Rust: Segfault because of self-referential structs

[TethysSvensson]

If you make a self-referential structs in flatbuffers, it still compiles, but outputs invalid code:

struct Foo {
  x: uint64;
  inner_foo: Foo;
}

table Root {
  foo: Foo;
}

mod foo_generated;
use foo_generated::*;

fn main() {
    let mut builder = flatbuffers::FlatBufferBuilder::new();
    let mut foo = Foo::default();
    foo.set_x(17);
    let root = Root::create(&mut builder, &RootArgs { foo: Some(&foo) });
    builder.finish(root, None);
    let data = builder.finished_data();

    // For fun, let's use the stack to decode
    let mut stack_buf = [0; 64];
    stack_buf[..data.len()].copy_from_slice(data);

    let root: Root<'_> = flatbuffers::root::<Root<'_>>(&stack_buf).unwrap();
    let mut foo = root.foo().unwrap();

    loop {
        for _ in 0..4 {
            print!("0x{:016x} ", foo.x());
            foo = foo.inner_foo();
        }
        println!();
    }
}

This code will print the content of the stack and then segfault using only safe rust.

[CasperN]

I think is a general flatbuffers problem -- it does not make sense for a FB struct to be self-referential since they don't support references and would be infinite size. This should have been rejected by the flatc Parser before it got to the Rust code generator. I'd imagine this bug can be replicated in C and possibly elsewhere.

@aardappel

[aardappel]

Yup, the parser should error on this.

[github-actions[bot]]

This issue is stale because it has been open 6 months with no activity. Please comment or label not-stale, or this will be closed in 14 days.

[TethysSvensson]

I don't think this has been fixed.

[github-actions[bot]]

This issue is stale because it has been open 6 months with no activity. Please comment or label not-stale, or this will be closed in 14 days.

[TethysSvensson]

I still don't think this has been fixed.

[github-actions[bot]]

This issue is stale because it has been open 6 months with no activity. Please comment or label not-stale, or this will be closed in 14 days.

[TethysSvensson]

This will still segfault on current master.

[github-actions[bot]]

This issue is stale because it has been open 6 months with no activity. Please comment or label not-stale, or this will be closed in 14 days.

[TethysSvensson]

Nothing has changed, this still causes a segfault in safe rust on current master.