]> git.bitcoin.ninja Git - ldk-c-bindings/commitdiff
Provide full (new) struct to trait clone functions
authorMatt Corallo <git@bluematt.me>
Sun, 18 Jul 2021 02:09:45 +0000 (02:09 +0000)
committerMatt Corallo <git@bluematt.me>
Wed, 28 Jul 2021 17:06:58 +0000 (17:06 +0000)
Previously, when we went to clone a trait-implementation struct,
we'd provide only the `this_arg` void pointer, requiring that the
`this_arg` pointer be cloned into a new object while all remaining
fields are copied over exactly.

This has a few important limitations:
 * When a struct is cloned, it is not possible to set a `free`
   function to free any new data placed in `this_arg` without it
   also being set on the original struct.
 * Supertrait fields cannot be updated in the subtrait clone
   method, including the `this_arg` and `free` methods.

The first limitation prevents us from setting `free` after a clone
when the original trait may or may not have had `free` set. For
example, if the original trait was created with a `Obj_as_Trait`
method, cloned copies would never be free'd.

The second limitation prevents us from keeping the super and
subtrait `this_arg` fields in sync, in addition to limitations
similar to the above.

This resulted in Java code double-free'ing the `this_arg` field in
`InMemorySigner` objects which were accessed as both `Sign` and
`BaseSign` traits.

c-bindings-gen/src/main.rs

index b08f2348002a1e9f1b9671d493b730756a210e48..4c14074143966fe89b0f54c6979c5889ca4e87dc 100644 (file)
@@ -237,7 +237,7 @@ fn writeln_trait<'a, 'b, W: std::io::Write>(w: &mut W, t: &'a syn::ItemTrait, ty
        writeln!(w, "\t/// An opaque pointer which is passed to your function implementations as an argument.").unwrap();
        writeln!(w, "\t/// This has no meaning in the LDK, and can be NULL or any other value.").unwrap();
        writeln!(w, "\tpub this_arg: *mut c_void,").unwrap();
-       let mut generated_fields = Vec::new(); // Every field's (name, is_clonable) except this_arg, used in Clone generation
+       let mut generated_fields = Vec::new(); // Every field's (name, Option<clone_fn>) except this_arg, used in Clone generation
        for item in t.items.iter() {
                match item {
                        &syn::TraitItem::Method(ref m) => {
@@ -271,14 +271,14 @@ fn writeln_trait<'a, 'b, W: std::io::Write>(w: &mut W, t: &'a syn::ItemTrait, ty
                                                // happen) as well as provide an Option<>al function pointer which is
                                                // called when the trait method is called which allows updating on the fly.
                                                write!(w, "\tpub {}: ", m.sig.ident).unwrap();
-                                               generated_fields.push((format!("{}", m.sig.ident), true));
+                                               generated_fields.push((format!("{}", m.sig.ident), None));
                                                types.write_c_type(w, &*r.elem, Some(&meth_gen_types), false);
                                                writeln!(w, ",").unwrap();
                                                writeln!(w, "\t/// Fill in the {} field as a reference to it will be given to Rust after this returns", m.sig.ident).unwrap();
                                                writeln!(w, "\t/// Note that this takes a pointer to this object, not the this_ptr like other methods do").unwrap();
                                                writeln!(w, "\t/// This function pointer may be NULL if {} is filled in when this object is created and never needs updating.", m.sig.ident).unwrap();
                                                writeln!(w, "\tpub set_{}: Option<extern \"C\" fn(&{})>,", m.sig.ident, trait_name).unwrap();
-                                               generated_fields.push((format!("set_{}", m.sig.ident), true));
+                                               generated_fields.push((format!("set_{}", m.sig.ident), None));
                                                // Note that cbindgen will now generate
                                                // typedef struct Thing {..., set_thing: (const struct Thing*), ...} Thing;
                                                // which does not compile since Thing is not defined before it is used.
@@ -291,7 +291,7 @@ fn writeln_trait<'a, 'b, W: std::io::Write>(w: &mut W, t: &'a syn::ItemTrait, ty
                                }
 
                                write!(w, "\tpub {}: extern \"C\" fn (", m.sig.ident).unwrap();
-                               generated_fields.push((format!("{}", m.sig.ident), true));
+                               generated_fields.push((format!("{}", m.sig.ident), None));
                                write_method_params(w, &m.sig, "c_void", types, Some(&meth_gen_types), true, false);
                                writeln!(w, ",").unwrap();
                        },
@@ -300,29 +300,24 @@ fn writeln_trait<'a, 'b, W: std::io::Write>(w: &mut W, t: &'a syn::ItemTrait, ty
                }
        }
        // Add functions which may be required for supertrait implementations.
-       let mut requires_clone = false;
-       walk_supertraits!(t, Some(&types), (
-               ("Clone", _) => requires_clone = true,
-               (_, _) => {}
-       ) );
        walk_supertraits!(t, Some(&types), (
                ("Clone", _) => {
-                       writeln!(w, "\t/// Creates a copy of the object pointed to by this_arg, for a copy of this {}.", trait_name).unwrap();
-                       writeln!(w, "\t/// Note that the ultimate copy of the {} will have all function pointers the same as the original.", trait_name).unwrap();
-                       writeln!(w, "\t/// May be NULL if no action needs to be taken, the this_arg pointer will be copied into the new {}.", trait_name).unwrap();
-                       writeln!(w, "\tpub clone: Option<extern \"C\" fn (this_arg: *const c_void) -> *mut c_void>,").unwrap();
-                       generated_fields.push(("clone".to_owned(), true));
+                       writeln!(w, "\t/// Called, if set, after this {} has been cloned into a duplicate object.", trait_name).unwrap();
+                       writeln!(w, "\t/// The new {} is provided, and should be mutated as needed to perform a", trait_name).unwrap();
+                       writeln!(w, "\t/// deep copy of the object pointed to by this_arg or avoid any double-freeing.").unwrap();
+                       writeln!(w, "\tpub cloned: Option<extern \"C\" fn (new_{}: &mut {})>,", trait_name, trait_name).unwrap();
+                       generated_fields.push(("cloned".to_owned(), None));
                },
                ("std::cmp::Eq", _)|("core::cmp::Eq", _) => {
                        writeln!(w, "\t/// Checks if two objects are equal given this object's this_arg pointer and another object.").unwrap();
                        writeln!(w, "\tpub eq: extern \"C\" fn (this_arg: *const c_void, other_arg: &{}) -> bool,", trait_name).unwrap();
-                       generated_fields.push(("eq".to_owned(), true));
+                       generated_fields.push(("eq".to_owned(), None));
                },
                ("std::hash::Hash", _)|("core::hash::Hash", _) => {
                        writeln!(w, "\t/// Calculate a succinct non-cryptographic hash for an object given its this_arg pointer.").unwrap();
                        writeln!(w, "\t/// This is used, for example, for inclusion of this object in a hash map.").unwrap();
                        writeln!(w, "\tpub hash: extern \"C\" fn (this_arg: *const c_void) -> u64,").unwrap();
-                       generated_fields.push(("hash".to_owned(), true));
+                       generated_fields.push(("hash".to_owned(), None));
                },
                ("Send", _) => {}, ("Sync", _) => {},
                (s, i) => {
@@ -330,25 +325,22 @@ fn writeln_trait<'a, 'b, W: std::io::Write>(w: &mut W, t: &'a syn::ItemTrait, ty
                                let (docs, name, ret) = convert_trait_impl_field(s);
                                writeln!(w, "\t/// {}", docs).unwrap();
                                writeln!(w, "\tpub {}: extern \"C\" fn (this_arg: *const c_void) -> {},", name, ret).unwrap();
-                               (name, true) // Assume clonable
+                               (name, None) // Assume clonable
                        } else {
                                // For in-crate supertraits, just store a C-mapped copy of the supertrait as a member.
                                writeln!(w, "\t/// Implementation of {} for this object.", i).unwrap();
-                               writeln!(w, "\tpub {}: crate::{},", i, s).unwrap();
                                let is_clonable = types.is_clonable(s);
-                               if !is_clonable && requires_clone {
-                                       writeln!(w, "\t/// Creates a copy of the {}, for a copy of this {}.", i, trait_name).unwrap();
-                                       writeln!(w, "\t/// Because {} doesn't natively support copying itself, you have to provide a full copy implementation here.", i).unwrap();
-                                       writeln!(w, "\tpub {}_clone: extern \"C\" fn (orig_{}: &{}) -> {},", i, i, i, i).unwrap();
-                               }
-                               (format!("{}", i), is_clonable)
+                               writeln!(w, "\tpub {}: crate::{},", i, s).unwrap();
+                               (format!("{}", i), if !is_clonable {
+                                       Some(format!("crate::{}_clone_fields", s))
+                               } else { None })
                        });
                }
        ) );
        writeln!(w, "\t/// Frees any resources associated with this object given its this_arg pointer.").unwrap();
        writeln!(w, "\t/// Does not need to free the outer struct containing function pointers and may be NULL is no resources need to be freed.").unwrap();
        writeln!(w, "\tpub free: Option<extern \"C\" fn(this_arg: *mut c_void)>,").unwrap();
-       generated_fields.push(("free".to_owned(), true));
+       generated_fields.push(("free".to_owned(), None));
        writeln!(w, "}}").unwrap();
 
        macro_rules! impl_trait_for_c {
@@ -453,6 +445,20 @@ fn writeln_trait<'a, 'b, W: std::io::Write>(w: &mut W, t: &'a syn::ItemTrait, ty
        writeln!(w, "unsafe impl Send for {} {{}}", trait_name).unwrap();
        writeln!(w, "unsafe impl Sync for {} {{}}", trait_name).unwrap();
 
+       writeln!(w, "#[no_mangle]").unwrap();
+       writeln!(w, "pub(crate) extern \"C\" fn {}_clone_fields(orig: &{}) -> {} {{", trait_name, trait_name, trait_name).unwrap();
+       writeln!(w, "\t{} {{", trait_name).unwrap();
+       writeln!(w, "\t\tthis_arg: orig.this_arg,").unwrap();
+       for (field, clone_fn) in generated_fields.iter() {
+               if let Some(f) = clone_fn {
+                       // If the field isn't clonable, blindly assume its a trait and hope for the best.
+                       writeln!(w, "\t\t{}: {}(&orig.{}),", field, f, field).unwrap();
+               } else {
+                       writeln!(w, "\t\t{}: Clone::clone(&orig.{}),", field, field).unwrap();
+               }
+       }
+       writeln!(w, "\t}}\n}}").unwrap();
+
        // Implement supertraits for the C-mapped struct.
        walk_supertraits!(t, Some(&types), (
                ("std::cmp::Eq", _)|("core::cmp::Eq", _) => {
@@ -469,17 +475,9 @@ fn writeln_trait<'a, 'b, W: std::io::Write>(w: &mut W, t: &'a syn::ItemTrait, ty
                        writeln!(w, "#[no_mangle]").unwrap();
                        writeln!(w, "/// Creates a copy of a {}", trait_name).unwrap();
                        writeln!(w, "pub extern \"C\" fn {}_clone(orig: &{}) -> {} {{", trait_name, trait_name, trait_name).unwrap();
-                       writeln!(w, "\t{} {{", trait_name).unwrap();
-                       writeln!(w, "\t\tthis_arg: if let Some(f) = orig.clone {{ (f)(orig.this_arg) }} else {{ orig.this_arg }},").unwrap();
-                       for (field, clonable) in generated_fields.iter() {
-                               if *clonable {
-                                       writeln!(w, "\t\t{}: Clone::clone(&orig.{}),", field, field).unwrap();
-                               } else {
-                                       writeln!(w, "\t\t{}: (orig.{}_clone)(&orig.{}),", field, field, field).unwrap();
-                                       writeln!(w, "\t\t{}_clone: orig.{}_clone,", field, field).unwrap();
-                               }
-                       }
-                       writeln!(w, "\t}}\n}}").unwrap();
+                       writeln!(w, "\tlet mut res = {}_clone_fields(orig);", trait_name).unwrap();
+                       writeln!(w, "\tif let Some(f) = orig.cloned {{ (f)(&mut res) }};").unwrap();
+                       writeln!(w, "\tres\n}}").unwrap();
                        writeln!(w, "impl Clone for {} {{", trait_name).unwrap();
                        writeln!(w, "\tfn clone(&self) -> Self {{").unwrap();
                        writeln!(w, "\t\t{}_clone(self)", trait_name).unwrap();
@@ -805,13 +803,10 @@ fn writeln_impl<W: std::io::Write>(w: &mut W, i: &syn::ItemImpl, types: &mut Typ
                                                        }
                                                }
                                                let mut requires_clone = false;
-                                               walk_supertraits!(trait_obj, Some(&types), (
-                                                       ("Clone", _) => requires_clone = true,
-                                                       (_, _) => {}
-                                               ) );
                                                walk_supertraits!(trait_obj, Some(&types), (
                                                        ("Clone", _) => {
-                                                               writeln!(w, "\t\tclone: Some({}_clone_void),", ident).unwrap();
+                                                               requires_clone = true;
+                                                               writeln!(w, "\t\tcloned: Some({}_{}_cloned),", trait_obj.ident, ident).unwrap();
                                                        },
                                                        ("Sync", _) => {}, ("Send", _) => {},
                                                        ("std::marker::Sync", _) => {}, ("std::marker::Send", _) => {},
@@ -829,9 +824,6 @@ fn writeln_impl<W: std::io::Write>(w: &mut W, i: &syn::ItemImpl, types: &mut Typ
                                                                                }
                                                                        }
                                                                        write!(w, "\t\t}},\n").unwrap();
-                                                                       if !types.is_clonable(s) && requires_clone {
-                                                                               writeln!(w, "\t\t{}_clone: {}_{}_clone,", t, ident, t).unwrap();
-                                                                       }
                                                                } else {
                                                                        write_trait_impl_field_assign(w, s, ident);
                                                                }
@@ -916,27 +908,21 @@ fn writeln_impl<W: std::io::Write>(w: &mut W, i: &syn::ItemImpl, types: &mut Typ
                                                                _ => unimplemented!(),
                                                        }
                                                }
-                                               walk_supertraits!(trait_obj, Some(&types), (
-                                                       (s, t) => {
-                                                               if let Some(supertrait_obj) = types.crate_types.traits.get(s) {
-                                                                       if !types.is_clonable(s) && requires_clone {
-                                                                               writeln!(w, "extern \"C\" fn {}_{}_clone(orig: &crate::{}) -> crate::{} {{", ident, t, s, s).unwrap();
-                                                                               writeln!(w, "\tcrate::{} {{", s).unwrap();
-                                                                               writeln!(w, "\t\tthis_arg: orig.this_arg,").unwrap();
-                                                                               writeln!(w, "\t\tfree: None,").unwrap();
-                                                                               for item in supertrait_obj.items.iter() {
-                                                                                       match item {
-                                                                                               syn::TraitItem::Method(m) => {
-                                                                                                       write_meth!(m, supertrait_obj, "");
-                                                                                               },
-                                                                                               _ => {},
-                                                                                       }
-                                                                               }
-                                                                               write!(w, "\t}}\n}}\n").unwrap();
+                                               if requires_clone {
+                                                       writeln!(w, "extern \"C\" fn {}_{}_cloned(new_obj: &mut crate::{}) {{", trait_obj.ident, ident, full_trait_path).unwrap();
+                                                       writeln!(w, "\tnew_obj.this_arg = {}_clone_void(new_obj.this_arg);", ident).unwrap();
+                                                       writeln!(w, "\tnew_obj.free = Some({}_free_void);", ident).unwrap();
+                                                       walk_supertraits!(trait_obj, Some(&types), (
+                                                               (s, t) => {
+                                                                       if types.crate_types.traits.get(s).is_some() {
+                                                                               assert!(!types.is_clonable(s)); // We don't currently support cloning with a clonable supertrait
+                                                                               writeln!(w, "\tnew_obj.{}.this_arg = new_obj.this_arg;", t).unwrap();
+                                                                               writeln!(w, "\tnew_obj.{}.free = None;", t).unwrap();
                                                                        }
                                                                }
-                                                       }
-                                               ) );
+                                                       ) );
+                                                       writeln!(w, "}}").unwrap();
+                                               }
                                                write!(w, "\n").unwrap();
                                        } else if path_matches_nongeneric(&trait_path.1, &["From"]) {
                                        } else if path_matches_nongeneric(&trait_path.1, &["Default"]) {