1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Landlock LSM - Ruleset management
4 *
5 * Copyright © 2016-2020 Mickaël Salaün <mic@digikod.net>
6 * Copyright © 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 =
32		kzalloc(struct_size(new_ruleset, fs_access_masks, num_layers),
33			GFP_KERNEL_ACCOUNT);
34	if (!new_ruleset)
35		return ERR_PTR(-ENOMEM);
36	refcount_set(&new_ruleset->usage, 1);
37	mutex_init(&new_ruleset->lock);
38	new_ruleset->root = RB_ROOT;
39	new_ruleset->num_layers = num_layers;
40	/*
41	 * hierarchy = NULL
42	 * num_rules = 0
43	 * fs_access_masks[] = 0
44	 */
45	return new_ruleset;
46}
47
48struct landlock_ruleset *
49landlock_create_ruleset(const access_mask_t fs_access_mask)
50{
51	struct landlock_ruleset *new_ruleset;
52
53	/* Informs about useless ruleset. */
54	if (!fs_access_mask)
55		return ERR_PTR(-ENOMSG);
56	new_ruleset = create_ruleset(1);
57	if (!IS_ERR(new_ruleset))
58		new_ruleset->fs_access_masks[0] = fs_access_mask;
59	return new_ruleset;
60}
61
62static void build_check_rule(void)
63{
64	const struct landlock_rule rule = {
65		.num_layers = ~0,
66	};
67
68	BUILD_BUG_ON(rule.num_layers < LANDLOCK_MAX_NUM_LAYERS);
69}
70
71static struct landlock_rule *
72create_rule(struct landlock_object *const object,
73	    const struct landlock_layer (*const layers)[], const u32 num_layers,
74	    const struct landlock_layer *const new_layer)
75{
76	struct landlock_rule *new_rule;
77	u32 new_num_layers;
78
79	build_check_rule();
80	if (new_layer) {
81		/* Should already be checked by landlock_merge_ruleset(). */
82		if (WARN_ON_ONCE(num_layers >= LANDLOCK_MAX_NUM_LAYERS))
83			return ERR_PTR(-E2BIG);
84		new_num_layers = num_layers + 1;
85	} else {
86		new_num_layers = num_layers;
87	}
88	new_rule = kzalloc(struct_size(new_rule, layers, new_num_layers),
89			   GFP_KERNEL_ACCOUNT);
90	if (!new_rule)
91		return ERR_PTR(-ENOMEM);
92	RB_CLEAR_NODE(&new_rule->node);
93	landlock_get_object(object);
94	new_rule->object = object;
95	new_rule->num_layers = new_num_layers;
96	/* Copies the original layer stack. */
97	memcpy(new_rule->layers, layers,
98	       flex_array_size(new_rule, layers, num_layers));
99	if (new_layer)
100		/* Adds a copy of @new_layer on the layer stack. */
101		new_rule->layers[new_rule->num_layers - 1] = *new_layer;
102	return new_rule;
103}
104
105static void free_rule(struct landlock_rule *const rule)
106{
107	might_sleep();
108	if (!rule)
109		return;
110	landlock_put_object(rule->object);
111	kfree(rule);
112}
113
114static void build_check_ruleset(void)
115{
116	const struct landlock_ruleset ruleset = {
117		.num_rules = ~0,
118		.num_layers = ~0,
119	};
120	typeof(ruleset.fs_access_masks[0]) fs_access_mask = ~0;
121
122	BUILD_BUG_ON(ruleset.num_rules < LANDLOCK_MAX_NUM_RULES);
123	BUILD_BUG_ON(ruleset.num_layers < LANDLOCK_MAX_NUM_LAYERS);
124	BUILD_BUG_ON(fs_access_mask < LANDLOCK_MASK_ACCESS_FS);
125}
126
127/**
128 * insert_rule - Create and insert a rule in a ruleset
129 *
130 * @ruleset: The ruleset to be updated.
131 * @object: The object to build the new rule with.  The underlying kernel
132 *          object must be held by the caller.
133 * @layers: One or multiple layers to be copied into the new rule.
134 * @num_layers: The number of @layers entries.
135 *
136 * When user space requests to add a new rule to a ruleset, @layers only
137 * contains one entry and this entry is not assigned to any level.  In this
138 * case, the new rule will extend @ruleset, similarly to a boolean OR between
139 * access rights.
140 *
141 * When merging a ruleset in a domain, or copying a domain, @layers will be
142 * added to @ruleset as new constraints, similarly to a boolean AND between
143 * access rights.
144 */
145static int insert_rule(struct landlock_ruleset *const ruleset,
146		       struct landlock_object *const object,
147		       const struct landlock_layer (*const layers)[],
148		       size_t num_layers)
149{
150	struct rb_node **walker_node;
151	struct rb_node *parent_node = NULL;
152	struct landlock_rule *new_rule;
153
154	might_sleep();
155	lockdep_assert_held(&ruleset->lock);
156	if (WARN_ON_ONCE(!object || !layers))
157		return -ENOENT;
158	walker_node = &(ruleset->root.rb_node);
159	while (*walker_node) {
160		struct landlock_rule *const this =
161			rb_entry(*walker_node, struct landlock_rule, node);
162
163		if (this->object != object) {
164			parent_node = *walker_node;
165			if (this->object < object)
166				walker_node = &((*walker_node)->rb_right);
167			else
168				walker_node = &((*walker_node)->rb_left);
169			continue;
170		}
171
172		/* Only a single-level layer should match an existing rule. */
173		if (WARN_ON_ONCE(num_layers != 1))
174			return -EINVAL;
175
176		/* If there is a matching rule, updates it. */
177		if ((*layers)[0].level == 0) {
178			/*
179			 * Extends access rights when the request comes from
180			 * landlock_add_rule(2), i.e. @ruleset is not a domain.
181			 */
182			if (WARN_ON_ONCE(this->num_layers != 1))
183				return -EINVAL;
184			if (WARN_ON_ONCE(this->layers[0].level != 0))
185				return -EINVAL;
186			this->layers[0].access |= (*layers)[0].access;
187			return 0;
188		}
189
190		if (WARN_ON_ONCE(this->layers[0].level == 0))
191			return -EINVAL;
192
193		/*
194		 * Intersects access rights when it is a merge between a
195		 * ruleset and a domain.
196		 */
197		new_rule = create_rule(object, &this->layers, this->num_layers,
198				       &(*layers)[0]);
199		if (IS_ERR(new_rule))
200			return PTR_ERR(new_rule);
201		rb_replace_node(&this->node, &new_rule->node, &ruleset->root);
202		free_rule(this);
203		return 0;
204	}
205
206	/* There is no match for @object. */
207	build_check_ruleset();
208	if (ruleset->num_rules >= LANDLOCK_MAX_NUM_RULES)
209		return -E2BIG;
210	new_rule = create_rule(object, layers, num_layers, NULL);
211	if (IS_ERR(new_rule))
212		return PTR_ERR(new_rule);
213	rb_link_node(&new_rule->node, parent_node, walker_node);
214	rb_insert_color(&new_rule->node, &ruleset->root);
215	ruleset->num_rules++;
216	return 0;
217}
218
219static void build_check_layer(void)
220{
221	const struct landlock_layer layer = {
222		.level = ~0,
223		.access = ~0,
224	};
225
226	BUILD_BUG_ON(layer.level < LANDLOCK_MAX_NUM_LAYERS);
227	BUILD_BUG_ON(layer.access < LANDLOCK_MASK_ACCESS_FS);
228}
229
230/* @ruleset must be locked by the caller. */
231int landlock_insert_rule(struct landlock_ruleset *const ruleset,
232			 struct landlock_object *const object,
233			 const access_mask_t access)
234{
235	struct landlock_layer layers[] = { {
236		.access = access,
237		/* When @level is zero, insert_rule() extends @ruleset. */
238		.level = 0,
239	} };
240
241	build_check_layer();
242	return insert_rule(ruleset, object, &layers, ARRAY_SIZE(layers));
243}
244
245static inline void get_hierarchy(struct landlock_hierarchy *const hierarchy)
246{
247	if (hierarchy)
248		refcount_inc(&hierarchy->usage);
249}
250
251static void put_hierarchy(struct landlock_hierarchy *hierarchy)
252{
253	while (hierarchy && refcount_dec_and_test(&hierarchy->usage)) {
254		const struct landlock_hierarchy *const freeme = hierarchy;
255
256		hierarchy = hierarchy->parent;
257		kfree(freeme);
258	}
259}
260
261static int merge_ruleset(struct landlock_ruleset *const dst,
262			 struct landlock_ruleset *const src)
263{
264	struct landlock_rule *walker_rule, *next_rule;
265	int err = 0;
266
267	might_sleep();
268	/* Should already be checked by landlock_merge_ruleset() */
269	if (WARN_ON_ONCE(!src))
270		return 0;
271	/* Only merge into a domain. */
272	if (WARN_ON_ONCE(!dst || !dst->hierarchy))
273		return -EINVAL;
274
275	/* Locks @dst first because we are its only owner. */
276	mutex_lock(&dst->lock);
277	mutex_lock_nested(&src->lock, SINGLE_DEPTH_NESTING);
278
279	/* Stacks the new layer. */
280	if (WARN_ON_ONCE(src->num_layers != 1 || dst->num_layers < 1)) {
281		err = -EINVAL;
282		goto out_unlock;
283	}
284	dst->fs_access_masks[dst->num_layers - 1] = src->fs_access_masks[0];
285
286	/* Merges the @src tree. */
287	rbtree_postorder_for_each_entry_safe(walker_rule, next_rule, &src->root,
288					     node) {
289		struct landlock_layer layers[] = { {
290			.level = dst->num_layers,
291		} };
292
293		if (WARN_ON_ONCE(walker_rule->num_layers != 1)) {
294			err = -EINVAL;
295			goto out_unlock;
296		}
297		if (WARN_ON_ONCE(walker_rule->layers[0].level != 0)) {
298			err = -EINVAL;
299			goto out_unlock;
300		}
301		layers[0].access = walker_rule->layers[0].access;
302		err = insert_rule(dst, walker_rule->object, &layers,
303				  ARRAY_SIZE(layers));
304		if (err)
305			goto out_unlock;
306	}
307
308out_unlock:
309	mutex_unlock(&src->lock);
310	mutex_unlock(&dst->lock);
311	return err;
312}
313
314static int inherit_ruleset(struct landlock_ruleset *const parent,
315			   struct landlock_ruleset *const child)
316{
317	struct landlock_rule *walker_rule, *next_rule;
318	int err = 0;
319
320	might_sleep();
321	if (!parent)
322		return 0;
323
324	/* Locks @child first because we are its only owner. */
325	mutex_lock(&child->lock);
326	mutex_lock_nested(&parent->lock, SINGLE_DEPTH_NESTING);
327
328	/* Copies the @parent tree. */
329	rbtree_postorder_for_each_entry_safe(walker_rule, next_rule,
330					     &parent->root, node) {
331		err = insert_rule(child, walker_rule->object,
332				  &walker_rule->layers,
333				  walker_rule->num_layers);
334		if (err)
335			goto out_unlock;
336	}
337
338	if (WARN_ON_ONCE(child->num_layers <= parent->num_layers)) {
339		err = -EINVAL;
340		goto out_unlock;
341	}
342	/* Copies the parent layer stack and leaves a space for the new layer. */
343	memcpy(child->fs_access_masks, parent->fs_access_masks,
344	       flex_array_size(parent, fs_access_masks, parent->num_layers));
345
346	if (WARN_ON_ONCE(!parent->hierarchy)) {
347		err = -EINVAL;
348		goto out_unlock;
349	}
350	get_hierarchy(parent->hierarchy);
351	child->hierarchy->parent = parent->hierarchy;
352
353out_unlock:
354	mutex_unlock(&parent->lock);
355	mutex_unlock(&child->lock);
356	return err;
357}
358
359static void free_ruleset(struct landlock_ruleset *const ruleset)
360{
361	struct landlock_rule *freeme, *next;
362
363	might_sleep();
364	rbtree_postorder_for_each_entry_safe(freeme, next, &ruleset->root, node)
365		free_rule(freeme);
366	put_hierarchy(ruleset->hierarchy);
367	kfree(ruleset);
368}
369
370void landlock_put_ruleset(struct landlock_ruleset *const ruleset)
371{
372	might_sleep();
373	if (ruleset && refcount_dec_and_test(&ruleset->usage))
374		free_ruleset(ruleset);
375}
376
377static void free_ruleset_work(struct work_struct *const work)
378{
379	struct landlock_ruleset *ruleset;
380
381	ruleset = container_of(work, struct landlock_ruleset, work_free);
382	free_ruleset(ruleset);
383}
384
385void landlock_put_ruleset_deferred(struct landlock_ruleset *const ruleset)
386{
387	if (ruleset && refcount_dec_and_test(&ruleset->usage)) {
388		INIT_WORK(&ruleset->work_free, free_ruleset_work);
389		schedule_work(&ruleset->work_free);
390	}
391}
392
393/**
394 * landlock_merge_ruleset - Merge a ruleset with a domain
395 *
396 * @parent: Parent domain.
397 * @ruleset: New ruleset to be merged.
398 *
399 * Returns the intersection of @parent and @ruleset, or returns @parent if
400 * @ruleset is empty, or returns a duplicate of @ruleset if @parent is empty.
401 */
402struct landlock_ruleset *
403landlock_merge_ruleset(struct landlock_ruleset *const parent,
404		       struct landlock_ruleset *const ruleset)
405{
406	struct landlock_ruleset *new_dom;
407	u32 num_layers;
408	int err;
409
410	might_sleep();
411	if (WARN_ON_ONCE(!ruleset || parent == ruleset))
412		return ERR_PTR(-EINVAL);
413
414	if (parent) {
415		if (parent->num_layers >= LANDLOCK_MAX_NUM_LAYERS)
416			return ERR_PTR(-E2BIG);
417		num_layers = parent->num_layers + 1;
418	} else {
419		num_layers = 1;
420	}
421
422	/* Creates a new domain... */
423	new_dom = create_ruleset(num_layers);
424	if (IS_ERR(new_dom))
425		return new_dom;
426	new_dom->hierarchy =
427		kzalloc(sizeof(*new_dom->hierarchy), GFP_KERNEL_ACCOUNT);
428	if (!new_dom->hierarchy) {
429		err = -ENOMEM;
430		goto out_put_dom;
431	}
432	refcount_set(&new_dom->hierarchy->usage, 1);
433
434	/* ...as a child of @parent... */
435	err = inherit_ruleset(parent, new_dom);
436	if (err)
437		goto out_put_dom;
438
439	/* ...and including @ruleset. */
440	err = merge_ruleset(new_dom, ruleset);
441	if (err)
442		goto out_put_dom;
443
444	return new_dom;
445
446out_put_dom:
447	landlock_put_ruleset(new_dom);
448	return ERR_PTR(err);
449}
450
451/*
452 * The returned access has the same lifetime as @ruleset.
453 */
454const struct landlock_rule *
455landlock_find_rule(const struct landlock_ruleset *const ruleset,
456		   const struct landlock_object *const object)
457{
458	const struct rb_node *node;
459
460	if (!object)
461		return NULL;
462	node = ruleset->root.rb_node;
463	while (node) {
464		struct landlock_rule *this =
465			rb_entry(node, struct landlock_rule, node);
466
467		if (this->object == object)
468			return this;
469		if (this->object < object)
470			node = node->rb_right;
471		else
472			node = node->rb_left;
473	}
474	return NULL;
475}
476