[RFC PATCH v4 05/15] landlock: unmask_layers() function refactoring

[Konstantin Meskhidze]

Unmask_layers() helper function moves 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 at huawei.com>
---

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

---
 security/landlock/fs.c      | 67 +++++++++----------------------------
 security/landlock/ruleset.c | 44 ++++++++++++++++++++++++
 security/landlock/ruleset.h |  5 +++
 3 files changed, 64 insertions(+), 52 deletions(-)

diff --git a/security/landlock/fs.c b/security/landlock/fs.c
index 1497948d754f..75ebdce5cd16 100644
--- a/security/landlock/fs.c
+++ b/security/landlock/fs.c
@@ -178,51 +178,6 @@ int landlock_append_fs_rule(struct landlock_ruleset *const ruleset,
 	return err;
 }

-/* Access-control management */
-
-static inline u64 unmask_layers(
-		const struct landlock_ruleset *const domain,
-		const struct path *const path, const u32 access_request,
-		u64 layer_mask)
-{
-	const struct landlock_rule *rule;
-	const struct inode *inode;
-	size_t i;
-
-	if (d_is_negative(path->dentry))
-		/* Ignore nonexistent leafs. */
-		return layer_mask;
-	inode = d_backing_inode(path->dentry);
-	rcu_read_lock();
-	rule = landlock_find_rule(domain,
-			(uintptr_t)rcu_dereference(landlock_inode(inode)->object),
-			LANDLOCK_RULE_PATH_BENEATH);
-	rcu_read_unlock();
-	if (!rule)
-		return layer_mask;
-
-	/*
-	 * An access is granted if, for each policy layer, at least one rule
-	 * encountered on the pathwalk grants the requested accesses,
-	 * regardless of their position in the layer stack.  We must then check
-	 * the remaining layers for each inode, from the first added layer to
-	 * the last one.
-	 */
-	for (i = 0; i < rule->num_layers; i++) {
-		const struct landlock_layer *const layer = &rule->layers[i];
-		const u64 layer_level = BIT_ULL(layer->level - 1);
-
-		/* Checks that the layer grants access to the full request. */
-		if ((layer->access & access_request) == access_request) {
-			layer_mask &= ~layer_level;
-
-			if (layer_mask == 0)
-				return layer_mask;
-		}
-	}
-	return layer_mask;
-}
-
 static int check_access_path(const struct landlock_ruleset *const domain,
 		const struct path *const path, u32 access_request)
 {
@@ -268,15 +223,23 @@ static int check_access_path(const struct landlock_ruleset *const domain,
 	 */
 	while (true) {
 		struct dentry *parent_dentry;
+		const struct inode *inode;
+		struct landlock_object *object_ptr;

-		layer_mask = unmask_layers(domain, &walker_path,
-				access_request, layer_mask);
-		if (layer_mask == 0) {
-			/* Stops when a rule from each layer grants access. */
-			allowed = true;
-			break;
+		/* Ignore nonexistent leafs. */
+		if (!d_is_negative(walker_path.dentry)) {
+
+			inode = d_backing_inode(walker_path.dentry);
+			object_ptr = landlock_inode(inode)->object;
+			layer_mask = landlock_unmask_layers(domain, object_ptr,
+							access_request, layer_mask,
+							LANDLOCK_RULE_PATH_BENEATH);
+			if (layer_mask == 0) {
+				/* Stops when a rule from each layer grants access. */
+				allowed = true;
+				break;
+			}
 		}
-
 jump_up:
 		if (walker_path.dentry == walker_path.mnt->mnt_root) {
 			if (follow_up(&walker_path)) {
diff --git a/security/landlock/ruleset.c b/security/landlock/ruleset.c
index f2baa1c96b16..7179b10f3538 100644
--- a/security/landlock/ruleset.c
+++ b/security/landlock/ruleset.c
@@ -582,3 +582,47 @@ const struct landlock_rule *landlock_find_rule(
 	}
 	return NULL;
 }
+
+/* Access-control management */
+u64 landlock_unmask_layers(const struct landlock_ruleset *const domain,
+			   const struct landlock_object *object_ptr,
+			   const u32 access_request, u64 layer_mask,
+			   const u16 rule_type)
+{
+	const struct landlock_rule *rule;
+	size_t i;
+
+	switch (rule_type) {
+	case LANDLOCK_RULE_PATH_BENEATH:
+		rcu_read_lock();
+		rule = landlock_find_rule(domain,
+			(uintptr_t)rcu_dereference(object_ptr),
+			LANDLOCK_RULE_PATH_BENEATH);
+		rcu_read_unlock();
+		break;
+	}
+
+	if (!rule)
+		return layer_mask;
+
+	/*
+	 * An access is granted if, for each policy layer, at least one rule
+	 * encountered on the pathwalk grants the requested accesses,
+	 * regardless of their position in the layer stack.  We must then check
+	 * the remaining layers for each inode, from the first added layer to
+	 * the last one.
+	 */
+	for (i = 0; i < rule->num_layers; i++) {
+		const struct landlock_layer *const layer = &rule->layers[i];
+		const u64 layer_level = BIT_ULL(layer->level - 1);
+
+		/* Checks that the layer grants access to the full request. */
+		if ((layer->access & access_request) == access_request) {
+			layer_mask &= ~layer_level;
+
+			if (layer_mask == 0)
+				return layer_mask;
+		}
+	}
+	return layer_mask;
+}
diff --git a/security/landlock/ruleset.h b/security/landlock/ruleset.h
index 088b8d95f653..0a7d4b1f51fd 100644
--- a/security/landlock/ruleset.h
+++ b/security/landlock/ruleset.h
@@ -183,4 +183,9 @@ void landlock_set_fs_access_mask(struct landlock_ruleset *ruleset,

 u32 landlock_get_fs_access_mask(const struct landlock_ruleset *ruleset, u16 mask_level);

+u64 landlock_unmask_layers(const struct landlock_ruleset *const domain,
+			   const struct landlock_object *object_ptr,
+			   const u32 access_request, u64 layer_mask,
+			   const u16 rule_type);
+
 #endif /* _SECURITY_LANDLOCK_RULESET_H */
--
2.25.1