Preserve inherited target stdin authority

crates/lazaret-linux/tests/acquisition.rs

@@ -1,5 +1,5 @@
 use std::ffi::OsString;
-use std::fs::File;
+use std::fs::{File, OpenOptions};
 use std::io::{Read, Seek, Write};
 use std::os::fd::AsFd;
 use std::process::{ExitCode, Stdio};
@@ -50,6 +50,7 @@ fn run_all() -> std::io::Result<()> {
     successful_acquisition()?;
     transient_captured_child_preserves_streams_and_exit()?;
     terminal_child_restores_slave_stdin_and_merges_output()?;
+    target_stdin_does_not_gain_write_authority()?;
     acknowledged_transition_precedes_exact_wrapper_release()?;
     failed_acknowledged_transition_refuses_exact_wrapper_release()?;
     lifetime_pipe_descriptor_contract()?;
@@ -61,6 +62,54 @@ fn run_all() -> std::io::Result<()> {
     concurrent_acquisitions_serialize()
 }
 
+fn target_stdin_does_not_gain_write_authority() -> std::io::Result<()> {
+    let path = std::env::temp_dir().join(format!(
+        "lazaret-target-stdin-authority-{}-{}",
+        std::process::id(),
+        SEQUENCE.fetch_add(1, Ordering::Relaxed)
+    ));
+    let mut source = OpenOptions::new()
+        .create_new(true)
+        .write(true)
+        .open(&path)?;
+    source.write_all(b"unchanged")?;
+    drop(source);
+    let stdin = OpenOptions::new().read(true).open(&path)?;
+    let target = TargetCommand::new("/bin/sh")
+        .argument("-c")
+        .argument("printf changed >&0")
+        .with_target_stdin(stdin)?;
+    let expected_parent = current_process_identity()?;
+    let ownership = ProcessOwnershipContext {
+        domain_id: DomainId::new([45; 32]),
+        generation_id: GenerationId::new(46),
+        coordinator_id: CoordinatorId::new([47; 32]),
+        slot: HostProcessOwnershipSlot::SessionTerminalExecClient(
+            lazaret_core::identity::SessionId::new([48; 32]),
+        ),
+    };
+    let process = child_broker().acquire_with_stdio(
+        expected_parent,
+        ownership,
+        &target,
+        ChildStandardIo::silenced(),
+        |_| Ok(()),
+        |staged| Ok(ProcessOwnershipCommitAck::v1(staged)),
+    )?;
+    while !process.has_exited()? {
+        std::thread::yield_now();
+    }
+    let exit = child_broker().reap_status(process)?;
+    let contents = std::fs::read(&path);
+    let _ = std::fs::remove_file(&path);
+    if exit.exit_code == Some(0) || contents? != b"unchanged" {
+        return Err(std::io::Error::other(format!(
+            "read-only target stdin gained write authority: {exit:?}"
+        )));
+    }
+    Ok(())
+}
+
 fn terminal_child_restores_slave_stdin_and_merges_output() -> std::io::Result<()> {
     let master = openpt(OpenptFlags::RDWR | OpenptFlags::NOCTTY | OpenptFlags::CLOEXEC)?;
     grantpt(&master)?;