Use after free in Neon external buffersGHSA-8mj7-wxmc-f424

Neon provides functionality for creating JavaScript ArrayBuffer (and the Buffer subtype) instances backed by bytes allocated outside of V8/Node. The JsArrayBuffer::external and JsBuffer::external did not require T: 'static prior to Neon 0.10.1. This allowed creating an externally backed buffer from types that may be freed while they are still referenced by a JavaScript ArrayBuffer.

The following example demonstrates use after free. It compiles on versions <0.10.1 and fails to compile afterward.

pub fn soundness_hole(mut cx: FunctionContext) -> JsResult<JsArrayBuffer> {
    let mut data = vec![0u8, 1, 2, 3];
    
    // Creating an external from `&mut [u8]` instead of `Vec<u8>` since there is a blanket impl
    // of `AsMut<T> for &mut T`
    let buf = JsArrayBuffer::external(&mut cx, data.as_mut_slice());

    // `buf` is still holding a reference to `data`!
    drop(data);

    Ok(buf)
}