`SockaddrStorage` broken for variable-length addresses

[stevenengler]

The SockaddrStorage type "forgets" the address length, which causes incorrect and unexpected behaviour. I think this is a more fundamental issue with how nix represents socket addresses.

Example:

use std::os::unix::io::AsRawFd;
use std::os::unix::net::UnixListener;

use nix::sys::socket::{connect, getsockname, socket};
use nix::sys::socket::{AddressFamily, SockFlag, SockType, SockaddrStorage};

let listener = UnixListener::bind("/tmp/example.sock").unwrap();
let listener_fd = listener.as_raw_fd();
let listener_addr: SockaddrStorage = getsockname(listener_fd).unwrap();

let peer_fd = socket(AddressFamily::Unix, SockType::Stream, SockFlag::empty(), None).unwrap();

// this panics
connect(peer_fd, &listener_addr).unwrap();

If we look at the strace, we can see that nix is proving the wrong sockaddr length to connect(), which represents an incorrect address. This is equally important for abstract named and unnamed unix sockets.

socket(AF_UNIX, SOCK_STREAM|SOCK_CLOEXEC, 0) = 3
bind(3, {sa_family=AF_UNIX, sun_path="/tmp/example.sock"}, 20) = 0
listen(3, 4294967295)                   = 0
getsockname(3, {sa_family=AF_UNIX, sun_path="/tmp/example.sock"}, [128->20]) = 0
write(1, "SockaddrStorage { ss: sockaddr_s"..., 91SockaddrStorage { ss: sockaddr_storage { ss_family: 1, __ss_align: 8299682679707492728 } }
) = 91
socket(AF_UNIX, SOCK_STREAM, 0)         = 4
connect(4, {sa_family=AF_UNIX, sun_path="/tmp/example.sock"}, 128) = -1 EINVAL (Invalid argument)

When you're writing code that has to support many different socket address types, this means that SockaddrStorage is unusable. We're currently sticking with the deprecated nix::sys::socket::SockAddr for now as it doesn't have this issue.

[asomers]

I see. This isn't a problem on BSDs, where sockaddr_storage does know its own size. That's probably why I never noticed this before, because that's where I do most of my development. UnixAddr already has a workaround for Linux-like OSes, and a similar workaround is probably needed for SockaddrStorage. As far as you know, is the problem limited to Unix-domain socket addresses?

[stevenengler]

I see. This isn't a problem on BSDs, where sockaddr_storage does know its own size. That's probably why I never noticed this before, because that's where I do most of my development. UnixAddr already has a workaround for Linux-like OSes, and a similar workaround is probably needed for SockaddrStorage.

Unfortunately I have no experience with any BSDs, so I can see how it's a pain trying to abstract around both socket address implementations.

As far as you know, is the problem limited to Unix-domain socket addresses?

I think so, I don't know of any other variable-length socket addresses on Linux, but there are a lot of protocol families I've never used.