTR_ERR(new_rule);
 212        rb_link_node(&new_rule->node, parent_node, walker_node);
 213        rb_insert_color(&new_rule->node, &ruleset->root);
 214        ruleset->num_rules++;
 215        return 0;
 216}
 217
 218static void build_check_layer(void)
 219{
 220        const struct landlock_layer layer = {
 221                .level = ~0,
 222                .access = ~0,
 223        };
 224
 225        BUILD_BUG_ON(layer.level < LANDLOCK_MAX_NUM_LAYERS);
 226        BUILD_BUG_ON(layer.access < LANDLOCK_MASK_ACCESS_FS);
 227}
 228
 229/* @ruleset must be locked by the caller. */
 230int landlock_insert_rule(struct landlock_ruleset *const ruleset,
 231                struct landlock_object *const object, const u32 access)
 232{
 233        struct landlock_layer layers[] = {{
 234                .access = access,
 235                /* When @level is zero, insert_rule() extends @ruleset. */
 236                .level = 0,
 237        }};
 238
 239        build_check_layer();
 240        return insert_rule(ruleset, object, &layers, ARRAY_SIZE(layers));
 241}
 242
 243static inline void get_hierarchy(struct landlock_hierarchy *const hierarchy)
 244{
 245        if (hierarchy)
 246                refcount_inc(&hierarchy->usage);
 247}
 248
 249static void put_hierarchy(struct landlock_hierarchy *hierarchy)
 250{
 251        while (hierarchy && refcount_dec_and_test(&hierarchy->usage)) {
 252                const struct landlock_hierarchy *const freeme = hierarchy;
 253
 254                hierarchy = hierarchy->parent;
 255                kfree(freeme);
 256        }
 257}
 258
 259static int merge_ruleset(struct landlock_ruleset *const dst,
 260                struct landlock_ruleset *const src)
 261{
 262        struct landlock_rule *walker_rule, *next_rule;
 263        int err = 0;
 264
 265        might_sleep();
 266        /* Should already be checked by landlock_merge_ruleset() */
 267        if (WARN_ON_ONCE(!src))
 268                return 0;
 269        /* Only merge into a domain. */
 270        if (WARN_ON_ONCE(!dst || !dst->hierarchy))
 271                return -EINVAL;
 272
 273        /* Locks @dst first because we are its only owner. */
 274        mutex_lock(&dst->lock);
 275        mutex_lock_nested(&src->lock, SINGLE_DEPTH_NESTING);
 276
 277        /* Stacks the new layer. */
 278        if (WARN_ON_ONCE(src->num_layers != 1 || dst->num_layers < 1)) {
 279                err = -EINVAL;
 280                goto out_unlock;
 281        }
 282        dst->fs_access_masks[dst->num_layers - 1] = src->fs_access_masks[0];
 283
 284        /* Merges the @src tree. */
 285        rbtree_postorder_for_each_entry_safe(walker_rule, next_rule,
 286                        &src->root, node) {
 287                struct landlock_layer layers[] = {{
 288                        .level = dst->num_layers,
 289                }};
 290
 291                if (WARN_ON_ONCE(walker_rule->num_layers != 1)) {
 292                        err = -EINVAL;
 293                        goto out_unlock;
 294                }
 295                if (WARN_ON_ONCE(walker_rule->layers[0].level != 0)) {
 296                        err = -EINVAL;
 297                        goto out_unlock;
 298                }
 299                layers[0].access = walker_rule->layers[0].access;
 300                err = insert_rule(dst, walker_rule->object, &layers,
 301                                ARRAY_SIZE(layers));
 302                if (err)
 303                        goto out_unlock;
 304        }
 305
 306out_unlock:
 307        mutex_unlock(&src->lock);
 308        mutex_unlock(&dst->lock);
 309        return err;
 310}
 311
 312static int inherit_ruleset(struct landlock_ruleset *const parent,
 313                struct landlock_ruleset *const child)
 314{
 315        struct landlock_rule *walker_rule, *next_rule;
 316        int err = 0;
 317
 318        might_sleep();
 319        if (!parent)
 320                return 0;
 321
 322        /* Locks @child first because we are its only owner. */
 323        mutex_lock(&child->lock);
 324        mutex_lock_nested(&parent->lock, SINGLE_DEPTH_NESTING);
 325
 326        /* Copies the @parent tree. */
 327        rbtree_postorder_for_each_entry_safe(walker_rule, next_rule,
 328                        &parent->root, node) {
 329                err = insert_rule(child, walker_rule->object,
 330                                &walker_rule->layers, walker_rule->num_layers);
 331                if (err)
 332                        goto out_unlock;
 333        }
 334
 335        if (WARN_ON_ONCE(child->num_layers <= parent->num_layers)) {
 336                err = -EINVAL;
 337                goto out_unlock;
 338        }
 339        /* Copies the parent layer stack and leaves a space for the new layer. */
 340        memcpy(child->fs_access_masks, parent->fs_access_masks,
 341                        flex_array_size(parent, fs_access_masks, parent->num_layers));
 342
 343        if (WARN_ON_ONCE(!parent->hierarchy)) {
 344                err = -EINVAL;
 345                goto out_unlock;
 346        }
 347        get_hierarchy(parent->hierarchy);
 348        child->hierarchy->parent = parent->hierarchy;
 349
 350out_unlock:
 351        mutex_unlock(&parent->lock);
 352        mutex_unlock(&child->lock);
 353        return err;
 354}
 355
 356static void free_ruleset(struct landlock_ruleset *const ruleset)
 357{
 358        struct landlock_rule *freeme, *next;
 359
 360        might_sleep();
 361        rbtree_postorder_for_each_entry_safe(freeme, next, &ruleset->root,
 362                        node)
 363                free_rule(freeme);
 364        put_hierarchy(ruleset->hierarchy);
 365        kfree(ruleset);
 366}
 367
 368void landlock_put_ruleset(struct landlock_ruleset *const ruleset)
 369{
 370        might_sleep();
 371        if (ruleset && refcount_dec_and_test(&ruleset->usage))
 372                free_ruleset(ruleset);
 373}
 374
 375static void free_ruleset_work(struct work_struct *const work)
 376{
 377        struct landlock_ruleset *ruleset;
 378
 379        ruleset = container_of(work, struct landlock_ruleset, work_free);
 380        free_ruleset(ruleset);
 381}
 382
 383void landlock_put_ruleset_deferred(struct landlock_ruleset *const ruleset)
 384{
 385        if (ruleset && refcount_dec_and_test(&ruleset->usage)) {
 386                INIT_WORK(&ruleset->work_free, free_ruleset_work);
 387                schedule_work(&ruleset->work_free);
 388        }
 389}
 390
 391/**
 392 * landlock_merge_ruleset - Merge a ruleset with a domain
 393 *
 394 * @parent: Parent domain.
 395 * @ruleset: New ruleset to be merged.
 396 *
 397 * Returns the intersection of @parent and @ruleset, or returns @parent if
 398 * @ruleset is empty, or returns a duplicate of @ruleset if @parent is empty.
 399 */
 400struct landlock_ruleset *landlock_merge_ruleset(
 401                struct landlock_ruleset *const parent,
 402                struct landlock_ruleset *const ruleset)
 403{
 404        struct landlock_ruleset *new_dom;
 405        u32 num_layers;
 406        int err;
 407
 408        might_sleep();
 409        if (WARN_ON_ONCE(!ruleset || parent == ruleset))
 410                return ERR_PTR(-EINVAL);
 411
 412        if (parent) {
 413                if (parent->num_layers >= LANDLOCK_MAX_NUM_LAYERS)
 414                        return ERR_PTR(-E2BIG);
 415                num_layers = parent->num_layers + 1;
 416        } else {
 417                num_layers = 1;
 418        }
 419
 420        /* Creates a new domain... */
 421        new_dom = create_ruleset(num_layers);
 422        if (IS_ERR(new_dom))
 423                return new_dom;
 424        new_dom->hierarchy = kzalloc(sizeof(*new_dom->hierarchy),
 425                        GFP_KERNEL_ACCOUNT);
 426        if (!new_dom->hierarchy) {
 427                err = -ENOMEM;
 428                goto out_put_dom;
 429        }
 430        refcount_set(&new_dom->hierarchy->usage, 1);
 431
 432        /* ...as a child of @parent... */
 433        err = inherit_ruleset(parent, new_dom);
 434        if (err)
 435                goto out_put_dom;
 436
 437        /* ...and including @ruleset. */
 438        err = merge_ruleset(new_dom, ruleset);
 439        if (err)
 440                goto out_put_dom;
 441
 442        return new_dom;
 443
 444out_put_dom:
 445        landlock_put_ruleset(new_dom);
 446        return ERR_PTR(err);
 447}
 448
 449/*
 450 * The returned access has the same lifetime as @ruleset.
 451 */
 452const struct landlock_rule *landlock_find_rule(
 453                const struct landlock_ruleset *const ruleset,
 454                const struct landlock_object *const object)
 455{
 456        const struct rb_node *node;
 457
 458        if (!object)
 459                return NULL;
 460        node = ruleset->root.rb_node;
 461        while (node) {
 462                struct landlock_rule *this = rb_entry(node,
 463                                struct landlock_rule, node);
 464
 465                if (this->object == object)
 466                        return this;
 467                if (this->object < object)
 468                        node = node->rb_right;
 469                else
 470                        node = node->rb_left;
 471        }
 472        return NULL;
 473}
 474