From: Matt Corallo <git@bluematt.me>
Date: Mon, 29 Nov 2021 01:28:30 +0000 (+0000)
Subject: Expose a method to unmangle pointers in test builds
X-Git-Tag: v0.0.103.1^2~3
X-Git-Url: http://git.bitcoin.ninja/index.cgi?p=ldk-c-bindings;a=commitdiff_plain;h=ce0ec2494f33662d8cfb14efc00cb49d22190e2c

Expose a method to unmangle pointers in test builds

This is used by Java bindings to compare all pointers against those
returned by its malloc wrap, possibly catching some simple
use-after-free or invalid pointer deref bugs.

It is exposed only when built as debug and defined in C headers
with `LDK_DEBUG_BUILD` defined.
---

diff --git a/lightning-c-bindings/cbindgen.toml b/lightning-c-bindings/cbindgen.toml
index ec6c74d..f49d50e 100644
--- a/lightning-c-bindings/cbindgen.toml
+++ b/lightning-c-bindings/cbindgen.toml
@@ -29,3 +29,6 @@ must_use = "MUST_USE_ENUM"
 
 [ptr]
 non_null_attribute = "NONNULL_PTR"
+
+[defines]
+"test_mod_pointers" = "LDK_DEBUG_BUILD"
diff --git a/lightning-c-bindings/src/c_types/mod.rs b/lightning-c-bindings/src/c_types/mod.rs
index 3d6f08a..98e964f 100644
--- a/lightning-c-bindings/src/c_types/mod.rs
+++ b/lightning-c-bindings/src/c_types/mod.rs
@@ -14,7 +14,7 @@ use bitcoin::secp256k1::recovery::RecoverableSignature as SecpRecoverableSignatu
 use bitcoin::bech32;
 
 use std::convert::TryInto; // Bindings need at least rustc 1.34
-
+use core::ffi::c_void;
 use std::io::{Cursor, Read}; // TODO: We should use core2 here when we support no_std
 
 #[repr(C)]
@@ -618,6 +618,18 @@ pub(crate) mod ObjOps {
 	}
 }
 
+#[cfg(test_mod_pointers)]
+#[no_mangle]
+/// This function exists for memory safety testing purposes. It should never be used in production
+/// code
+pub extern "C" fn __unmangle_inner_ptr(ptr: *const c_void) -> *const c_void {
+	if ptr as usize == 1 {
+		core::ptr::null()
+	} else {
+		unsafe { ptr.cast::<u8>().sub(4096).cast::<c_void>() }
+	}
+}
+
 pub(crate) struct SmartPtr<T> {
 	ptr: *mut T,
 }