bug: file descriptor leak on z/OS s390x when FcntlInt fails

[pageton]

Description

tcplisten/socket_zos_s390x.go:11-18 leaks the socket file descriptor when FcntlInt fails:

fd, err := unix.Socket(domain, typ, proto)  // succeeds
_, err = unix.FcntlInt(...)                  // overwrites err
_, err = unix.FcntlInt(...)                  // fails
if err == nil {
    return fd, nil
}
return -1, fmt.Errorf(...)  // fd leaked, never closed

Impact

• File descriptor leak on z/OS s390x when FcntlInt fails
• Accumulates over process lifetime on affected platform

Suggested Fix

Close fd before returning the error:

if err != nil {
    unix.Close(fd)
    return -1, fmt.Errorf(...)
}

File

tcplisten/socket_zos_s390x.go:11-18