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refactor channels.c

Move static state to a "struct ssh_channels" that is allocated at
runtime and tracked as a member of struct ssh.

Explicitly pass "struct ssh" to all channels functions.

Replace use of the legacy packet APIs in channels.c.

Rework sshd_config PermitOpen handling: previously the configuration
parser would call directly into the channels layer. After the refactor
this is not possible, as the channels structures are allocated at
connection time and aren't available when the configuration is parsed.
The server config parser now tracks PermitOpen itself and explicitly
configures the channels code later.

ok markus@

/* $OpenBSD: nchan.c,v 1.66 2017/09/12 06:32:07 djm Exp $ */
/*
 * Copyright (c) 1999, 2000, 2001, 2002 Markus Friedl.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include <sys/types.h>
#include <sys/socket.h>
#include <sys/queue.h>

#include <errno.h>
#include <string.h>
#include <stdarg.h>

#include "ssh2.h"
#include "sshbuf.h"
#include "ssherr.h"
#include "packet.h"
#include "channels.h"
#include "compat.h"
#include "log.h"

/*
 * SSH Protocol 1.5 aka New Channel Protocol
 * Thanks to Martina, Axel and everyone who left Erlangen, leaving me bored.
 * Written by Markus Friedl in October 1999
 *
 * Protocol versions 1.3 and 1.5 differ in the handshake protocol used for the
 * tear down of channels:
 *
 * 1.3:	strict request-ack-protocol:
 *	CLOSE	->
 *		<-  CLOSE_CONFIRM
 *
 * 1.5:	uses variations of:
 *	IEOF	->
 *		<-  OCLOSE
 *		<-  IEOF
 *	OCLOSE	->
 *	i.e. both sides have to close the channel
 *
 * 2.0: the EOF messages are optional
 *
 * See the debugging output from 'ssh -v' and 'sshd -d' of
 * ssh-1.2.27 as an example.
 *
 */

/* functions manipulating channel states */
/*
 * EVENTS update channel input/output states execute ACTIONS
 */
/*
 * ACTIONS: should never update the channel states
 */
static void	chan_send_eof2(struct ssh *, Channel *);
static void	chan_send_eow2(struct ssh *, Channel *);

/* helper */
static void	chan_shutdown_write(struct ssh *, Channel *);
static void	chan_shutdown_read(struct ssh *, Channel *);

static const char *ostates[] = { "open", "drain", "wait_ieof", "closed" };
static const char *istates[] = { "open", "drain", "wait_oclose", "closed" };

static void
chan_set_istate(Channel *c, u_int next)
{
	if (c->istate > CHAN_INPUT_CLOSED || next > CHAN_INPUT_CLOSED)
		fatal("chan_set_istate: bad state %d -> %d", c->istate, next);
	debug2("channel %d: input %s -> %s", c->self, istates[c->istate],
	    istates[next]);
	c->istate = next;
}

static void
chan_set_ostate(Channel *c, u_int next)
{
	if (c->ostate > CHAN_OUTPUT_CLOSED || next > CHAN_OUTPUT_CLOSED)
		fatal("chan_set_ostate: bad state %d -> %d", c->ostate, next);
	debug2("channel %d: output %s -> %s", c->self, ostates[c->ostate],
	    ostates[next]);
	c->ostate = next;
}

void
chan_read_failed(struct ssh *ssh, Channel *c)
{
	debug2("channel %d: read failed", c->self);
	switch (c->istate) {
	case CHAN_INPUT_OPEN:
		chan_shutdown_read(ssh, c);
		chan_set_istate(c, CHAN_INPUT_WAIT_DRAIN);
		break;
	default:
		error("channel %d: chan_read_failed for istate %d",
		    c->self, c->istate);
		break;
	}
}

void
chan_ibuf_empty(struct ssh *ssh, Channel *c)
{
	debug2("channel %d: ibuf empty", c->self);
	if (sshbuf_len(c->input)) {
		error("channel %d: chan_ibuf_empty for non empty buffer",
		    c->self);
		return;
	}
	switch (c->istate) {
	case CHAN_INPUT_WAIT_DRAIN:
		if (!(c->flags & (CHAN_CLOSE_SENT|CHAN_LOCAL)))
			chan_send_eof2(ssh, c);
		chan_set_istate(c, CHAN_INPUT_CLOSED);
		break;
	default:
		error("channel %d: chan_ibuf_empty for istate %d",
		    c->self, c->istate);
		break;
	}
}

void
chan_obuf_empty(struct ssh *ssh, Channel *c)
{
	debug2("channel %d: obuf empty", c->self);
	if (sshbuf_len(c->output)) {
		error("channel %d: chan_obuf_empty for non empty buffer",
		    c->self);
		return;
	}
	switch (c->ostate) {
	case CHAN_OUTPUT_WAIT_DRAIN:
		chan_shutdown_write(ssh, c);
		chan_set_ostate(c, CHAN_OUTPUT_CLOSED);
		break;
	default:
		error("channel %d: internal error: obuf_empty for ostate %d",
		    c->self, c->ostate);
		break;
	}
}

void
chan_rcvd_eow(struct ssh *ssh, Channel *c)
{
	debug2("channel %d: rcvd eow", c->self);
	switch (c->istate) {
	case CHAN_INPUT_OPEN:
		chan_shutdown_read(ssh, c);
		chan_set_istate(c, CHAN_INPUT_CLOSED);
		break;
	}
}

static void
chan_send_eof2(struct ssh *ssh, Channel *c)
{
	int r;

	debug2("channel %d: send eof", c->self);
	switch (c->istate) {
	case CHAN_INPUT_WAIT_DRAIN:
		if ((r = sshpkt_start(ssh, SSH2_MSG_CHANNEL_EOF)) != 0 ||
		    (r = sshpkt_put_u32(ssh, c->remote_id)) != 0 ||
		    (r = sshpkt_send(ssh)) != 0)
			fatal("%s: send CHANNEL_EOF: %s", __func__, ssh_err(r));
		c->flags |= CHAN_EOF_SENT;
		break;
	default:
		error("channel %d: cannot send eof for istate %d",
		    c->self, c->istate);
		break;
	}
}

static void
chan_send_close2(struct ssh *ssh, Channel *c)
{
	int r;

	debug2("channel %d: send close", c->self);
	if (c->ostate != CHAN_OUTPUT_CLOSED ||
	    c->istate != CHAN_INPUT_CLOSED) {
		error("channel %d: cannot send close for istate/ostate %d/%d",
		    c->self, c->istate, c->ostate);
	} else if (c->flags & CHAN_CLOSE_SENT) {
		error("channel %d: already sent close", c->self);
	} else {
		if ((r = sshpkt_start(ssh, SSH2_MSG_CHANNEL_CLOSE)) != 0 ||
		    (r = sshpkt_put_u32(ssh, c->remote_id)) != 0 ||
		    (r = sshpkt_send(ssh)) != 0)
			fatal("%s: send CHANNEL_EOF: %s", __func__, ssh_err(r));
		c->flags |= CHAN_CLOSE_SENT;
	}
}

static void
chan_send_eow2(struct ssh *ssh, Channel *c)
{
	int r;

	debug2("channel %d: send eow", c->self);
	if (c->ostate == CHAN_OUTPUT_CLOSED) {
		error("channel %d: must not sent eow on closed output",
		    c->self);
		return;
	}
	if (!(datafellows & SSH_NEW_OPENSSH))
		return;
	if ((r = sshpkt_start(ssh, SSH2_MSG_CHANNEL_REQUEST)) != 0 ||
	    (r = sshpkt_put_u32(ssh, c->remote_id)) != 0 ||
	    (r = sshpkt_put_cstring(ssh, "eow@openssh.com")) != 0 ||
	    (r = sshpkt_put_u8(ssh, 0)) != 0 ||
	    (r = sshpkt_send(ssh)) != 0)
		fatal("%s: send CHANNEL_EOF: %s", __func__, ssh_err(r));
}

/* shared */

void
chan_rcvd_ieof(struct ssh *ssh, Channel *c)
{
	debug2("channel %d: rcvd eof", c->self);
	c->flags |= CHAN_EOF_RCVD;
	if (c->ostate == CHAN_OUTPUT_OPEN)
		chan_set_ostate(c, CHAN_OUTPUT_WAIT_DRAIN);
	if (c->ostate == CHAN_OUTPUT_WAIT_DRAIN &&
	    sshbuf_len(c->output) == 0 &&
	    !CHANNEL_EFD_OUTPUT_ACTIVE(c))
		chan_obuf_empty(ssh, c);
}

void
chan_rcvd_oclose(struct ssh *ssh, Channel *c)
{
	debug2("channel %d: rcvd close", c->self);
	if (!(c->flags & CHAN_LOCAL)) {
		if (c->flags & CHAN_CLOSE_RCVD)
			error("channel %d: protocol error: close rcvd twice",
			    c->self);
		c->flags |= CHAN_CLOSE_RCVD;
	}
	if (c->type == SSH_CHANNEL_LARVAL) {
		/* tear down larval channels immediately */
		chan_set_ostate(c, CHAN_OUTPUT_CLOSED);
		chan_set_istate(c, CHAN_INPUT_CLOSED);
		return;
	}
	switch (c->ostate) {
	case CHAN_OUTPUT_OPEN:
		/*
		 * wait until a data from the channel is consumed if a CLOSE
		 * is received
		 */
		chan_set_ostate(c, CHAN_OUTPUT_WAIT_DRAIN);
		break;
	}
	switch (c->istate) {
	case CHAN_INPUT_OPEN:
		chan_shutdown_read(ssh, c);
		chan_set_istate(c, CHAN_INPUT_CLOSED);
		break;
	case CHAN_INPUT_WAIT_DRAIN:
		if (!(c->flags & CHAN_LOCAL))
			chan_send_eof2(ssh, c);
		chan_set_istate(c, CHAN_INPUT_CLOSED);
		break;
	}
}

void
chan_write_failed(struct ssh *ssh, Channel *c)
{
	debug2("channel %d: write failed", c->self);
	switch (c->ostate) {
	case CHAN_OUTPUT_OPEN:
	case CHAN_OUTPUT_WAIT_DRAIN:
		chan_shutdown_write(ssh, c);
		if (strcmp(c->ctype, "session") == 0)
			chan_send_eow2(ssh, c);
		chan_set_ostate(c, CHAN_OUTPUT_CLOSED);
		break;
	default:
		error("channel %d: chan_write_failed for ostate %d",
		    c->self, c->ostate);
		break;
	}
}

void
chan_mark_dead(struct ssh *ssh, Channel *c)
{
	c->type = SSH_CHANNEL_ZOMBIE;
}

int
chan_is_dead(struct ssh *ssh, Channel *c, int do_send)
{
	if (c->type == SSH_CHANNEL_ZOMBIE) {
		debug2("channel %d: zombie", c->self);
		return 1;
	}
	if (c->istate != CHAN_INPUT_CLOSED || c->ostate != CHAN_OUTPUT_CLOSED)
		return 0;
	if ((datafellows & SSH_BUG_EXTEOF) &&
	    c->extended_usage == CHAN_EXTENDED_WRITE &&
	    c->efd != -1 &&
	    sshbuf_len(c->extended) > 0) {
		debug2("channel %d: active efd: %d len %zu",
		    c->self, c->efd, sshbuf_len(c->extended));
		return 0;
	}
	if (c->flags & CHAN_LOCAL) {
		debug2("channel %d: is dead (local)", c->self);
		return 1;
	}		
	if (!(c->flags & CHAN_CLOSE_SENT)) {
		if (do_send) {
			chan_send_close2(ssh, c);
		} else {
			/* channel would be dead if we sent a close */
			if (c->flags & CHAN_CLOSE_RCVD) {
				debug2("channel %d: almost dead",
				    c->self);
				return 1;
			}
		}
	}
	if ((c->flags & CHAN_CLOSE_SENT) &&
	    (c->flags & CHAN_CLOSE_RCVD)) {
		debug2("channel %d: is dead", c->self);
		return 1;
	}
	return 0;
}

/* helper */
static void
chan_shutdown_write(struct ssh *ssh, Channel *c)
{
	sshbuf_reset(c->output);
	if (c->type == SSH_CHANNEL_LARVAL)
		return;
	/* shutdown failure is allowed if write failed already */
	debug2("channel %d: close_write", c->self);
	if (c->sock != -1) {
		if (shutdown(c->sock, SHUT_WR) < 0)
			debug2("channel %d: chan_shutdown_write: "
			    "shutdown() failed for fd %d: %.100s",
			    c->self, c->sock, strerror(errno));
	} else {
		if (channel_close_fd(ssh, &c->wfd) < 0)
			logit("channel %d: chan_shutdown_write: "
			    "close() failed for fd %d: %.100s",
			    c->self, c->wfd, strerror(errno));
	}
}

static void
chan_shutdown_read(struct ssh *ssh, Channel *c)
{
	if (c->type == SSH_CHANNEL_LARVAL)
		return;
	debug2("channel %d: close_read", c->self);
	if (c->sock != -1) {
		if (shutdown(c->sock, SHUT_RD) < 0)
			error("channel %d: chan_shutdown_read: "
			    "shutdown() failed for fd %d [i%d o%d]: %.100s",
			    c->self, c->sock, c->istate, c->ostate,
			    strerror(errno));
	} else {
		if (channel_close_fd(ssh, &c->rfd) < 0)
			logit("channel %d: chan_shutdown_read: "
			    "close() failed for fd %d: %.100s",
			    c->self, c->rfd, strerror(errno));
	}
}