main: Avoid infinite "303 See Other" loops on certificate-only authgroups

Since we are now caching the authgroup selection, it is possible to
receive a form from the server that skips all user prompts.  If the
selected authgroup is set up for certificate auth only (no l/p) and the
client certificate is not valid, the server will render a new form which
shows only the authgroup dropdown.  Since our CLI caches this response,
we need to make sure it doesn't keep resubmitting the same response over
and over again.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
library: Bump API version to 2.3 and document changes

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
Unconditionally redirect CSD stdout to stderr

CSD output breaks --cookieonly, so let's make a rule that
openconnect_obtain_cookie() will never print to stdout.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
dtls: Don't send packets to a dead socket during rekeying

vpninfo->{dtls_fd,dtls_ssl} are typically invalid when dtls_restart()
returns, as the new handshake has not completed at that point.  Under some
circumstances, FD_CLR() may be called on a negative fd, resulting in a
crash:

    (gdb) bt
    #0  0x00007f749201df77 in __GI_raise (sig=sig@entry=6)
        at ../nptl/sysdeps/unix/sysv/linux/raise.c:56
    #1  0x00007f74920215e8 in __GI_abort () at abort.c:90
    #2  0x00007f749205b4fb in __libc_message (do_abort=do_abort@entry=2,
        fmt=fmt@entry=0x7f749216cf10 "*** %s ***: %s terminated\n")
        at ../sysdeps/unix/sysv/linux/libc_fatal.c:199
    #3  0x00007f74920f908c in __GI___fortify_fail (msg=<optimized out>,
        msg@entry=0x7f749216cea7 "buffer overflow detected") at fortify_fail.c:37
    #4  0x00007f74920f8020 in __GI___chk_fail () at chk_fail.c:28
    #5  0x00007f74920f8fd7 in __fdelt_chk (d=<optimized out>) at fdelt_chk.c:25
    #6  0x00007f749388b86c in ?? ()
    #7  0x00007f749388e271 in ?? ()
    #8  0x00007f74938883a2 in ?? ()
    #9  0x00007f7492008de5 in __libc_start_main (main=0x7f7493887010, argc=5,
        ubp_av=0x7fff01f1fe98, init=<optimized out>, fini=<optimized out>,
        rtld_fini=<optimized out>, stack_end=0x7fff01f1fe88) at libc-start.c:260
    #10 0x00007f74938885e3 in ?? ()

So we should return back to the mainloop instead of trying to send out
queued packets over DTLS.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
main: --cookie-on-stdin doesn't work with ocserv cookies

ocserv's cookie strings are typically much longer (512 characters) than
the cookies generated by a Cisco ASA (<100 characters).  So when
network-manager-openconnect tries to connect to ocserv, the connection
will abruptly drop, and this will show up in syslog:

    NetworkManager[717]: <info> VPN plugin state changed: starting (3)
    NetworkManager[717]: <info> VPN connection 'ocserv' (Connect) reply received.
    openconnect[23054]: Attempting to connect to server 192.168.0.1:443
    openconnect[23054]: SSL negotiation with 192.168.0.1
    openconnect[23054]: Connected to HTTPS on 192.168.0.1
    openconnect[23054]: VPN service unavailable; reason: <unknown>

Quick fix is to allow up to 1024 bytes + NUL termination for the cookie
string.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
ssl: Set FD_CLOEXEC on all sockets

It was recently discovered that open CSTP sockets were being inherited
by the tunnel script.  Use FD_CLOEXEC so this no longer happens.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
www: Fix quoting in v5.01 changelog

Using "&lt;" instead of "&amp;lt", the entry renders as "Attempt to
handle in aggregate auth mode."  Which does not make any sense.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
www: Update changelog

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
gnutls: Remove unused local variable

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
Introduce new helper functions for cancel_fd checking

The same code shows up in 12 places, so we'll move it into a common
location.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
library: Rename cancel_fd to cmd_fd

Applications which use libopenconnect may need to interrupt the mainloop
for a couple of reasons:

 - Cancel/disconnect
 - Force reconnect: in case the IP configuration changed
 - Retrieving bytecounts or other internal information

The cancel_fd mechanism provides a convenient way to send these commands,
but first we need to make it more generic (while preserving backward
compatibility).

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
library: Add new openconnect_setup_cmd_pipe() call

Most callers will use a simple nonblocking UNIX pipe as their cmd_fd,
so provide a convenience function for creating it.  Also, libopenconnect
will take care of cleaning up pipes created in this manner when the
library instance is freed.

Pipes created through this function will be able to send new commands,
such as "reconnect".  Pipes passed in via openconnect_set_cancel_fd()
can only be used to cancel the connection, for backward compatibility.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
Add new helper functions to support cmd_fd feature

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
Move signal handling out of mainloop

In order to make the mainloop a reusable library function, it should not
take over any POSIX signals.  Handle the signals in main.c instead, and
use the cmd_fd mechanism to tell the mainloop to exit.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
mainloop: Convert vpn_mainloop() into a library function

Rename to openconnect_mainloop() and allow the caller to specify
reconnection parameters.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
dtls: Add dtls_close() helper function

This provides an easy way to clean up or shut down DTLS.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
mainloop: Add OC_CMD_PAUSE operation

This forces the connection to immediately drop, and
openconnect_mainloop() to return with status 1.  The caller may
re-invoke the mainloop when he wants to re-establish the connection,
assuming the idle/session timeouts have not expired.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
main: Introduce xstrdup() function

This will abort on error, instead of causing a segfault.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
tun: Export setup_tun() functionality

Create three new setup_tun() library functions:

    openconnect_setup_tun_device - create a tun device
    openconnect_setup_tun_script - pass traffic through a script
    openconnect_setup_tun_fd - pass traffic through an existing fd

The latter is needed to support Android's VpnService API.

In all cases, the caller no longer needs to directly manipulate
vpninfo->vpnc_script or vpninfo->script_tun.  The former is treated as
a standard caller-allocated, library-freed string.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
Move vpninfo default settings into library

This allows main.c to call openconnect_vpninfo_new() to create the
library instance.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>