The order in which tinc initialized things was not completely correct. Now, it
is done as follows:
- Load and parse configuration files.
- Create all TCP and UDP listening sockets.
- Create PID file and UNIX socket.
- Run the tinc-up script.
- Drop privileges.
- Start outgoing connections.
- Run the main loop.
The PID file can only be created correctly if the listening sockets have been
set up ,as it includes the address and port of the first listening socket. The
tinc-up script has to be run after the PID file and UNIX socket have been
created so it can change their permissions if necessary. Outgoing connections
should only be started right before the main loop, because this is not really
part of the initialization.
The PID file was created before tinc-up was called, but the UNIX socket was
created afterwards, which meant one could not change the UNIX socket's owner or
permissions from the tinc-up script.
As mentioned by Erik Tews, calling fchmod() after fopen() leaves a small window
for exploits. As long as tinc is single-threaded, we can use umask() instead to
reduce file permissions. This also works when creating the AF_UNIX control socket.
The umask of the user running tinc(d) is used for most files, except for the
private keys, invitation files, PID file and control socket.
There are several reasons for this:
- MacOS/X doesn't support polling the tap device using kqueue, requiring a
workaround to fall back to select().
- On Windows only sockets are properly handled, therefore tinc uses a second
thread that does a blocking ReadFile() on the TAP-Win32/64 device. However,
this does not mix well with libevent.
- Libevent, event just the core, is quite large, and although it is easy to get
and install on many platforms, it can be a burden.
- Libev is more lightweight and seems technically superior, but it doesn't
abstract away all the platform differences (for example, async events are not
supported on Windows).
The tree functions were never used on the connection_tree, a list is more appropriate.
Also be more paranoid about connections disappearing while traversing the list.
This allows tincctl to receive log messages from a running tincd,
independent of what is logged to syslog or to file. Tincctl can receive
debug messages with an arbitrary level.
The pid is now written first, so that a version 1.0.x tincd can be used to stop
a running version 1.1 tincd. Getsockname() is used to determine the address of
the first listening socket, so that tincctl can connect to the local tincd even
if AddressFamily = ipv6, or if BindToAddress or BindToInterface is used.
The control socket code was completely different from how meta connections are
handled, resulting in lots of extra code to handle requests. Also, not every
operating system has UNIX sockets, so we have to resort to another type of
sockets or pipes for those anyway. To reduce code duplication and make control
sockets work the same on all platforms, we now just connect to the TCP port
where tincd is already listening on.
To authenticate, the program that wants to control a running tinc daemon must
send the contents of a cookie file. The cookie is a random 256 bits number that
is regenerated every time tincd starts. The cookie file should only be readable
by the same user that can start a tincd.
Instead of the binary-ish protocol previously used, we now use an ASCII
protocol similar to that of the meta connections, but this can still change.
UNIX domain sockets, of course, don't exist on Windows. For now, when compiling
tinc in a MinGW environment, try to use a TCP socket bound to localhost as an
alternative.
This provides reasonable security even on Solaris. The sysadmin is
responsible for securing the control socket's ancestors from the
grandparent on.
We could add a cryptographic handshake later if desired.
