Restore persistent system path composition

crates/lazaret-core/src/configuration/confined_io.rs

@@ -265,6 +265,7 @@ fn validate_owned_directory(descriptor: &OwnedFd, uid: u32) -> Result<(), Config
 pub(super) fn validate_persistent_destinations(
     destinations: &[String],
     protected: &BTreeSet<String>,
+    nested_transient_overrides: &BTreeSet<String>,
 ) -> Result<Vec<String>, ConfigurationError> {
     require_pairwise_non_ancestral(
         destinations.iter().map(String::as_str),
@@ -272,11 +273,32 @@ pub(super) fn validate_persistent_destinations(
     )?;
     for destination in destinations {
         validate_sandbox_path(destination)?;
-        require_clear_of_protected(destination, protected)?;
+        require_persistent_clear_of_protected(destination, protected, nested_transient_overrides)?;
     }
     Ok(destinations.to_vec())
 }
 
+fn require_persistent_clear_of_protected(
+    destination: &str,
+    protected: &BTreeSet<String>,
+    nested_transient_overrides: &BTreeSet<String>,
+) -> Result<(), ConfigurationError> {
+    let conflict = protected.iter().any(|protected| {
+        destination == protected
+            || sandbox_is_strict_descendant(destination, protected)
+            || (sandbox_is_strict_descendant(protected, destination)
+                && !nested_transient_overrides.contains(protected))
+    });
+    if conflict {
+        Err(ConfigurationError::new(
+            ConfigurationErrorKind::PathConflict,
+            "configured sandbox destination intersects a protected destination",
+        ))
+    } else {
+        Ok(())
+    }
+}
+
 pub(super) fn require_clear_of_protected(
     destination: &str,
     protected: &BTreeSet<String>,

crates/lazaret-core/src/configuration/loading.rs

@@ -150,6 +150,7 @@ pub fn load_trusted_configuration(
     let persistent_dirs = validate_persistent_destinations(
         &selected.persistent_dirs,
         request.sandbox_layout.protected_destinations(),
+        request.sandbox_layout.nested_transient_overrides(),
     )?;
     let (effective_allow_prefixes, effective_deny_prefixes) =
         resolve_network(&configuration, selected)?;