Date:   Mon, 16 May 2022 23:20:27 +0800
From:   Konstantin Meskhidze <konstantin.meskhidze@...wei.com>
To:     <mic@...ikod.net>
CC:     <willemdebruijn.kernel@...il.com>,
        <linux-security-module@...r.kernel.org>, <netdev@...r.kernel.org>,
        <netfilter-devel@...r.kernel.org>, <yusongping@...wei.com>,
        <anton.sirazetdinov@...wei.com>
Subject: [PATCH v5 04/15] landlock: helper functions refactoring

Unmask_layers(), init_layer_masks() and
get_handled_accesses() helper functions move to
ruleset.c and rule_type argument is added.
This modification supports implementing new rule
types into next landlock versions.

Signed-off-by: Konstantin Meskhidze <konstantin.meskhidze@...wei.com>
---

Changes since v3:
* Splits commit.
* Refactoring landlock_unmask_layers functions.

Changes since v4:
* Refactoring init_layer_masks(), get_handled_accesses()
and unmask_layers() functions to support multiple rule types.
* Refactoring landlock_get_fs_access_mask() function with
LANDLOCK_MASK_ACCESS_FS mask.

---
 security/landlock/fs.c      | 158 ++++++++----------------------------
 security/landlock/ruleset.c | 152 +++++++++++++++++++++++++++++++---
 security/landlock/ruleset.h |  17 +++-
 3 files changed, 192 insertions(+), 135 deletions(-)

diff --git a/security/landlock/fs.c b/security/landlock/fs.c
index 5de24d4dd74c..3506e182b23e 100644
--- a/security/landlock/fs.c
+++ b/security/landlock/fs.c
@@ -211,60 +211,6 @@ find_rule(const struct landlock_ruleset *const domain,
 	return rule;
 }

-/*
- * @layer_masks is read and may be updated according to the access request and
- * the matching rule.
- *
- * Returns true if the request is allowed (i.e. relevant layer masks for the
- * request are empty).
- */
-static inline bool
-unmask_layers(const struct landlock_rule *const rule,
-	      const access_mask_t access_request,
-	      layer_mask_t (*const layer_masks)[LANDLOCK_NUM_ACCESS_FS])
-{
-	size_t layer_level;
-
-	if (!access_request || !layer_masks)
-		return true;
-	if (!rule)
-		return false;
-
-	/*
-	 * An access is granted if, for each policy layer, at least one rule
-	 * encountered on the pathwalk grants the requested access,
-	 * regardless of its position in the layer stack.  We must then check
-	 * the remaining layers for each inode, from the first added layer to
-	 * the last one.  When there is multiple requested accesses, for each
-	 * policy layer, the full set of requested accesses may not be granted
-	 * by only one rule, but by the union (binary OR) of multiple rules.
-	 * E.g. /a/b <execute> + /a <read> => /a/b <execute + read>
-	 */
-	for (layer_level = 0; layer_level < rule->num_layers; layer_level++) {
-		const struct landlock_layer *const layer =
-			&rule->layers[layer_level];
-		const layer_mask_t layer_bit = BIT_ULL(layer->level - 1);
-		const unsigned long access_req = access_request;
-		unsigned long access_bit;
-		bool is_empty;
-
-		/*
-		 * Records in @layer_masks which layer grants access to each
-		 * requested access.
-		 */
-		is_empty = true;
-		for_each_set_bit(access_bit, &access_req,
-				 ARRAY_SIZE(*layer_masks)) {
-			if (layer->access & BIT_ULL(access_bit))
-				(*layer_masks)[access_bit] &= ~layer_bit;
-			is_empty = is_empty && !(*layer_masks)[access_bit];
-		}
-		if (is_empty)
-			return true;
-	}
-	return false;
-}
-
 /*
  * Allows access to pseudo filesystems that will never be mountable (e.g.
  * sockfs, pipefs), but can still be reachable through
@@ -277,59 +223,6 @@ static inline bool is_nouser_or_private(const struct dentry *dentry)
 		unlikely(IS_PRIVATE(d_backing_inode(dentry))));
 }

-static inline access_mask_t
-get_handled_accesses(const struct landlock_ruleset *const domain)
-{
-	access_mask_t access_dom = 0;
-	unsigned long access_bit;
-
-	for (access_bit = 0; access_bit < LANDLOCK_NUM_ACCESS_FS;
-	     access_bit++) {
-		size_t layer_level;
-
-		for (layer_level = 0; layer_level < domain->num_layers;
-				layer_level++) {
-			if (landlock_get_fs_access_mask(domain, layer_level) &
-					BIT_ULL(access_bit)) {
-				access_dom |= BIT_ULL(access_bit);
-				break;
-			}
-		}
-	}
-	return access_dom;
-}
-
-static inline access_mask_t
-init_layer_masks(const struct landlock_ruleset *const domain,
-		 const access_mask_t access_request,
-		 layer_mask_t (*const layer_masks)[LANDLOCK_NUM_ACCESS_FS])
-{
-	access_mask_t handled_accesses = 0;
-	size_t layer_level;
-
-	memset(layer_masks, 0, sizeof(*layer_masks));
-	/* An empty access request can happen because of O_WRONLY | O_RDWR. */
-	if (!access_request)
-		return 0;
-
-	/* Saves all handled accesses per layer. */
-	for (layer_level = 0; layer_level < domain->num_layers; layer_level++) {
-		const unsigned long access_req = access_request;
-		unsigned long access_bit;
-
-		for_each_set_bit(access_bit, &access_req,
-				ARRAY_SIZE(*layer_masks)) {
-			if (landlock_get_fs_access_mask(domain, layer_level) &
-					BIT_ULL(access_bit)) {
-				(*layer_masks)[access_bit] |=
-					BIT_ULL(layer_level);
-				handled_accesses |= BIT_ULL(access_bit);
-			}
-		}
-	}
-	return handled_accesses;
-}
-
 /*
  * Check that a destination file hierarchy has more restrictions than a source
  * file hierarchy.  This is only used for link and rename actions.
@@ -506,7 +399,8 @@ static int check_access_path_dual(
 		 * a superset of the meaningful requested accesses).
 		 */
 		access_masked_parent1 = access_masked_parent2 =
-			get_handled_accesses(domain);
+			get_handled_accesses(domain, LANDLOCK_RULE_PATH_BENEATH,
+					     LANDLOCK_NUM_ACCESS_FS);
 		is_dom_check = true;
 	} else {
 		if (WARN_ON_ONCE(dentry_child1 || dentry_child2))
@@ -519,17 +413,25 @@ static int check_access_path_dual(

 	if (unlikely(dentry_child1)) {
 		unmask_layers(find_rule(domain, dentry_child1),
-			      init_layer_masks(domain, LANDLOCK_MASK_ACCESS_FS,
-					       &_layer_masks_child1),
-			      &_layer_masks_child1);
+				init_layer_masks(domain,
+					LANDLOCK_MASK_ACCESS_FS,
+					&_layer_masks_child1,
+					sizeof(_layer_masks_child1),
+					LANDLOCK_RULE_PATH_BENEATH),
+				&_layer_masks_child1,
+				ARRAY_SIZE(_layer_masks_child1));
 		layer_masks_child1 = &_layer_masks_child1;
 		child1_is_directory = d_is_dir(dentry_child1);
 	}
 	if (unlikely(dentry_child2)) {
 		unmask_layers(find_rule(domain, dentry_child2),
-			      init_layer_masks(domain, LANDLOCK_MASK_ACCESS_FS,
-					       &_layer_masks_child2),
-			      &_layer_masks_child2);
+				init_layer_masks(domain,
+					LANDLOCK_MASK_ACCESS_FS,
+					&_layer_masks_child2,
+					sizeof(_layer_masks_child2),
+					LANDLOCK_RULE_PATH_BENEATH),
+				&_layer_masks_child2,
+				ARRAY_SIZE(_layer_masks_child2));
 		layer_masks_child2 = &_layer_masks_child2;
 		child2_is_directory = d_is_dir(dentry_child2);
 	}
@@ -582,14 +484,15 @@ static int check_access_path_dual(

 		rule = find_rule(domain, walker_path.dentry);
 		allowed_parent1 = unmask_layers(rule, access_masked_parent1,
-						layer_masks_parent1);
+				layer_masks_parent1,
+				ARRAY_SIZE(*layer_masks_parent1));
 		allowed_parent2 = unmask_layers(rule, access_masked_parent2,
-						layer_masks_parent2);
+				layer_masks_parent2,
+				ARRAY_SIZE(*layer_masks_parent2));

 		/* Stops when a rule from each layer grants access. */
 		if (allowed_parent1 && allowed_parent2)
 			break;
-
 jump_up:
 		if (walker_path.dentry == walker_path.mnt->mnt_root) {
 			if (follow_up(&walker_path)) {
@@ -645,7 +548,9 @@ static inline int check_access_path(const struct landlock_ruleset *const domain,
 {
 	layer_mask_t layer_masks[LANDLOCK_NUM_ACCESS_FS] = {};

-	access_request = init_layer_masks(domain, access_request, &layer_masks);
+	access_request = init_layer_masks(domain, access_request,
+			&layer_masks, sizeof(layer_masks),
+			LANDLOCK_RULE_PATH_BENEATH);
 	return check_access_path_dual(domain, path, access_request,
 				      &layer_masks, NULL, 0, NULL, NULL);
 }
@@ -729,7 +634,8 @@ static bool collect_domain_accesses(
 		return true;

 	access_dom = init_layer_masks(domain, LANDLOCK_MASK_ACCESS_FS,
-				      layer_masks_dom);
+			layer_masks_dom, sizeof(*layer_masks_dom),
+			LANDLOCK_RULE_PATH_BENEATH);

 	dget(dir);
 	while (true) {
@@ -737,7 +643,8 @@ static bool collect_domain_accesses(

 		/* Gets all layers allowing all domain accesses. */
 		if (unmask_layers(find_rule(domain, dir), access_dom,
-				  layer_masks_dom)) {
+					layer_masks_dom,
+					ARRAY_SIZE(*layer_masks_dom))) {
 			/*
 			 * Stops when all handled accesses are allowed by at
 			 * least one rule in each layer.
@@ -851,9 +758,10 @@ static int current_check_refer_path(struct dentry *const old_dentry,
 		 * The LANDLOCK_ACCESS_FS_REFER access right is not required
 		 * for same-directory referer (i.e. no reparenting).
 		 */
-		access_request_parent1 = init_layer_masks(
-			dom, access_request_parent1 | access_request_parent2,
-			&layer_masks_parent1);
+		access_request_parent1 = init_layer_masks(dom,
+				access_request_parent1 | access_request_parent2,
+				&layer_masks_parent1, sizeof(layer_masks_parent1),
+				LANDLOCK_RULE_PATH_BENEATH);
 		return check_access_path_dual(dom, new_dir,
 					      access_request_parent1,
 					      &layer_masks_parent1, NULL, 0,
@@ -861,7 +769,9 @@ static int current_check_refer_path(struct dentry *const old_dentry,
 	}

 	/* Backward compatibility: no reparenting support. */
-	if (!(get_handled_accesses(dom) & LANDLOCK_ACCESS_FS_REFER))
+	if (!(get_handled_accesses(dom, LANDLOCK_RULE_PATH_BENEATH,
+				   LANDLOCK_NUM_ACCESS_FS) &
+						LANDLOCK_ACCESS_FS_REFER))
 		return -EXDEV;

 	access_request_parent1 |= LANDLOCK_ACCESS_FS_REFER;
diff --git a/security/landlock/ruleset.c b/security/landlock/ruleset.c
index 4b4c9953bb32..c4ed783d655b 100644
--- a/security/landlock/ruleset.c
+++ b/security/landlock/ruleset.c
@@ -233,7 +233,8 @@ static int insert_rule(struct landlock_ruleset *const ruleset,
 					       &(*layers)[0]);
 			if (IS_ERR(new_rule))
 				return PTR_ERR(new_rule);
-			rb_replace_node(&this->node, &new_rule->node, &ruleset->root_inode);
+			rb_replace_node(&this->node, &new_rule->node,
+					&ruleset->root_inode);
 			free_rule(this, rule_type);
 			break;
 		}
@@ -246,7 +247,8 @@ static int insert_rule(struct landlock_ruleset *const ruleset,
 		return -E2BIG;
 	switch (rule_type) {
 	case LANDLOCK_RULE_PATH_BENEATH:
-		new_rule = create_rule(object_ptr, 0, layers, num_layers, NULL);
+		new_rule = create_rule(object_ptr, 0, layers,
+				       num_layers, NULL);
 		if (IS_ERR(new_rule))
 			return PTR_ERR(new_rule);
 		rb_link_node(&new_rule->node, parent_node, walker_node);
@@ -281,8 +283,8 @@ int landlock_insert_rule(struct landlock_ruleset *const ruleset,
 	} };

 	build_check_layer();
-	return insert_rule(ruleset, object_ptr, object_data, rule_type, &layers,
-			   ARRAY_SIZE(layers));
+	return insert_rule(ruleset, object_ptr, object_data, rule_type,
+			   &layers, ARRAY_SIZE(layers));
 }

 static inline void get_hierarchy(struct landlock_hierarchy *const hierarchy)
@@ -335,8 +337,9 @@ static int tree_merge(struct landlock_ruleset *const src,

 		switch (rule_type) {
 		case LANDLOCK_RULE_PATH_BENEATH:
-			err = insert_rule(dst, walker_rule->object.ptr, 0, rule_type,
-					  &layers, ARRAY_SIZE(layers));
+			err = insert_rule(dst, walker_rule->object.ptr, 0,
+					  rule_type, &layers,
+					  ARRAY_SIZE(layers));
 			break;
 		}
 		if (err)
@@ -433,9 +436,13 @@ static int inherit_ruleset(struct landlock_ruleset *const parent,
 		err = -EINVAL;
 		goto out_unlock;
 	}
-	/* Copies the parent layer stack and leaves a space for the new layer. */
+	/*
+	 * Copies the parent layer stack and leaves a space
+	 * for the new layer.
+	 */
 	memcpy(child->access_masks, parent->access_masks,
-			flex_array_size(parent, access_masks, parent->num_layers));
+			flex_array_size(parent, access_masks,
+					parent->num_layers));

 	if (WARN_ON_ONCE(!parent->hierarchy)) {
 		err = -EINVAL;
@@ -455,8 +462,9 @@ static void free_ruleset(struct landlock_ruleset *const ruleset)
 	struct landlock_rule *freeme, *next;

 	might_sleep();
-	rbtree_postorder_for_each_entry_safe(freeme, next, &ruleset->root_inode,
-			node)
+	rbtree_postorder_for_each_entry_safe(freeme, next,
+					     &ruleset->root_inode,
+					     node)
 		free_rule(freeme, LANDLOCK_RULE_PATH_BENEATH);
 	put_hierarchy(ruleset->hierarchy);
 	kfree(ruleset);
@@ -577,3 +585,127 @@ const struct landlock_rule *landlock_find_rule(
 	}
 	return NULL;
 }
+
+access_mask_t get_handled_accesses(
+		const struct landlock_ruleset *const domain,
+		u16 rule_type, u16 num_access)
+{
+	access_mask_t access_dom = 0;
+	unsigned long access_bit;
+
+	switch (rule_type) {
+	case LANDLOCK_RULE_PATH_BENEATH:
+		for (access_bit = 0; access_bit < LANDLOCK_NUM_ACCESS_FS;
+			access_bit++) {
+			size_t layer_level;
+
+			for (layer_level = 0; layer_level < domain->num_layers;
+					layer_level++) {
+				if (landlock_get_fs_access_mask(domain,
+								layer_level) &
+						BIT_ULL(access_bit)) {
+					access_dom |= BIT_ULL(access_bit);
+					break;
+				}
+			}
+		}
+		break;
+	default:
+		break;
+	}
+	return access_dom;
+}
+
+/*
+ * @layer_masks is read and may be updated according to the access request and
+ * the matching rule.
+ *
+ * Returns true if the request is allowed (i.e. relevant layer masks for the
+ * request are empty).
+ */
+bool unmask_layers(const struct landlock_rule *const rule,
+		const access_mask_t access_request,
+		layer_mask_t (*const layer_masks)[], size_t masks_array_size)
+{
+	size_t layer_level;
+
+	if (!access_request || !layer_masks)
+		return true;
+	if (!rule)
+		return false;
+
+	/*
+	 * An access is granted if, for each policy layer, at least one rule
+	 * encountered on the pathwalk grants the requested access,
+	 * regardless of its position in the layer stack.  We must then check
+	 * the remaining layers for each inode, from the first added layer to
+	 * the last one.  When there is multiple requested accesses, for each
+	 * policy layer, the full set of requested accesses may not be granted
+	 * by only one rule, but by the union (binary OR) of multiple rules.
+	 * E.g. /a/b <execute> + /a <read> => /a/b <execute + read>
+	 */
+	for (layer_level = 0; layer_level < rule->num_layers; layer_level++) {
+		const struct landlock_layer *const layer =
+			&rule->layers[layer_level];
+		const layer_mask_t layer_bit = BIT_ULL(layer->level - 1);
+		const unsigned long access_req = access_request;
+		unsigned long access_bit;
+		bool is_empty;
+
+		/*
+		 * Records in @layer_masks which layer grants access to each
+		 * requested access.
+		 */
+		is_empty = true;
+		for_each_set_bit(access_bit, &access_req, masks_array_size) {
+			if (layer->access & BIT_ULL(access_bit))
+				(*layer_masks)[access_bit] &= ~layer_bit;
+			is_empty = is_empty && !(*layer_masks)[access_bit];
+		}
+		if (is_empty)
+			return true;
+	}
+	return false;
+}
+
+access_mask_t init_layer_masks(const struct landlock_ruleset *const domain,
+			       const access_mask_t access_request,
+			       layer_mask_t (*const layer_masks)[],
+			       size_t masks_size,
+			       u16 rule_type)
+{
+	access_mask_t handled_accesses = 0;
+	size_t layer_level;
+
+	memset(layer_masks, 0, masks_size);
+
+	/* An empty access request can happen because of O_WRONLY | O_RDWR. */
+	if (!access_request)
+		return 0;
+
+	/* Saves all handled accesses per layer. */
+	for (layer_level = 0; layer_level < domain->num_layers;
+			layer_level++) {
+		const unsigned long access_req = access_request;
+		unsigned long access_bit;
+
+		switch (rule_type) {
+		case LANDLOCK_RULE_PATH_BENEATH:
+			for_each_set_bit(access_bit, &access_req,
+					LANDLOCK_NUM_ACCESS_FS) {
+				if (landlock_get_fs_access_mask(domain,
+								layer_level) &
+						BIT_ULL(access_bit)) {
+					(*layer_masks)[access_bit] |=
+						BIT_ULL(layer_level);
+					handled_accesses |=
+							   BIT_ULL(access_bit);
+				}
+			}
+			break;
+		default:
+			return 0;
+		}
+	}
+	return handled_accesses;
+}
diff --git a/security/landlock/ruleset.h b/security/landlock/ruleset.h
index 3066e5d7180c..f3cd890d0348 100644
--- a/security/landlock/ruleset.h
+++ b/security/landlock/ruleset.h
@@ -195,7 +195,22 @@ static inline u32 landlock_get_fs_access_mask(
 					const struct landlock_ruleset *ruleset,
 					u16 mask_level)
 {
-	return ruleset->access_masks[mask_level];
+	return (ruleset->access_masks[mask_level] & LANDLOCK_MASK_ACCESS_FS);
 }

+access_mask_t get_handled_accesses(
+		const struct landlock_ruleset *const domain,
+		u16 rule_type, u16 num_access);
+
+bool unmask_layers(const struct landlock_rule *const rule,
+		   const access_mask_t access_request,
+		   layer_mask_t (*const layer_masks)[],
+		   size_t masks_array_size);
+
+access_mask_t init_layer_masks(const struct landlock_ruleset *const domain,
+			       const access_mask_t access_request,
+			       layer_mask_t (*const layer_masks)[],
+			       size_t masks_size,
+			       u16 rule_type);
+
 #endif /* _SECURITY_LANDLOCK_RULESET_H */
--
2.25.1

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