jsc: replace MarkedArrayBuffer::from_bytes with an owning constructor

src/jsc/array_buffer.rs

@@ -923,15 +923,13 @@
     }
 
     pub fn from_string(str: &[u8]) -> Result<MarkedArrayBuffer, bun_alloc::AllocError> {
-        // allocator.dupe(u8, str) → Box::<[u8]>::from(str), but we need a raw
-        // pointer because the buffer is later freed via the default allocator
-        // (`MarkedArrayBuffer_deallocator` → `default_alloc::free`).
-        let buf: Box<[u8]> = Box::from(str);
-        let len = buf.len();
-        let ptr = bun_core::heap::into_raw(buf).cast::<u8>();
-        // SAFETY: ptr/len from heap::alloc; backed by the global allocator.
-        let bytes = unsafe { bun_core::ffi::slice_mut(ptr, len) };
-        Ok(MarkedArrayBuffer::from_bytes(bytes, JSType::Uint8Array))
+        // allocator.dupe(u8, str) → Box::<[u8]>::from(str); the buffer is later
+        // freed via the default allocator (`MarkedArrayBuffer_deallocator` →
+        // `default_alloc::free`).
+        Ok(MarkedArrayBuffer::from_owned_bytes(
+            Box::from(str),
+            JSType::Uint8Array,
+        ))
     }
 
     pub fn from_js(global: &JSGlobalObject, value: JSValue) -> Option<MarkedArrayBuffer> {
@@ -952,9 +950,13 @@
         })
     }
 
-    pub fn from_bytes(bytes: &mut [u8], typed_array_type: JSType) -> MarkedArrayBuffer {
+    /// Take ownership of a default-allocator `Box<[u8]>` and wrap it as an
+    /// owning `MarkedArrayBuffer`. The buffer is freed exactly once: either by
+    /// [`MarkedArrayBuffer::destroy`] or by the deallocator installed when the
+    /// buffer is handed to JSC (`to_js` / `to_node_buffer`).
+    pub fn from_owned_bytes(bytes: Box<[u8]>, typed_array_type: JSType) -> MarkedArrayBuffer {
         MarkedArrayBuffer {
-            buffer: ArrayBuffer::from_bytes(bytes, typed_array_type),
+            buffer: ArrayBuffer::from_owned_bytes(bytes, typed_array_type),
             owns_buffer: true,
             pinned: false,
         }
@@ -977,13 +979,19 @@
     }
 
     /// Releases the owned byte buffer if this `MarkedArrayBuffer` was created with an
-    /// allocator (e.g. via `from_string`/`from_bytes`). Does not free the struct itself;
+    /// allocator (e.g. via `from_string`/`from_owned_bytes`). Does not free the struct itself;
     /// `MarkedArrayBuffer` is passed and stored by value, so callers own its storage.
     pub fn destroy(&mut self) {
         if self.owns_buffer {
             self.owns_buffer = false;
-            // SAFETY: buffer.ptr was allocated by the global allocator (heap::alloc / allocator.dupe).
-            unsafe { bun_alloc::default_alloc::free(self.buffer.ptr.cast()) };
+            // An empty `Box<[u8]>` has no backing allocation — `from_owned_bytes`
+            // stored its dangling pointer, so there is nothing to free (same
+            // reasoning as `JSValue::create_buffer_from_box`).
+            if self.buffer.byte_len != 0 {
+                // SAFETY: `owns_buffer` is only set by `from_owned_bytes`, which
+                // took the pointer from a non-empty default-allocator `Box<[u8]>`.
+                unsafe { bun_alloc::default_alloc::free(self.buffer.ptr.cast()) };
+            }
         }
     }
 

src/runtime/api/bun/Terminal.rs

@@ -1796,11 +1796,11 @@ impl Terminal {
             return true;
         }
         v.extend_from_slice(chunk);
-        // MarkedArrayBuffer::from_bytes takes a `&mut [u8]` it will own (freed
-        // via mimalloc on the C++ side) — leak the Box and hand over the slice.
-        let bytes: &'static mut [u8] = Box::leak(v.into_boxed_slice());
-        let data = MarkedArrayBuffer::from_bytes(bytes, jsc::JSType::Uint8Array)
-            .to_node_buffer(global_this);
+        // Ownership of the boxed slice transfers to JSC (freed via the
+        // deallocator installed by `to_node_buffer`).
+        let data =
+            MarkedArrayBuffer::from_owned_bytes(v.into_boxed_slice(), jsc::JSType::Uint8Array)
+                .to_node_buffer(global_this);
 
         global_this.bun_vm().event_loop_mut().run_callback(
             callback,

src/runtime/api/bun/subprocess/SubprocessPipeReader.rs

@@ -308,14 +308,14 @@ impl PipeReader {
         match &mut self.state {
             State::Done(bytes) => {
                 let bytes = core::mem::take(bytes);
-                // `state.done` is now empty via `take()`.
-                // `MarkedArrayBuffer::from_bytes` takes a borrowed `&mut [u8]`
-                // with `owns_buffer = true` (freed via mimalloc on the JS side); leak the
-                // boxed slice so JS becomes the owner — same pattern as
-                // `MarkedArrayBuffer::from_string`.
-                let slice: &'static mut [u8] = Box::leak(bytes.into_boxed_slice());
-                MarkedArrayBuffer::from_bytes(slice, jsc::JSType::Uint8Array)
-                    .to_node_buffer(global_this)
+                // `state.done` is now empty via `take()`. Ownership of the
+                // boxed slice transfers to JSC (freed via the deallocator
+                // installed by `to_node_buffer`).
+                MarkedArrayBuffer::from_owned_bytes(
+                    bytes.into_boxed_slice(),
+                    jsc::JSType::Uint8Array,
+                )
+                .to_node_buffer(global_this)
             }
             _ => JSValue::UNDEFINED,
         }

src/runtime/node/node_fs.rs

@@ -7069,16 +7069,10 @@ impl NodeFS {
                     if let Some(file) = unsafe { &mut *graph }.find(path.as_bytes()) {
                         let contents: &[u8] = file.contents.as_bytes();
                         return if args.encoding == Encoding::Buffer {
-                            // PORTING.md §Forbidden bans `Vec::leak()`; round-trip through
-                            // `into_boxed_slice()` so the allocation layout JSC frees with
-                            // matches what we hand it (capacity == len).
-                            let raw =
-                                bun_core::heap::into_raw(contents.to_vec().into_boxed_slice());
-                            // SAFETY: ownership of the allocation is transferred to JSC; the
-                            // ArrayBuffer finalizer reconstructs the Box and frees it
-                            // (PORTING.md:348 — `heap::alloc`/`from_raw` across FFI).
-                            Ok(ret::ReadFileWithOptions::Buffer(Buffer::from_bytes(
-                                unsafe { &mut *raw },
+                            // Ownership of the boxed slice transfers to JSC; the
+                            // ArrayBuffer finalizer frees it.
+                            Ok(ret::ReadFileWithOptions::Buffer(Buffer::from_owned_bytes(
+                                contents.to_vec().into_boxed_slice(),
                                 bun_jsc::JSType::Uint8Array,
                             )))
                         } else if string_type == ReadFileStringType::Default {
@@ -7209,15 +7203,12 @@ impl NodeFS {
                             };
                         }
                     }
-                    let raw = bun_core::heap::into_raw(
+                    // Ownership of the boxed slice transfers to JSC; the
+                    // ArrayBuffer finalizer frees it.
+                    Ok(ret::ReadFileWithOptions::Buffer(Buffer::from_owned_bytes(
                         temporary_read_buffer_before_stat_call
                             .to_vec()
                             .into_boxed_slice(),
-                    );
-                    // SAFETY: ownership transferred to JSC; freed via ArrayBuffer finalizer
-                    // (PORTING.md:348 — `heap::alloc`/`from_raw` across FFI).
-                    Ok(ret::ReadFileWithOptions::Buffer(Buffer::from_bytes(
-                        unsafe { &mut *raw },
                         bun_jsc::JSType::Uint8Array,
                     )))
                 }
@@ -7377,11 +7368,10 @@ impl NodeFS {
         match args.encoding {
             Encoding::Buffer => {
                 buf.truncate(final_len);
-                let raw = bun_core::heap::into_raw(buf.into_boxed_slice());
-                // SAFETY: ownership transferred to JSC; freed via ArrayBuffer finalizer
-                // (PORTING.md:348 — `heap::alloc`/`from_raw` across FFI).
-                Ok(ret::ReadFileWithOptions::Buffer(Buffer::from_bytes(
-                    unsafe { &mut *raw },
+                // Ownership of the boxed slice transfers to JSC; the
+                // ArrayBuffer finalizer frees it.
+                Ok(ret::ReadFileWithOptions::Buffer(Buffer::from_owned_bytes(
+                    buf.into_boxed_slice(),
                     bun_jsc::JSType::Uint8Array,
                 )))
             }

src/runtime/shell/subproc.rs

@@ -2305,12 +2305,9 @@ impl PipeReader {
     pub fn to_buffer(&mut self, global_this: &JSGlobalObject) -> JSValue {
         match &mut self.state {
             PipeReaderState::Done(bytes) => {
-                // `MarkedArrayBuffer::from_bytes` adopts the allocation (freed
-                // by the JSC ArrayBuffer destructor). `heap::release` names that
-                // FFI hand-off — it is `Box::leak` under the hood; the JSC
-                // ArrayBuffer destructor is the reclaim, not this scope.
-                let slice: &'static mut [u8] = bun_core::heap::release(core::mem::take(bytes));
-                MarkedArrayBuffer::from_bytes(slice, jsc::JSType::Uint8Array)
+                // Ownership of the boxed slice transfers to JSC (freed via the
+                // deallocator installed by `to_node_buffer`).
+                MarkedArrayBuffer::from_owned_bytes(core::mem::take(bytes), jsc::JSType::Uint8Array)
                     .to_node_buffer(global_this)
             }
             _ => JSValue::UNDEFINED,

test/regression/marked-array-buffer-ownership-soundness-fixture/.gitignore

@@ -0,0 +1 @@
+/target