1 // SPDX-License-Identifier: GPL-2.0-only
3 * Landlock LSM - Ruleset management
5 * Copyright © 2016-2020 Mickaël Salaün <mic@digikod.net>
6 * Copyright © 2018-2020 ANSSI
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>
27 static struct landlock_ruleset *create_ruleset(const u32 num_layers)
29 struct landlock_ruleset *new_ruleset;
32 kzalloc(struct_size(new_ruleset, access_masks, num_layers),
35 return ERR_PTR(-ENOMEM);
36 refcount_set(&new_ruleset->usage, 1);
37 mutex_init(&new_ruleset->lock);
38 new_ruleset->root_inode = RB_ROOT;
40 #if IS_ENABLED(CONFIG_INET)
41 new_ruleset->root_net_port = RB_ROOT;
42 #endif /* IS_ENABLED(CONFIG_INET) */
44 new_ruleset->num_layers = num_layers;
53 struct landlock_ruleset *
54 landlock_create_ruleset(const access_mask_t fs_access_mask,
55 const access_mask_t net_access_mask)
57 struct landlock_ruleset *new_ruleset;
59 /* Informs about useless ruleset. */
60 if (!fs_access_mask && !net_access_mask)
61 return ERR_PTR(-ENOMSG);
62 new_ruleset = create_ruleset(1);
63 if (IS_ERR(new_ruleset))
66 landlock_add_fs_access_mask(new_ruleset, fs_access_mask, 0);
68 landlock_add_net_access_mask(new_ruleset, net_access_mask, 0);
72 static void build_check_rule(void)
74 const struct landlock_rule rule = {
78 BUILD_BUG_ON(rule.num_layers < LANDLOCK_MAX_NUM_LAYERS);
81 static bool is_object_pointer(const enum landlock_key_type key_type)
84 case LANDLOCK_KEY_INODE:
87 #if IS_ENABLED(CONFIG_INET)
88 case LANDLOCK_KEY_NET_PORT:
90 #endif /* IS_ENABLED(CONFIG_INET) */
98 static struct landlock_rule *
99 create_rule(const struct landlock_id id,
100 const struct landlock_layer (*const layers)[], const u32 num_layers,
101 const struct landlock_layer *const new_layer)
103 struct landlock_rule *new_rule;
108 /* Should already be checked by landlock_merge_ruleset(). */
109 if (WARN_ON_ONCE(num_layers >= LANDLOCK_MAX_NUM_LAYERS))
110 return ERR_PTR(-E2BIG);
111 new_num_layers = num_layers + 1;
113 new_num_layers = num_layers;
115 new_rule = kzalloc(struct_size(new_rule, layers, new_num_layers),
118 return ERR_PTR(-ENOMEM);
119 RB_CLEAR_NODE(&new_rule->node);
120 if (is_object_pointer(id.type)) {
121 /* This should be catched by insert_rule(). */
122 WARN_ON_ONCE(!id.key.object);
123 landlock_get_object(id.key.object);
126 new_rule->key = id.key;
127 new_rule->num_layers = new_num_layers;
128 /* Copies the original layer stack. */
129 memcpy(new_rule->layers, layers,
130 flex_array_size(new_rule, layers, num_layers));
132 /* Adds a copy of @new_layer on the layer stack. */
133 new_rule->layers[new_rule->num_layers - 1] = *new_layer;
137 static struct rb_root *get_root(struct landlock_ruleset *const ruleset,
138 const enum landlock_key_type key_type)
141 case LANDLOCK_KEY_INODE:
142 return &ruleset->root_inode;
144 #if IS_ENABLED(CONFIG_INET)
145 case LANDLOCK_KEY_NET_PORT:
146 return &ruleset->root_net_port;
147 #endif /* IS_ENABLED(CONFIG_INET) */
151 return ERR_PTR(-EINVAL);
155 static void free_rule(struct landlock_rule *const rule,
156 const enum landlock_key_type key_type)
161 if (is_object_pointer(key_type))
162 landlock_put_object(rule->key.object);
166 static void build_check_ruleset(void)
168 const struct landlock_ruleset ruleset = {
172 typeof(ruleset.access_masks[0]) access_masks = ~0;
174 BUILD_BUG_ON(ruleset.num_rules < LANDLOCK_MAX_NUM_RULES);
175 BUILD_BUG_ON(ruleset.num_layers < LANDLOCK_MAX_NUM_LAYERS);
176 BUILD_BUG_ON(access_masks <
177 ((LANDLOCK_MASK_ACCESS_FS << LANDLOCK_SHIFT_ACCESS_FS) |
178 (LANDLOCK_MASK_ACCESS_NET << LANDLOCK_SHIFT_ACCESS_NET)));
182 * insert_rule - Create and insert a rule in a ruleset
184 * @ruleset: The ruleset to be updated.
185 * @id: The ID to build the new rule with. The underlying kernel object, if
186 * any, must be held by the caller.
187 * @layers: One or multiple layers to be copied into the new rule.
188 * @num_layers: The number of @layers entries.
190 * When user space requests to add a new rule to a ruleset, @layers only
191 * contains one entry and this entry is not assigned to any level. In this
192 * case, the new rule will extend @ruleset, similarly to a boolean OR between
195 * When merging a ruleset in a domain, or copying a domain, @layers will be
196 * added to @ruleset as new constraints, similarly to a boolean AND between
199 static int insert_rule(struct landlock_ruleset *const ruleset,
200 const struct landlock_id id,
201 const struct landlock_layer (*const layers)[],
202 const size_t num_layers)
204 struct rb_node **walker_node;
205 struct rb_node *parent_node = NULL;
206 struct landlock_rule *new_rule;
207 struct rb_root *root;
210 lockdep_assert_held(&ruleset->lock);
211 if (WARN_ON_ONCE(!layers))
214 if (is_object_pointer(id.type) && WARN_ON_ONCE(!id.key.object))
217 root = get_root(ruleset, id.type);
219 return PTR_ERR(root);
221 walker_node = &root->rb_node;
222 while (*walker_node) {
223 struct landlock_rule *const this =
224 rb_entry(*walker_node, struct landlock_rule, node);
226 if (this->key.data != id.key.data) {
227 parent_node = *walker_node;
228 if (this->key.data < id.key.data)
229 walker_node = &((*walker_node)->rb_right);
231 walker_node = &((*walker_node)->rb_left);
235 /* Only a single-level layer should match an existing rule. */
236 if (WARN_ON_ONCE(num_layers != 1))
239 /* If there is a matching rule, updates it. */
240 if ((*layers)[0].level == 0) {
242 * Extends access rights when the request comes from
243 * landlock_add_rule(2), i.e. @ruleset is not a domain.
245 if (WARN_ON_ONCE(this->num_layers != 1))
247 if (WARN_ON_ONCE(this->layers[0].level != 0))
249 this->layers[0].access |= (*layers)[0].access;
253 if (WARN_ON_ONCE(this->layers[0].level == 0))
257 * Intersects access rights when it is a merge between a
258 * ruleset and a domain.
260 new_rule = create_rule(id, &this->layers, this->num_layers,
262 if (IS_ERR(new_rule))
263 return PTR_ERR(new_rule);
264 rb_replace_node(&this->node, &new_rule->node, root);
265 free_rule(this, id.type);
269 /* There is no match for @id. */
270 build_check_ruleset();
271 if (ruleset->num_rules >= LANDLOCK_MAX_NUM_RULES)
273 new_rule = create_rule(id, layers, num_layers, NULL);
274 if (IS_ERR(new_rule))
275 return PTR_ERR(new_rule);
276 rb_link_node(&new_rule->node, parent_node, walker_node);
277 rb_insert_color(&new_rule->node, root);
278 ruleset->num_rules++;
282 static void build_check_layer(void)
284 const struct landlock_layer layer = {
289 BUILD_BUG_ON(layer.level < LANDLOCK_MAX_NUM_LAYERS);
290 BUILD_BUG_ON(layer.access < LANDLOCK_MASK_ACCESS_FS);
293 /* @ruleset must be locked by the caller. */
294 int landlock_insert_rule(struct landlock_ruleset *const ruleset,
295 const struct landlock_id id,
296 const access_mask_t access)
298 struct landlock_layer layers[] = { {
300 /* When @level is zero, insert_rule() extends @ruleset. */
305 return insert_rule(ruleset, id, &layers, ARRAY_SIZE(layers));
308 static void get_hierarchy(struct landlock_hierarchy *const hierarchy)
311 refcount_inc(&hierarchy->usage);
314 static void put_hierarchy(struct landlock_hierarchy *hierarchy)
316 while (hierarchy && refcount_dec_and_test(&hierarchy->usage)) {
317 const struct landlock_hierarchy *const freeme = hierarchy;
319 hierarchy = hierarchy->parent;
324 static int merge_tree(struct landlock_ruleset *const dst,
325 struct landlock_ruleset *const src,
326 const enum landlock_key_type key_type)
328 struct landlock_rule *walker_rule, *next_rule;
329 struct rb_root *src_root;
333 lockdep_assert_held(&dst->lock);
334 lockdep_assert_held(&src->lock);
336 src_root = get_root(src, key_type);
337 if (IS_ERR(src_root))
338 return PTR_ERR(src_root);
340 /* Merges the @src tree. */
341 rbtree_postorder_for_each_entry_safe(walker_rule, next_rule, src_root,
343 struct landlock_layer layers[] = { {
344 .level = dst->num_layers,
346 const struct landlock_id id = {
347 .key = walker_rule->key,
351 if (WARN_ON_ONCE(walker_rule->num_layers != 1))
354 if (WARN_ON_ONCE(walker_rule->layers[0].level != 0))
357 layers[0].access = walker_rule->layers[0].access;
359 err = insert_rule(dst, id, &layers, ARRAY_SIZE(layers));
366 static int merge_ruleset(struct landlock_ruleset *const dst,
367 struct landlock_ruleset *const src)
372 /* Should already be checked by landlock_merge_ruleset() */
373 if (WARN_ON_ONCE(!src))
375 /* Only merge into a domain. */
376 if (WARN_ON_ONCE(!dst || !dst->hierarchy))
379 /* Locks @dst first because we are its only owner. */
380 mutex_lock(&dst->lock);
381 mutex_lock_nested(&src->lock, SINGLE_DEPTH_NESTING);
383 /* Stacks the new layer. */
384 if (WARN_ON_ONCE(src->num_layers != 1 || dst->num_layers < 1)) {
388 dst->access_masks[dst->num_layers - 1] = src->access_masks[0];
390 /* Merges the @src inode tree. */
391 err = merge_tree(dst, src, LANDLOCK_KEY_INODE);
395 #if IS_ENABLED(CONFIG_INET)
396 /* Merges the @src network port tree. */
397 err = merge_tree(dst, src, LANDLOCK_KEY_NET_PORT);
400 #endif /* IS_ENABLED(CONFIG_INET) */
403 mutex_unlock(&src->lock);
404 mutex_unlock(&dst->lock);
408 static int inherit_tree(struct landlock_ruleset *const parent,
409 struct landlock_ruleset *const child,
410 const enum landlock_key_type key_type)
412 struct landlock_rule *walker_rule, *next_rule;
413 struct rb_root *parent_root;
417 lockdep_assert_held(&parent->lock);
418 lockdep_assert_held(&child->lock);
420 parent_root = get_root(parent, key_type);
421 if (IS_ERR(parent_root))
422 return PTR_ERR(parent_root);
424 /* Copies the @parent inode or network tree. */
425 rbtree_postorder_for_each_entry_safe(walker_rule, next_rule,
427 const struct landlock_id id = {
428 .key = walker_rule->key,
432 err = insert_rule(child, id, &walker_rule->layers,
433 walker_rule->num_layers);
440 static int inherit_ruleset(struct landlock_ruleset *const parent,
441 struct landlock_ruleset *const child)
449 /* Locks @child first because we are its only owner. */
450 mutex_lock(&child->lock);
451 mutex_lock_nested(&parent->lock, SINGLE_DEPTH_NESTING);
453 /* Copies the @parent inode tree. */
454 err = inherit_tree(parent, child, LANDLOCK_KEY_INODE);
458 #if IS_ENABLED(CONFIG_INET)
459 /* Copies the @parent network port tree. */
460 err = inherit_tree(parent, child, LANDLOCK_KEY_NET_PORT);
463 #endif /* IS_ENABLED(CONFIG_INET) */
465 if (WARN_ON_ONCE(child->num_layers <= parent->num_layers)) {
469 /* Copies the parent layer stack and leaves a space for the new layer. */
470 memcpy(child->access_masks, parent->access_masks,
471 flex_array_size(parent, access_masks, parent->num_layers));
473 if (WARN_ON_ONCE(!parent->hierarchy)) {
477 get_hierarchy(parent->hierarchy);
478 child->hierarchy->parent = parent->hierarchy;
481 mutex_unlock(&parent->lock);
482 mutex_unlock(&child->lock);
486 static void free_ruleset(struct landlock_ruleset *const ruleset)
488 struct landlock_rule *freeme, *next;
491 rbtree_postorder_for_each_entry_safe(freeme, next, &ruleset->root_inode,
493 free_rule(freeme, LANDLOCK_KEY_INODE);
495 #if IS_ENABLED(CONFIG_INET)
496 rbtree_postorder_for_each_entry_safe(freeme, next,
497 &ruleset->root_net_port, node)
498 free_rule(freeme, LANDLOCK_KEY_NET_PORT);
499 #endif /* IS_ENABLED(CONFIG_INET) */
501 put_hierarchy(ruleset->hierarchy);
505 void landlock_put_ruleset(struct landlock_ruleset *const ruleset)
508 if (ruleset && refcount_dec_and_test(&ruleset->usage))
509 free_ruleset(ruleset);
512 static void free_ruleset_work(struct work_struct *const work)
514 struct landlock_ruleset *ruleset;
516 ruleset = container_of(work, struct landlock_ruleset, work_free);
517 free_ruleset(ruleset);
520 void landlock_put_ruleset_deferred(struct landlock_ruleset *const ruleset)
522 if (ruleset && refcount_dec_and_test(&ruleset->usage)) {
523 INIT_WORK(&ruleset->work_free, free_ruleset_work);
524 schedule_work(&ruleset->work_free);
529 * landlock_merge_ruleset - Merge a ruleset with a domain
531 * @parent: Parent domain.
532 * @ruleset: New ruleset to be merged.
534 * Returns the intersection of @parent and @ruleset, or returns @parent if
535 * @ruleset is empty, or returns a duplicate of @ruleset if @parent is empty.
537 struct landlock_ruleset *
538 landlock_merge_ruleset(struct landlock_ruleset *const parent,
539 struct landlock_ruleset *const ruleset)
541 struct landlock_ruleset *new_dom;
546 if (WARN_ON_ONCE(!ruleset || parent == ruleset))
547 return ERR_PTR(-EINVAL);
550 if (parent->num_layers >= LANDLOCK_MAX_NUM_LAYERS)
551 return ERR_PTR(-E2BIG);
552 num_layers = parent->num_layers + 1;
557 /* Creates a new domain... */
558 new_dom = create_ruleset(num_layers);
562 kzalloc(sizeof(*new_dom->hierarchy), GFP_KERNEL_ACCOUNT);
563 if (!new_dom->hierarchy) {
567 refcount_set(&new_dom->hierarchy->usage, 1);
569 /* ...as a child of @parent... */
570 err = inherit_ruleset(parent, new_dom);
574 /* ...and including @ruleset. */
575 err = merge_ruleset(new_dom, ruleset);
582 landlock_put_ruleset(new_dom);
587 * The returned access has the same lifetime as @ruleset.
589 const struct landlock_rule *
590 landlock_find_rule(const struct landlock_ruleset *const ruleset,
591 const struct landlock_id id)
593 const struct rb_root *root;
594 const struct rb_node *node;
596 root = get_root((struct landlock_ruleset *)ruleset, id.type);
599 node = root->rb_node;
602 struct landlock_rule *this =
603 rb_entry(node, struct landlock_rule, node);
605 if (this->key.data == id.key.data)
607 if (this->key.data < id.key.data)
608 node = node->rb_right;
610 node = node->rb_left;
616 * @layer_masks is read and may be updated according to the access request and
618 * @masks_array_size must be equal to ARRAY_SIZE(*layer_masks).
620 * Returns true if the request is allowed (i.e. relevant layer masks for the
621 * request are empty).
623 bool landlock_unmask_layers(const struct landlock_rule *const rule,
624 const access_mask_t access_request,
625 layer_mask_t (*const layer_masks)[],
626 const size_t masks_array_size)
630 if (!access_request || !layer_masks)
636 * An access is granted if, for each policy layer, at least one rule
637 * encountered on the pathwalk grants the requested access,
638 * regardless of its position in the layer stack. We must then check
639 * the remaining layers for each inode, from the first added layer to
640 * the last one. When there is multiple requested accesses, for each
641 * policy layer, the full set of requested accesses may not be granted
642 * by only one rule, but by the union (binary OR) of multiple rules.
643 * E.g. /a/b <execute> + /a <read> => /a/b <execute + read>
645 for (layer_level = 0; layer_level < rule->num_layers; layer_level++) {
646 const struct landlock_layer *const layer =
647 &rule->layers[layer_level];
648 const layer_mask_t layer_bit = BIT_ULL(layer->level - 1);
649 const unsigned long access_req = access_request;
650 unsigned long access_bit;
654 * Records in @layer_masks which layer grants access to each
658 for_each_set_bit(access_bit, &access_req, masks_array_size) {
659 if (layer->access & BIT_ULL(access_bit))
660 (*layer_masks)[access_bit] &= ~layer_bit;
661 is_empty = is_empty && !(*layer_masks)[access_bit];
669 typedef access_mask_t
670 get_access_mask_t(const struct landlock_ruleset *const ruleset,
671 const u16 layer_level);
674 * landlock_init_layer_masks - Initialize layer masks from an access request
676 * Populates @layer_masks such that for each access right in @access_request,
677 * the bits for all the layers are set where this access right is handled.
679 * @domain: The domain that defines the current restrictions.
680 * @access_request: The requested access rights to check.
681 * @layer_masks: It must contain %LANDLOCK_NUM_ACCESS_FS or
682 * %LANDLOCK_NUM_ACCESS_NET elements according to @key_type.
683 * @key_type: The key type to switch between access masks of different types.
685 * Returns: An access mask where each access right bit is set which is handled
686 * in any of the active layers in @domain.
689 landlock_init_layer_masks(const struct landlock_ruleset *const domain,
690 const access_mask_t access_request,
691 layer_mask_t (*const layer_masks)[],
692 const enum landlock_key_type key_type)
694 access_mask_t handled_accesses = 0;
695 size_t layer_level, num_access;
696 get_access_mask_t *get_access_mask;
699 case LANDLOCK_KEY_INODE:
700 get_access_mask = landlock_get_fs_access_mask;
701 num_access = LANDLOCK_NUM_ACCESS_FS;
704 #if IS_ENABLED(CONFIG_INET)
705 case LANDLOCK_KEY_NET_PORT:
706 get_access_mask = landlock_get_net_access_mask;
707 num_access = LANDLOCK_NUM_ACCESS_NET;
709 #endif /* IS_ENABLED(CONFIG_INET) */
716 memset(layer_masks, 0,
717 array_size(sizeof((*layer_masks)[0]), num_access));
719 /* An empty access request can happen because of O_WRONLY | O_RDWR. */
723 /* Saves all handled accesses per layer. */
724 for (layer_level = 0; layer_level < domain->num_layers; layer_level++) {
725 const unsigned long access_req = access_request;
726 const access_mask_t access_mask =
727 get_access_mask(domain, layer_level);
728 unsigned long access_bit;
730 for_each_set_bit(access_bit, &access_req, num_access) {
731 if (BIT_ULL(access_bit) & access_mask) {
732 (*layer_masks)[access_bit] |=
733 BIT_ULL(layer_level);
734 handled_accesses |= BIT_ULL(access_bit);
738 return handled_accesses;