Handle SSH servers that send success response out of spec order

[cabloo]

There are some Juniper switches that have a (maybe incorrect?) implementation of the SSH spec which send back a SUCCESS response at a time this lib does not expect it. This causes the lib to bail out immediately. This patch ensures that when this unexpected SSH response comes back, we just continue operations as usual.

Here's the last bit of the SSH debug output when this behavior was happening:

SSH Error: Error reading channel data (99)

-> NET_SSH2_MSG_REQUEST_FAILURE (since last: 0.0001, network: 0.0001s)
                                                 

<- NET_SSH2_MSG_CHANNEL_OPEN_CONFIRMATION (since last: 0.2641, network: 0s)
00000000  00:00:00:02:00:00:00:00:00:00:00:00:00:00:80:00  ................

-> NET_SSH2_MSG_CHANNEL_REQUEST (since last: 0.0001, network: 0s)
00000000  00:00:00:00:00:00:00:07:70:74:79:2d:72:65:71:01  ........pty-req.
00000010  00:00:00:05:76:74:31:30:30:00:00:03:e8:00:00:00  ....vt100.......
00000020  18:00:00:00:00:00:00:00:00:00:00:00:01:00        ..............

<- NET_SSH2_MSG_CHANNEL_SUCCESS (since last: 0.2727, network: 0s)
00000000  00:00:00:02                                      ....

-> NET_SSH2_MSG_CHANNEL_REQUEST (since last: 0.0001, network: 0s)
00000000  00:00:00:00:00:00:00:05:73:68:65:6c:6c:01        ........shell.

<- NET_SSH2_MSG_CHANNEL_WINDOW_ADJUST (since last: 0.2672, network: 0s)
00000000  00:00:00:02:00:20:00:00                          ..... ..

-> NET_SSH2_MSG_CHANNEL_DATA (since last: 0.0001, network: 0s)
00000000  00:00:00:00:00:00:00:09:0a:0a:0a:0a:0a:0a:0a:0a  ................
00000010  0a                                               .

<- NET_SSH2_MSG_CHANNEL_SUCCESS (since last: 0.0001, network: 0s)
00000000  00:00:00:02                                      ....

-> NET_SSH2_MSG_DISCONNECT (since last: 0, network: 0s)
00000000  00:00:00:0b:00:00:00:00:00:00:00:00              ............


#0 /var/www/html/vendor/phpseclib/phpseclib/phpseclib/Net/SSH2.php(3138): phpseclib3\Net\SSH2->get_channel_packet(2)

[terrafrost]

I'm assuming you're doing $ssh->write("\n\n\n\n\n\n\n\n\n");? Can you post the full SSH2 logs?

In theory phpseclib should request a second binary packet when it encounters a window adjust channel packet:

phpseclib/phpseclib/Net/SSH2.php

Lines 3719 to 3725 in 3e073a5

	case MessageType::CHANNEL_WINDOW_ADJUST:
	Strings::shift($payload, 1);
	list($channel, $window_size) = Strings::unpackSSH2('NN', $payload);
	$this->window_size_client_to_server[$channel] += $window_size;
	$payload = ($this->bitmap & self::MASK_WINDOW_ADJUST) ? true : $this->get_binary_packet($skip_channel_filter);

That's from the filter() method, which is called in get_binary_packet(). The only time $this->bitmap & self::MASK_WINDOW_ADJUST is true is in send_binary_packet():

phpseclib/phpseclib/Net/SSH2.php

Lines 4284 to 4289 in 3e073a5

	if (!$this->window_size_client_to_server[$client_channel]) {
	$this->bitmap ^= self::MASK_WINDOW_ADJUST;
	// using an invalid channel will let the buffers be built up for the valid channels
	$this->get_channel_packet(-1);
	$this->bitmap ^= self::MASK_WINDOW_ADJUST;
	}

Consequently, the change you made shouldn't be necessary. If the code I've mentioned isn't working then that may indicate other problems that this change kinda sweeps under the rug.

[terrafrost]

I'd still love to see log files!

Like I discussed in my last post the concern I have with your PR is that there's already code in place that should deal with the situation you're describing and if that's not working then that's quite potentially a harbinger for other issues that your fix wouldn't address.

Thanks!

[cabloo]

I'm assuming you're doing $ssh->write("\n\n\n\n\n\n\n\n\n");?

That's correct, I do this to determine the host line (the part that gets output when you put a few empty lines in) and differentiate that from the MOTD/any broadcast messages.

Can you post the full SSH2 logs?

Wasn't sure if there was anything sensitive in there, so I've sent via email.

[terrafrost]

I tried to "replay" the logs you gave me without success. That's not exactly an exact science however.

In light of my inability to reproduce them... maybe you could try this?:

#
#-----[ OPEN ]------------------------------------------
#
Net/SSH2.php
#
#-----[ FIND ]------------------------------------------
#
                case NET_SSH2_MSG_CHANNEL_WINDOW_ADJUST:
                    Strings::shift($payload, 1);
                    list($channel, $window_size) = Strings::unpackSSH2('NN', $payload);

                    $this->window_size_client_to_server[$channel] += $window_size;

                    $payload = ($this->bitmap & self::MASK_WINDOW_ADJUST) ? true : $this->get_binary_packet($skip_channel_filter);
#
#-----[ REPLACE WITH ]----------------------------------
#
                case NET_SSH2_MSG_CHANNEL_WINDOW_ADJUST:
echo "THIS FAR\n";
                    Strings::shift($payload, 1);
                    list($channel, $window_size) = Strings::unpackSSH2('NN', $payload);

                    $this->window_size_client_to_server[$channel] += $window_size;

                    $payload = ($this->bitmap & self::MASK_WINDOW_ADJUST) ? true : $this->get_binary_packet($skip_channel_filter);
var_dump($payload);

You can turn off logging and just run it with those changes. They won't fix anything but it'll at least tell me if that block of code is being called. We can proceed from there.

Thanks!

[terrafrost]

Try doing this too:

#
#-----[ OPEN ]------------------------------------------
#
Net/SSH2.php
#
#-----[ FIND ]------------------------------------------
# in initShell
#
        $packet = Strings::packSSH2(
            'CNsb',
            NET_SSH2_MSG_CHANNEL_REQUEST,
            $this->server_channels[self::CHANNEL_SHELL],
            'shell',
            true // want reply
        );
        $this->send_binary_packet($packet);

        $response = $this->get_channel_packet(self::CHANNEL_SHELL);
        if ($response === false) {
            throw new \RuntimeException('Unable to request shell');
        }

        $this->channel_status[self::CHANNEL_SHELL] = NET_SSH2_MSG_CHANNEL_DATA;
#
#-----[ REPLACE WITH ]----------------------------------
#
        $packet = Strings::packSSH2(
            'CNsb',
            NET_SSH2_MSG_CHANNEL_REQUEST,
            $this->server_channels[self::CHANNEL_SHELL],
            'shell',
            true // want reply
        );
        $this->send_binary_packet($packet);
echo "BINARY PACKET SENT\n";

        $response = $this->get_channel_packet(self::CHANNEL_SHELL);
echo "CHANNEL PACKET RCVD\n";
var_dump($response);
        if ($response === false) {
            throw new \RuntimeException('Unable to request shell');
        }

        $this->channel_status[self::CHANNEL_SHELL] = NET_SSH2_MSG_CHANNEL_DATA;