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Do not invoke accept() on an already-established connection #105

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Do not invoke accept() on an already-established connection #105

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51 changes: 39 additions & 12 deletions varlink/src/server.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -151,6 +151,13 @@ impl Listener {
}
}

pub const fn is_already_accepted(&self) -> bool {
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@cgwalters cgwalters Nov 26, 2024

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While I know the rest of the code is not consistent about this, having at least a minimal documentation string I think is a good idea for public APIs.

match *self {
Self::TCP(_, value) => value,
Self::UNIX(_, value) => value,
}
}

#[cfg(windows)]
pub fn accept(&self, timeout: u64) -> Result<Box<dyn Stream>> {
use winapi::um::winsock2::WSAEINTR as EINTR;
Expand Down Expand Up @@ -194,13 +201,21 @@ impl Listener {
}

match self {
&Listener::TCP(Some(ref l), _) => {
let (s, _addr) = l.accept().map_err(map_context!())?;
Ok(Box::new(s))
&Listener::TCP(Some(ref l), accepted) => {
if accepted {
unsafe { Ok(Box::new(TcpStream::from_raw_fd(l.as_raw_fd()))) }
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@cgwalters cgwalters Nov 26, 2024

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Without digging into this code a lot more, there's a reason those functions are unsafe and that reason is exactly what looks like a bug here: The previous listener still thinks it owns the file descriptor.

We can avoid this by deconstructing into an OwnedFd like Box::new(TcpStream::from(l.into::<OwnedFd>())) or so.

But I think we need to back up on this, I'll comment on the original ticket.

} else {
Comment on lines +205 to +207
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Copilot AI Oct 20, 2025

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Using from_raw_fd() transfers ownership of the file descriptor without validation. This could lead to use-after-free or double-close issues if the original listener is used elsewhere. Consider using a safer approach like cloning the file descriptor with dup() first.

Copilot uses AI. Check for mistakes.
let (s, _addr) = l.accept().map_err(map_context!())?;
Ok(Box::new(s))
}
}
Listener::UNIX(Some(ref l), _) => {
let (s, _addr) = l.accept().map_err(map_context!())?;
Ok(Box::new(s))
Listener::UNIX(Some(ref l), accepted) => {
if *accepted {
unsafe { Ok(Box::new(UnixStream::from_raw_fd(l.as_raw_fd()))) }
Comment on lines +213 to +214
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Copilot AI Oct 20, 2025

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Inconsistent dereferencing pattern: TCP case uses accepted directly while UNIX case uses *accepted. Both should use the same pattern for consistency.

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} else {
let (s, _addr) = l.accept().map_err(map_context!())?;
Ok(Box::new(s))
}
}
_ => Err(context!(ErrorKind::ConnectionClosed)),
}
Expand Down Expand Up @@ -250,13 +265,21 @@ impl Listener {
}
}
match self {
&Listener::TCP(Some(ref l), _) => {
let (s, _addr) = l.accept().map_err(map_context!())?;
Ok(Box::new(s))
&Listener::TCP(Some(ref l), accepted) => {
if accepted {
unsafe { Ok(Box::new(TcpStream::from_raw_fd(l.as_raw_fd()))) }
} else {
Comment on lines +269 to +271
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Copilot AI Oct 20, 2025

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This code is duplicated from the Windows version above (lines 205-210). Consider extracting this logic into a helper method to reduce code duplication.

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let (s, _addr) = l.accept().map_err(map_context!())?;
Ok(Box::new(s))
}
}
Listener::UNIX(Some(ref l), _) => {
let (s, _addr) = l.accept().map_err(map_context!())?;
Ok(Box::new(s))
Listener::UNIX(Some(ref l), accepted) => {
if *accepted {
unsafe { Ok(Box::new(UnixStream::from_raw_fd(l.as_raw_fd()))) }
} else {
Comment on lines +277 to +279
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Copilot AI Oct 20, 2025

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This code is duplicated from both the Windows version and the TCP case above. The same dereferencing inconsistency and duplication issues apply here.

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let (s, _addr) = l.accept().map_err(map_context!())?;
Ok(Box::new(s))
}
}
_ => Err(context!(ErrorKind::ConnectionClosed)),
}
Expand Down Expand Up @@ -607,5 +630,9 @@ pub fn listen<S: ?Sized + AsRef<str>, H: crate::ConnectionHandler + Send + Sync
}
}
});

if listener.is_already_accepted() {
return Ok(());
}
}
}