Add auto-deref workaround for ZeroizeOnDrop (#700)

RustCrypto · Jan 6, 2022 · de5f676 · de5f676
1 parent 3d9cd39
commit de5f676
Show file tree

Hide file tree

Showing 2 changed files with 36 additions and 7 deletions.
diff --git a/zeroize/derive/src/lib.rs b/zeroize/derive/src/lib.rs
@@ -69,11 +69,13 @@ fn derive_zeroize(mut s: synstructure::Structure<'_>) -> TokenStream {
 
 /// Custom derive for `ZeroizeOnDrop`
 fn derive_zeroize_on_drop(mut s: synstructure::Structure<'_>) -> TokenStream {
-    let zeroizers = generate_fields(&mut s);
+    let zeroizers = generate_fields(&mut s, quote! { zeroize_or_on_drop });
 
     let drop_impl = s.gen_impl(quote! {
         gen impl Drop for @Self {
             fn drop(&mut self) {
+                use zeroize::__internal::AssertZeroize;
+                use zeroize::__internal::AssertZeroizeOnDrop;
                 match self {
                     #zeroizers
                 }
@@ -251,7 +253,7 @@ impl ZeroizeAttrs {
     }
 }
 
-fn generate_fields(s: &mut synstructure::Structure<'_>) -> TokenStream {
+fn generate_fields(s: &mut synstructure::Structure<'_>, method: TokenStream) -> TokenStream {
     s.bind_with(|_| BindStyle::RefMut);
 
     s.filter_variants(|vi| {
@@ -265,7 +267,7 @@ fn generate_fields(s: &mut synstructure::Structure<'_>) -> TokenStream {
         result
     })
     .filter(|bi| filter_skip(&bi.ast().attrs, true))
-    .each(|bi| quote! { #bi.zeroize(); })
+    .each(|bi| quote! { #bi.#method(); })
 }
 
 fn filter_skip(attrs: &[Attribute], start: bool) -> bool {
@@ -291,7 +293,7 @@ fn filter_skip(attrs: &[Attribute], start: bool) -> bool {
 
 /// Custom derive for `Zeroize` (without `Drop`)
 fn derive_zeroize_without_drop(mut s: synstructure::Structure<'_>) -> TokenStream {
-    let zeroizers = generate_fields(&mut s);
+    let zeroizers = generate_fields(&mut s, quote! { zeroize });
 
     s.bound_impl(
         quote!(zeroize::Zeroize),
@@ -507,15 +509,17 @@ mod tests {
                 const _DERIVE_Drop_FOR_Z: () = {
                     impl Drop for Z {
                         fn drop(&mut self) {
+                            use zeroize::__internal::AssertZeroize;
+                            use zeroize::__internal::AssertZeroizeOnDrop;
                             match self {
                                 Z {
                                     a: ref mut __binding_0,
                                     b: ref mut __binding_1,
                                     c: ref mut __binding_2,
                                 } => {
-                                    { __binding_0.zeroize(); }
-                                    { __binding_1.zeroize(); }
-                                    { __binding_2.zeroize(); }
+                                    { __binding_0.zeroize_or_on_drop(); }
+                                    { __binding_1.zeroize_or_on_drop(); }
+                                    { __binding_2.zeroize_or_on_drop(); }
                                 }
                             }
                         }

diff --git a/zeroize/src/lib.rs b/zeroize/src/lib.rs
@@ -262,6 +262,31 @@ pub trait Zeroize {
 /// Marker trait signifying that this type will [`zeroize`](Zeroize::zeroize) itself on [`Drop`].
 pub trait ZeroizeOnDrop {}
 
+#[doc(hidden)]
+pub mod __internal {
+    use super::*;
+
+    /// Auto-deref workaround for deriving `ZeroizeOnDrop`.
+    pub trait AssertZeroizeOnDrop {
+        fn zeroize_or_on_drop(&mut self);
+    }
+
+    impl<T: ZeroizeOnDrop> AssertZeroizeOnDrop for &mut T {
+        fn zeroize_or_on_drop(&mut self) {}
+    }
+
+    /// Auto-deref workaround for deriving `ZeroizeOnDrop`.
+    pub trait AssertZeroize {
+        fn zeroize_or_on_drop(&mut self);
+    }
+
+    impl<T: Zeroize> AssertZeroize for T {
+        fn zeroize_or_on_drop(&mut self) {
+            self.zeroize()
+        }
+    }
+}
+
 /// Marker trait for types whose `Default` is the desired zeroization result
 pub trait DefaultIsZeroes: Copy + Default + Sized {}