[PATCH v1 5/9] landlock: Add extra checks when inserting a rule

[Mickaël Salaün]

Make sure that there is always an (allocated) object in each used rules.
This could have prevented the bug fixed with a previous commit.

When the rules from a ruleset are merged in a domain with
landlock_enforce_ruleset_current(2), these new rules should be assigned
to the last layer.  However, when a rule is just extending a ruleset
with landlock_add_rule(2), the number of layers of this updated ruleset
should always be 0.  Checking such use of landlock_insert_rule() could
enable to detect bugs in future developments.

Replace the hardcoded 1 with SINGLE_DEPTH_NESTING.

Cc: James Morris <jmorris@xxxxxxxxx>
Cc: Jann Horn <jannh@xxxxxxxxxx>
Cc: Serge E. Hallyn <serge@xxxxxxxxxx>
Signed-off-by: Mickaël Salaün <mic@xxxxxxxxxxx>
---
 security/landlock/ruleset.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/security/landlock/ruleset.c b/security/landlock/ruleset.c
index 7654a66cea43..1fb85daeb750 100644
--- a/security/landlock/ruleset.c
+++ b/security/landlock/ruleset.c
@@ -102,6 +102,10 @@ int landlock_insert_rule(struct landlock_ruleset *const ruleset,
 
 	might_sleep();
 	lockdep_assert_held(&ruleset->lock);
+	if (WARN_ON_ONCE(!rule->object))
+		return -ENOENT;
+	if (!is_merge && WARN_ON_ONCE(ruleset->nb_layers != 0))
+		return -EINVAL;
 	walker_node = &(ruleset->root.rb_node);
 	while (*walker_node) {
 		struct landlock_rule *const this = rb_entry(*walker_node,
@@ -223,12 +227,7 @@ static struct landlock_ruleset *inherit_ruleset(
 		return new_ruleset;
 
 	mutex_lock(&new_ruleset->lock);
-	mutex_lock_nested(&parent->lock, 1);
-	new_ruleset->nb_layers = parent->nb_layers;
-	new_ruleset->fs_access_mask = parent->fs_access_mask;
-	WARN_ON_ONCE(!parent->hierarchy);
-	get_hierarchy(parent->hierarchy);
-	new_ruleset->hierarchy->parent = parent->hierarchy;
+	mutex_lock_nested(&parent->lock, SINGLE_DEPTH_NESTING);
 
 	/* Copies the @parent tree. */
 	rbtree_postorder_for_each_entry_safe(walker_rule, next_rule,
@@ -237,6 +236,12 @@ static struct landlock_ruleset *inherit_ruleset(
 		if (err)
 			goto out_unlock;
 	}
+	new_ruleset->nb_layers = parent->nb_layers;
+	new_ruleset->fs_access_mask = parent->fs_access_mask;
+	WARN_ON_ONCE(!parent->hierarchy);
+	get_hierarchy(parent->hierarchy);
+	new_ruleset->hierarchy->parent = parent->hierarchy;
+
 	mutex_unlock(&parent->lock);
 	mutex_unlock(&new_ruleset->lock);
 	return new_ruleset;
-- 
2.29.2