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 
create_ruleset(const u32 num_layers)27 static 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 
48 struct landlock_ruleset *
landlock_create_ruleset(const access_mask_t fs_access_mask)49 landlock_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 
build_check_rule(void)62 static 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 
71 static struct landlock_rule *
create_rule(struct landlock_object * const object,const struct landlock_layer (* const layers)[],const u32 num_layers,const struct landlock_layer * const new_layer)72 create_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 
free_rule(struct landlock_rule * const rule)105 static 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 
build_check_ruleset(void)114 static 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  */
insert_rule(struct landlock_ruleset * const ruleset,struct landlock_object * const object,const struct landlock_layer (* const layers)[],size_t num_layers)145 static 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 
build_check_layer(void)219 static 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. */
landlock_insert_rule(struct landlock_ruleset * const ruleset,struct landlock_object * const object,const access_mask_t access)231 int 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 
get_hierarchy(struct landlock_hierarchy * const hierarchy)245 static inline void get_hierarchy(struct landlock_hierarchy *const hierarchy)
246 {
247 	if (hierarchy)
248 		refcount_inc(&hierarchy->usage);
249 }
250 
put_hierarchy(struct landlock_hierarchy * hierarchy)251 static 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 
merge_ruleset(struct landlock_ruleset * const dst,struct landlock_ruleset * const src)261 static 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 
308 out_unlock:
309 	mutex_unlock(&src->lock);
310 	mutex_unlock(&dst->lock);
311 	return err;
312 }
313 
inherit_ruleset(struct landlock_ruleset * const parent,struct landlock_ruleset * const child)314 static 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 
353 out_unlock:
354 	mutex_unlock(&parent->lock);
355 	mutex_unlock(&child->lock);
356 	return err;
357 }
358 
free_ruleset(struct landlock_ruleset * const ruleset)359 static 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 
landlock_put_ruleset(struct landlock_ruleset * const ruleset)370 void 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 
free_ruleset_work(struct work_struct * const work)377 static 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 
landlock_put_ruleset_deferred(struct landlock_ruleset * const ruleset)385 void 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  */
402 struct landlock_ruleset *
landlock_merge_ruleset(struct landlock_ruleset * const parent,struct landlock_ruleset * const ruleset)403 landlock_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 
446 out_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  */
454 const struct landlock_rule *
landlock_find_rule(const struct landlock_ruleset * const ruleset,const struct landlock_object * const object)455 landlock_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