fd_advise on invalid file descriptors report ok

[yagehu]

Describe the bug

Calling fd_advise on a clearly invalid file descriptor returns 0 in all conditions.

Minimal Rust repro:

use wasi::ADVICE_WILLNEED;

fn main() {
    unsafe {
        let result = wasi::fd_advise(6, 0, 0, ADVICE_WILLNEED);

        match result {
            Ok(()) => eprintln!("fd_advise ok"),
            Err(errno) => eprintln!("fd_advise failed with {errno}"),
        }
    }
}

$ cargo build --target wasm32-wasi

$ wasmer -vV; rustc -vV
wasmer 4.2.5 (0460050 2024-03-05)
binary: wasmer-cli
commit-hash: 04600507844bae978239531c8e6265d410aefe6d
commit-date: 2024-03-05
host: x86_64-unknown-linux-gnu
compiler: singlepass,cranelift
rustc 1.77.1 (7cf61ebde 2024-03-27)
binary: rustc
commit-hash: 7cf61ebde7b22796c69757901dd346d0fe70bd97
commit-date: 2024-03-27
host: x86_64-unknown-linux-gnu
release: 1.77.1
LLVM version: 17.0.6

Steps to reproduce

Run the above Rust snippet compiled to wasm32-wasi. It should output fd_advise failed with <errno>, but it reports fd_advise ok.

Expected behavior

When the fd is invalid, like a random or very large number, fd_advise should report something like ebadf.

Actual behavior

fd_advise returns ok (0) in all cases.

Additional context

This was uncovered in differential fuzzing between Wasmer and other Wasm/WASI runtimes. I have a simple PR to fix this behavior.