Merge pull request casper-network#5207 from mpapierski/update-cargo-casper-2

Fix segfault in cargo-casper

Author: mpapierski

Cargo.lock

@@ -1,41 +1,15 @@
-use core::slice;
-use std::{ffi::c_void, path::Path, ptr::NonNull};
+use std::{mem::MaybeUninit, path::Path};
 
 use libloading::{Library, Symbol};
 
 const COLLECT_SCHEMA_FUNC: &str = "__cargo_casper_collect_schema";
 
-type CollectSchema = unsafe extern "C" fn(
-    callback: unsafe extern "C" fn(*const u8, usize, *mut c_void),
-    ctx: *mut c_void,
-);
+type CollectSchema = unsafe extern "C" fn(size_ptr: *mut u64) -> *mut u8;
 
 pub(crate) struct Artifact {
     library: Library,
 }
 
-unsafe extern "C" fn collect_schema_cb<T: FnOnce(&[u8])>(
-    data_ptr: *const u8,
-    data_len: usize,
-    ctx: *mut c_void,
-) {
-    let ptr: *mut Option<T> = ctx as _;
-    let data = slice::from_raw_parts(data_ptr, data_len);
-    let ptr = (*ptr).take().unwrap();
-    ptr(data);
-}
-
-fn collect_schema_helper<T>(library: &Library, cb: T)
-where
-    T: for<'a> FnOnce(&'a [u8]),
-{
-    let collect_schema: Symbol<CollectSchema> =
-        unsafe { library.get(COLLECT_SCHEMA_FUNC.as_bytes()).unwrap() };
-
-    let ptr = NonNull::from(&Some(cb));
-    unsafe { collect_schema(collect_schema_cb::<T>, ptr.as_ptr() as *mut _) };
-}
-
 impl Artifact {
     pub(crate) fn from_path<P: AsRef<Path>>(
         artifact_path: P,
@@ -50,12 +24,17 @@ impl Artifact {
     /// This returns a [`serde_json::Value`] to skip validation of a `Schema` object structure which
     /// (in theory) can differ.
     pub(crate) fn collect_schema(&self) -> serde_json::Result<serde_json::Value> {
-        let mut value = None;
-
-        collect_schema_helper(&self.library, |data| {
-            value = Some(serde_json::from_slice(data));
-        });
-
-        value.expect("Callback called")
+        let collect_schema: Symbol<CollectSchema> =
+            unsafe { self.library.get(COLLECT_SCHEMA_FUNC.as_bytes()).unwrap() };
+
+        let json_bytes = {
+            let mut value = MaybeUninit::uninit();
+            let leaked_json_bytes = unsafe { collect_schema(value.as_mut_ptr()) };
+            let size = unsafe { value.assume_init() };
+            let length: usize = size.try_into().unwrap();
+            unsafe { Vec::from_raw_parts(leaked_json_bytes, length, length) }
+        };
+
+        serde_json::from_slice(&json_bytes)
     }
 }

cargo-casper/src/cli/build_schema/artifact.rs

@@ -1,4 +1,4 @@
-use std::ffi::c_void;
+use core::{mem, ptr::NonNull};
 
 use crate::{
     abi::{Declaration, Definitions},
@@ -43,11 +43,16 @@ pub static ABI_COLLECTORS: [fn(&mut crate::abi::Definitions)] = [..];
 #[linkme(crate = crate::linkme)]
 pub static MESSAGES: [Message] = [..];
 
+/// This function is called by the host to collect the schema from the contract.
+///
+/// This is considered internal implementation detail and should not be used directly.
+/// Primary user of this API is `cargo-casper` tool that will use it to extract scheama from the
+/// contract.
+///
+/// # Safety
+/// Pointer to json bytes passed to the callback is valid only within the scope of that function.
 #[export_name = "__cargo_casper_collect_schema"]
-pub extern "C" fn cargo_casper_collect_schema(
-    callback: extern "C" fn(*const u8, usize, *mut c_void),
-    ctx: *mut c_void,
-) {
+pub unsafe extern "C" fn cargo_casper_collect_schema(size_ptr: *mut u64) -> *mut u8 {
     // Collect definitions
     let definitions = {
         let mut definitions = Definitions::default();
@@ -95,6 +100,11 @@ pub extern "C" fn cargo_casper_collect_schema(
     };
 
     // Write the schema using the provided writer
-    let json_bytes = serde_json::to_vec(&schema).expect("Serialized schema");
-    callback(json_bytes.as_ptr(), json_bytes.len(), ctx);
+    let mut json_bytes = serde_json::to_vec(&schema).expect("Serialized schema");
+    NonNull::new(size_ptr)
+        .expect("expected non-null ptr")
+        .write(json_bytes.len().try_into().expect("usize to u64"));
+    let ptr = json_bytes.as_mut_ptr();
+    mem::forget(json_bytes);
+    ptr
 }