Hello 🦀 , we (Rust group @sslab-gatech) found an undefined-behavior issue in this crate while scanning Rust code on crates.io for potential vulnerabilities.

Issue

Send is unconditionally implemented for Demuxer, so that it is possible for a non-Send implementor of DemuxerEvents trait to be sent across thread boundaries.

unsafe impl<T> Send for Demuxer<T> where T: DemuxerEvents {}

Proof of Concept

Here is a simple program where Demuxer is used to move a MutexGuard(!Send object) to another thread.
It is also possible to create data races by inserting non-Send types like Rc or Cell into Demuxer
(which is not demonstrated in the example code below).

use va_ts::{Demuxer, DemuxerEvents, SubtableID, DemuxedPacket, DemuxedTable};
use std::sync::{Mutex, MutexGuard};
use std::thread::{self, ThreadId};
use std::ops::Drop;

struct X(MutexGuard<'static, u64>, ThreadId);
impl DemuxerEvents for X {
    fn on_table(&mut self, _: SubtableID, _: &DemuxedTable) { }
    fn on_packet(&mut self, _: &DemuxedPacket) { }
}
impl Drop for X {
    fn drop(&mut self) {
        // `MutexGuard` must not be dropped from a thread that didn't lock the `Mutex`.
        //
        // If a thread attempts to unlock a Mutex that it has not locked, it can result in undefined behavior.
        // (https://github.com/rust-lang/rust/issues/23465#issuecomment-82730326)
        assert_eq!(self.1, thread::current().id());
    }
}

fn main() {
    let static_mutex = Box::leak(Box::new(Mutex::new(0xbeefbeef_u64)));
    // MutexGuard is `!Send`
    let mutex_guard = static_mutex.lock().unwrap();
    let tid = thread::current().id();

    let demuxer = Demuxer::new(X(mutex_guard, tid));
    std::thread::spawn(move || {
        let demuxer = demuxer;

        // demuxer is dropped here, along with `MutexGuard`.
    }).join().unwrap();
}

Suggested Fix

Adding a trait bound T: Send as below will allow the compiler to prevent Demuxer from moving !Send types across thread boundaries.

unsafe impl<T> Send for Demuxer<T> where T: DemuxerEvents + Send {}

Thank you for reviewing this issue 👍

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Open

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• Update Rust crate clap to ~4.5.0

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Howdy,
Not sure if any of the MPEGTS muxing is working from what I can see in the code?
If so, and I'm missing something, do you have a working example of muxing video, audio and producing the SI tables into the TS stream?
Can the muxer operating via fifo's and not rely an files as input and output?

Cheers