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putty/sshshare.c

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C
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/*
* Support for SSH connection sharing, i.e. permitting one PuTTY to
* open its own channels over the SSH session being run by another.
*/
/*
* Discussion and technical documentation
* ======================================
*
* The basic strategy for PuTTY's implementation of SSH connection
* sharing is to have a single 'upstream' PuTTY process, which manages
* the real SSH connection and all the cryptography, and then zero or
* more 'downstream' PuTTYs, which never talk to the real host but
* only talk to the upstream through local IPC (Unix-domain sockets or
* Windows named pipes).
*
* The downstreams communicate with the upstream using a protocol
* derived from SSH itself, which I'll document in detail below. In
* brief, though: the downstream->upstream protocol uses a trivial
* binary packet protocol (just length/type/data) to encapsulate
* unencrypted SSH messages, and downstreams talk to the upstream more
* or less as if it was an SSH server itself. (So downstreams can
* themselves open multiple SSH channels, for example, by sending
* multiple SSH2_MSG_CHANNEL_OPENs; they can send CHANNEL_REQUESTs of
* their choice within each channel, and they handle their own
* WINDOW_ADJUST messages.)
*
* The upstream would ideally handle these downstreams by just putting
* their messages into the queue for proper SSH-2 encapsulation and
* encryption and sending them straight on to the server. However,
* that's not quite feasible as written, because client-side channel
* IDs could easily conflict (between multiple downstreams, or between
* a downstream and the upstream). To protect against that, the
* upstream rewrites the client-side channel IDs in messages it passes
* on to the server, so that it's performing what you might describe
* as 'channel-number NAT'. Then the upstream remembers which of its
* own channel IDs are channels it's managing itself, and which are
* placeholders associated with a particular downstream, so that when
* replies come in from the server they can be sent on to the relevant
* downstream (after un-NATting the channel number, of course).
*
* Global requests from downstreams are only accepted if the upstream
* knows what to do about them; currently the only such requests are
* the ones having to do with remote-to-local port forwarding (in
* which, again, the upstream remembers that some of the forwardings
* it's asked the server to set up were on behalf of particular
* downstreams, and sends the incoming CHANNEL_OPENs to those
* downstreams when connections come in).
*
* Other fiddly pieces of this mechanism are X forwarding and
* (OpenSSH-style) agent forwarding. Both of these have a fundamental
* problem arising from the protocol design: that the CHANNEL_OPEN
* from the server introducing a forwarded connection does not carry
* any indication of which session channel gave rise to it; so if
* session channels from multiple downstreams enable those forwarding
* methods, it's hard for the upstream to know which downstream to
* send the resulting connections back to.
*
* For X forwarding, we can work around this in a really painful way
* by using the fake X11 authorisation data sent to the server as part
* of the forwarding setup: upstream ensures that every X forwarding
* request carries distinguishable fake auth data, and then when X
* connections come in it waits to see the auth data in the X11 setup
* message before it decides which downstream to pass the connection
* on to.
*
* For agent forwarding, that workaround is unavailable. As a result,
* this system (and, as far as I can think of, any other system too)
* has the fundamental constraint that it can only forward one SSH
* agent - it can't forward two agents to different session channels.
* So downstreams can request agent forwarding if they like, but if
* they do, they'll get whatever SSH agent is known to the upstream
* (if any) forwarded to their sessions.
*
* Downstream-to-upstream protocol
* -------------------------------
*
* Here I document in detail the protocol spoken between PuTTY
* downstreams and upstreams over local IPC. The IPC mechanism can
* vary between host platforms, but the protocol is the same.
*
* The protocol commences with a version exchange which is exactly
* like the SSH-2 one, in that each side sends a single line of text
* of the form
*
* <protocol>-<version>-<softwareversion> [comments] \r\n
*
* The only difference is that in real SSH-2, <protocol> is the string
* "SSH", whereas in this protocol the string is
* "SSHCONNECTION@putty.projects.tartarus.org".
*
* (The SSH RFCs allow many protocol-level identifier namespaces to be
* extended by implementors without central standardisation as long as
* they suffix "@" and a domain name they control to their new ids.
* RFC 4253 does not define this particular name to be changeable at
* all, but I like to think this is obviously how it would have done
* so if the working group had foreseen the need :-)
*
* Thereafter, all data exchanged consists of a sequence of binary
* packets concatenated end-to-end, each of which is of the form
*
* uint32 length of packet, N
* byte[N] N bytes of packet data
*
* and, since these are SSH-2 messages, the first data byte is taken
* to be the packet type code.
*
* These messages are interpreted as those of an SSH connection, after
* userauth completes, and without any repeat key exchange.
* Specifically, any message from the SSH Connection Protocol is
* permitted, and also SSH_MSG_IGNORE, SSH_MSG_DEBUG,
* SSH_MSG_DISCONNECT and SSH_MSG_UNIMPLEMENTED from the SSH Transport
* Protocol.
*
* This protocol imposes a few additional requirements, over and above
* those of the standard SSH Connection Protocol:
*
* Message sizes are not permitted to exceed 0x4010 (16400) bytes,
* including their length header.
*
* When the server (i.e. really the PuTTY upstream) sends
* SSH_MSG_CHANNEL_OPEN with channel type "x11", and the client
* (downstream) responds with SSH_MSG_CHANNEL_OPEN_CONFIRMATION, that
* confirmation message MUST include an initial window size of at
* least 256. (Rationale: this is a bit of a fudge which makes it
* easier, by eliminating the possibility of nasty edge cases, for an
* upstream to arrange not to pass the CHANNEL_OPEN on to downstream
* until after it's seen the X11 auth data to decide which downstream
* it needs to go to.)
*/
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <limits.h>
#include "putty.h"
#include "tree234.h"
#include "ssh.h"
struct ssh_sharing_state {
const struct plug_function_table *fn;
/* the above variable absolutely *must* be the first in this structure */
char *sockname; /* the socket name, kept for cleanup */
Socket listensock; /* the master listening Socket */
tree234 *connections; /* holds ssh_sharing_connstates */
unsigned nextid; /* preferred id for next connstate */
Ssh ssh; /* instance of the ssh backend */
char *server_verstring; /* server version string after "SSH-" */
};
struct share_globreq;
struct ssh_sharing_connstate {
const struct plug_function_table *fn;
/* the above variable absolutely *must* be the first in this structure */
unsigned id; /* used to identify this downstream in log messages */
Socket sock; /* the Socket for this connection */
struct ssh_sharing_state *parent;
int crLine; /* coroutine state for share_receive */
int sent_verstring, got_verstring, curr_packetlen;
unsigned char recvbuf[0x4010];
int recvlen;
/*
* Assorted state we have to remember about this downstream, so
* that we can clean it up appropriately when the downstream goes
* away.
*/
/* Channels which don't have a downstream id, i.e. we've passed a
* CHANNEL_OPEN down from the server but not had an
* OPEN_CONFIRMATION or OPEN_FAILURE back. If downstream goes
* away, we respond to all of these with OPEN_FAILURE. */
tree234 *halfchannels; /* stores 'struct share_halfchannel' */
/* Channels which do have a downstream id. We need to index these
* by both server id and upstream id, so we can find a channel
* when handling either an upward or a downward message referring
* to it. */
tree234 *channels_by_us; /* stores 'struct share_channel' */
tree234 *channels_by_server; /* stores 'struct share_channel' */
/* Another class of channel which doesn't have a downstream id.
* The difference between these and halfchannels is that xchannels
* do have an *upstream* id, because upstream has already accepted
* the channel request from the server. This arises in the case of
* X forwarding, where we have to accept the request and read the
* X authorisation data before we know whether the channel needs
* to be forwarded to a downstream. */
tree234 *xchannels_by_us; /* stores 'struct share_xchannel' */
tree234 *xchannels_by_server; /* stores 'struct share_xchannel' */
/* Remote port forwarding requests in force. */
tree234 *forwardings; /* stores 'struct share_forwarding' */
/* Global requests we've sent on to the server, pending replies. */
struct share_globreq *globreq_head, *globreq_tail;
};
struct share_halfchannel {
unsigned server_id;
};
/* States of a share_channel. */
enum {
OPEN,
SENT_CLOSE,
RCVD_CLOSE,
/* Downstream has sent CHANNEL_OPEN but server hasn't replied yet.
* If downstream goes away when a channel is in this state, we
* must wait for the server's response before starting to send
* CLOSE. Channels in this state are also not held in
* channels_by_server, because their server_id field is
* meaningless. */
UNACKNOWLEDGED
};
struct share_channel {
unsigned downstream_id, upstream_id, server_id;
int downstream_maxpkt;
int state;
/*
* Some channels (specifically, channels on which downstream has
* sent "x11-req") have the additional function of storing a set
* of downstream X authorisation data and a handle to an upstream
* fake set.
*/
struct X11FakeAuth *x11_auth_upstream;
int x11_auth_proto;
char *x11_auth_data;
int x11_auth_datalen;
int x11_one_shot;
};
struct share_forwarding {
char *host;
int port;
int active; /* has the server sent REQUEST_SUCCESS? */
};
struct share_xchannel_message {
struct share_xchannel_message *next;
int type;
unsigned char *data;
int datalen;
};
struct share_xchannel {
unsigned upstream_id, server_id;
/*
* xchannels come in two flavours: live and dead. Live ones are
* waiting for an OPEN_CONFIRMATION or OPEN_FAILURE from
* downstream; dead ones have had an OPEN_FAILURE, so they only
* exist as a means of letting us conveniently respond to further
* channel messages from the server until such time as the server
* sends us CHANNEL_CLOSE.
*/
int live;
/*
* When we receive OPEN_CONFIRMATION, we will need to send a
* WINDOW_ADJUST to the server to synchronise the windows. For
* this purpose we need to know what window we have so far offered
* the server. We record this as exactly the value in the
* OPEN_CONFIRMATION that upstream sent us, adjusted by the amount
* by which the two X greetings differed in length.
*/
int window;
/*
* Linked list of SSH messages from the server relating to this
* channel, which we queue up until downstream sends us an
* OPEN_CONFIRMATION and we can belatedly send them all on.
*/
struct share_xchannel_message *msghead, *msgtail;
};
enum {
GLOBREQ_TCPIP_FORWARD,
GLOBREQ_CANCEL_TCPIP_FORWARD
};
struct share_globreq {
struct share_globreq *next;
int type;
int want_reply;
struct share_forwarding *fwd;
};
static int share_connstate_cmp(void *av, void *bv)
{
const struct ssh_sharing_connstate *a =
(const struct ssh_sharing_connstate *)av;
const struct ssh_sharing_connstate *b =
(const struct ssh_sharing_connstate *)bv;
if (a->id < b->id)
return -1;
else if (a->id > b->id)
return +1;
else
return 0;
}
static unsigned share_find_unused_id
(struct ssh_sharing_state *sharestate, unsigned first)
{
int low_orig, low, mid, high, high_orig;
struct ssh_sharing_connstate *cs;
unsigned ret;
/*
* Find the lowest unused downstream ID greater or equal to
* 'first'.
*
* Begin by seeing if 'first' itself is available. If it is, we'll
* just return it; if it's already in the tree, we'll find the
* tree index where it appears and use that for the next stage.
*/
{
struct ssh_sharing_connstate dummy;
dummy.id = first;
cs = findrelpos234(sharestate->connections, &dummy, NULL,
REL234_GE, &low_orig);
if (!cs)
return first;
}
/*
* Now binary-search using the counted B-tree, to find the largest
* ID which is in a contiguous sequence from the beginning of that
* range.
*/
low = low_orig;
high = high_orig = count234(sharestate->connections);
while (high - low > 1) {
mid = (high + low) / 2;
cs = index234(sharestate->connections, mid);
if (cs->id == first + (mid - low_orig))
low = mid; /* this one is still in the sequence */
else
high = mid; /* this one is past the end */
}
/*
* Now low is the tree index of the largest ID in the initial
* sequence. So the return value is one more than low's id, and we
* know low's id is given by the formula in the binary search loop
* above.
*
* (If an SSH connection went on for _enormously_ long, we might
* reach a point where all ids from 'first' to UINT_MAX were in
* use. In that situation the formula below would wrap round by
* one and return zero, which is conveniently the right way to
* signal 'no id available' from this function.)
*/
ret = first + (low - low_orig) + 1;
{
struct ssh_sharing_connstate dummy;
dummy.id = ret;
assert(NULL == find234(sharestate->connections, &dummy, NULL));
}
return ret;
}
static int share_halfchannel_cmp(void *av, void *bv)
{
const struct share_halfchannel *a = (const struct share_halfchannel *)av;
const struct share_halfchannel *b = (const struct share_halfchannel *)bv;
if (a->server_id < b->server_id)
return -1;
else if (a->server_id > b->server_id)
return +1;
else
return 0;
}
static int share_channel_us_cmp(void *av, void *bv)
{
const struct share_channel *a = (const struct share_channel *)av;
const struct share_channel *b = (const struct share_channel *)bv;
if (a->upstream_id < b->upstream_id)
return -1;
else if (a->upstream_id > b->upstream_id)
return +1;
else
return 0;
}
static int share_channel_server_cmp(void *av, void *bv)
{
const struct share_channel *a = (const struct share_channel *)av;
const struct share_channel *b = (const struct share_channel *)bv;
if (a->server_id < b->server_id)
return -1;
else if (a->server_id > b->server_id)
return +1;
else
return 0;
}
static int share_xchannel_us_cmp(void *av, void *bv)
{
const struct share_xchannel *a = (const struct share_xchannel *)av;
const struct share_xchannel *b = (const struct share_xchannel *)bv;
if (a->upstream_id < b->upstream_id)
return -1;
else if (a->upstream_id > b->upstream_id)
return +1;
else
return 0;
}
static int share_xchannel_server_cmp(void *av, void *bv)
{
const struct share_xchannel *a = (const struct share_xchannel *)av;
const struct share_xchannel *b = (const struct share_xchannel *)bv;
if (a->server_id < b->server_id)
return -1;
else if (a->server_id > b->server_id)
return +1;
else
return 0;
}
static int share_forwarding_cmp(void *av, void *bv)
{
const struct share_forwarding *a = (const struct share_forwarding *)av;
const struct share_forwarding *b = (const struct share_forwarding *)bv;
int i;
if ((i = strcmp(a->host, b->host)) != 0)
return i;
else if (a->port < b->port)
return -1;
else if (a->port > b->port)
return +1;
else
return 0;
}
static void share_xchannel_free(struct share_xchannel *xc)
{
while (xc->msghead) {
struct share_xchannel_message *tmp = xc->msghead;
xc->msghead = tmp->next;
sfree(tmp);
}
sfree(xc);
}
static void share_connstate_free(struct ssh_sharing_connstate *cs)
{
struct share_halfchannel *hc;
struct share_xchannel *xc;
struct share_channel *chan;
struct share_forwarding *fwd;
while ((hc = (struct share_halfchannel *)
delpos234(cs->halfchannels, 0)) != NULL)
sfree(hc);
freetree234(cs->halfchannels);
/* All channels live in 'channels_by_us' but only some in
* 'channels_by_server', so we use the former to find the list of
* ones to free */
freetree234(cs->channels_by_server);
while ((chan = (struct share_channel *)
delpos234(cs->channels_by_us, 0)) != NULL)
sfree(chan);
freetree234(cs->channels_by_us);
/* But every xchannel is in both trees, so it doesn't matter which
* we use to free them. */
while ((xc = (struct share_xchannel *)
delpos234(cs->xchannels_by_us, 0)) != NULL)
share_xchannel_free(xc);
freetree234(cs->xchannels_by_us);
freetree234(cs->xchannels_by_server);
while ((fwd = (struct share_forwarding *)
delpos234(cs->forwardings, 0)) != NULL)
sfree(fwd);
freetree234(cs->forwardings);
while (cs->globreq_head) {
struct share_globreq *globreq = cs->globreq_head;
cs->globreq_head = cs->globreq_head->next;
sfree(globreq);
}
sfree(cs);
}
void sharestate_free(void *v)
{
struct ssh_sharing_state *sharestate = (struct ssh_sharing_state *)v;
struct ssh_sharing_connstate *cs;
platform_ssh_share_cleanup(sharestate->sockname);
while ((cs = (struct ssh_sharing_connstate *)
delpos234(sharestate->connections, 0)) != NULL) {
share_connstate_free(cs);
}
freetree234(sharestate->connections);
if (sharestate->listensock) {
sk_close(sharestate->listensock);
sharestate->listensock = NULL;
}
sfree(sharestate->server_verstring);
sfree(sharestate->sockname);
sfree(sharestate);
}
static struct share_halfchannel *share_add_halfchannel
(struct ssh_sharing_connstate *cs, unsigned server_id)
{
struct share_halfchannel *hc = snew(struct share_halfchannel);
hc->server_id = server_id;
if (add234(cs->halfchannels, hc) != hc) {
/* Duplicate?! */
sfree(hc);
return NULL;
} else {
return hc;
}
}
static struct share_halfchannel *share_find_halfchannel
(struct ssh_sharing_connstate *cs, unsigned server_id)
{
struct share_halfchannel dummyhc;
dummyhc.server_id = server_id;
return find234(cs->halfchannels, &dummyhc, NULL);
}
static void share_remove_halfchannel(struct ssh_sharing_connstate *cs,
struct share_halfchannel *hc)
{
del234(cs->halfchannels, hc);
sfree(hc);
}
static struct share_channel *share_add_channel
(struct ssh_sharing_connstate *cs, unsigned downstream_id,
unsigned upstream_id, unsigned server_id, int state, int maxpkt)
{
struct share_channel *chan = snew(struct share_channel);
chan->downstream_id = downstream_id;
chan->upstream_id = upstream_id;
chan->server_id = server_id;
chan->state = state;
chan->downstream_maxpkt = maxpkt;
chan->x11_auth_upstream = NULL;
chan->x11_auth_data = NULL;
chan->x11_auth_proto = -1;
chan->x11_auth_datalen = 0;
chan->x11_one_shot = 0;
if (add234(cs->channels_by_us, chan) != chan) {
sfree(chan);
return NULL;
}
if (chan->state != UNACKNOWLEDGED) {
if (add234(cs->channels_by_server, chan) != chan) {
del234(cs->channels_by_us, chan);
sfree(chan);
return NULL;
}
}
return chan;
}
static void share_channel_set_server_id(struct ssh_sharing_connstate *cs,
struct share_channel *chan,
unsigned server_id, int newstate)
{
chan->server_id = server_id;
chan->state = newstate;
assert(newstate != UNACKNOWLEDGED);
add234(cs->channels_by_server, chan);
}
static struct share_channel *share_find_channel_by_upstream
(struct ssh_sharing_connstate *cs, unsigned upstream_id)
{
struct share_channel dummychan;
dummychan.upstream_id = upstream_id;
return find234(cs->channels_by_us, &dummychan, NULL);
}
static struct share_channel *share_find_channel_by_server
(struct ssh_sharing_connstate *cs, unsigned server_id)
{
struct share_channel dummychan;
dummychan.server_id = server_id;
return find234(cs->channels_by_server, &dummychan, NULL);
}
static void share_remove_channel(struct ssh_sharing_connstate *cs,
struct share_channel *chan)
{
del234(cs->channels_by_us, chan);
del234(cs->channels_by_server, chan);
if (chan->x11_auth_upstream)
ssh_sharing_remove_x11_display(cs->parent->ssh,
chan->x11_auth_upstream);
sfree(chan->x11_auth_data);
sfree(chan);
}
static struct share_xchannel *share_add_xchannel
(struct ssh_sharing_connstate *cs,
unsigned upstream_id, unsigned server_id)
{
struct share_xchannel *xc = snew(struct share_xchannel);
xc->upstream_id = upstream_id;
xc->server_id = server_id;
xc->live = TRUE;
xc->msghead = xc->msgtail = NULL;
if (add234(cs->xchannels_by_us, xc) != xc) {
sfree(xc);
return NULL;
}
if (add234(cs->xchannels_by_server, xc) != xc) {
del234(cs->xchannels_by_us, xc);
sfree(xc);
return NULL;
}
return xc;
}
static struct share_xchannel *share_find_xchannel_by_upstream
(struct ssh_sharing_connstate *cs, unsigned upstream_id)
{
struct share_xchannel dummyxc;
dummyxc.upstream_id = upstream_id;
return find234(cs->xchannels_by_us, &dummyxc, NULL);
}
static struct share_xchannel *share_find_xchannel_by_server
(struct ssh_sharing_connstate *cs, unsigned server_id)
{
struct share_xchannel dummyxc;
dummyxc.server_id = server_id;
return find234(cs->xchannels_by_server, &dummyxc, NULL);
}
static void share_remove_xchannel(struct ssh_sharing_connstate *cs,
struct share_xchannel *xc)
{
del234(cs->xchannels_by_us, xc);
del234(cs->xchannels_by_server, xc);
share_xchannel_free(xc);
}
static struct share_forwarding *share_add_forwarding
(struct ssh_sharing_connstate *cs,
const char *host, int port)
{
struct share_forwarding *fwd = snew(struct share_forwarding);
fwd->host = dupstr(host);
fwd->port = port;
fwd->active = FALSE;
if (add234(cs->forwardings, fwd) != fwd) {
/* Duplicate?! */
sfree(fwd);
return NULL;
}
return fwd;
}
static struct share_forwarding *share_find_forwarding
(struct ssh_sharing_connstate *cs, const char *host, int port)
{
struct share_forwarding dummyfwd, *ret;
dummyfwd.host = dupstr(host);
dummyfwd.port = port;
ret = find234(cs->forwardings, &dummyfwd, NULL);
sfree(dummyfwd.host);
return ret;
}
static void share_remove_forwarding(struct ssh_sharing_connstate *cs,
struct share_forwarding *fwd)
{
del234(cs->forwardings, fwd);
sfree(fwd);
}
static void send_packet_to_downstream(struct ssh_sharing_connstate *cs,
int type, const void *pkt, int pktlen,
struct share_channel *chan)
{
if (!cs->sock) /* throw away all packets destined for a dead downstream */
return;
if (type == SSH2_MSG_CHANNEL_DATA) {
/*
* Special case which we take care of at a low level, so as to
* be sure to apply it in all cases. On rare occasions we
* might find that we have a channel for which the
* downstream's maximum packet size exceeds the max packet
* size we presented to the server on its behalf. (This can
* occur in X11 forwarding, where we have to send _our_
* CHANNEL_OPEN_CONFIRMATION before we discover which if any
* downstream the channel is destined for, so if that
* downstream turns out to present a smaller max packet size
* then we're in this situation.)
*
* If that happens, we just chop up the packet into pieces and
* send them as separate CHANNEL_DATA packets.
*/
const char *upkt = (const char *)pkt;
char header[13]; /* 4 length + 1 type + 4 channel id + 4 string len */
int len = toint(GET_32BIT(upkt + 4));
upkt += 8; /* skip channel id + length field */
if (len < 0 || len > pktlen - 8)
len = pktlen - 8;
do {
int this_len = (len > chan->downstream_maxpkt ?
chan->downstream_maxpkt : len);
PUT_32BIT(header, this_len + 9);
header[4] = type;
PUT_32BIT(header + 5, chan->downstream_id);
PUT_32BIT(header + 9, this_len);
sk_write(cs->sock, header, 13);
sk_write(cs->sock, upkt, this_len);
len -= this_len;
upkt += this_len;
} while (len > 0);
} else {
/*
* Just do the obvious thing.
*/
char header[9];
PUT_32BIT(header, pktlen + 1);
header[4] = type;
sk_write(cs->sock, header, 5);
sk_write(cs->sock, pkt, pktlen);
}
}
static void share_try_cleanup(struct ssh_sharing_connstate *cs)
{
int i;
struct share_halfchannel *hc;
struct share_channel *chan;
struct share_forwarding *fwd;
/*
* Any half-open channels, i.e. those for which we'd received
* CHANNEL_OPEN from the server but not passed back a response
* from downstream, should be responded to with OPEN_FAILURE.
*/
while ((hc = (struct share_halfchannel *)
index234(cs->halfchannels, 0)) != NULL) {
static const char reason[] = "PuTTY downstream no longer available";
static const char lang[] = "en";
unsigned char packet[256];
int pos = 0;
PUT_32BIT(packet + pos, hc->server_id); pos += 4;
PUT_32BIT(packet + pos, SSH2_OPEN_CONNECT_FAILED); pos += 4;
PUT_32BIT(packet + pos, strlen(reason)); pos += 4;
memcpy(packet + pos, reason, strlen(reason)); pos += strlen(reason);
PUT_32BIT(packet + pos, strlen(lang)); pos += 4;
memcpy(packet + pos, lang, strlen(lang)); pos += strlen(lang);
ssh_send_packet_from_downstream(cs->parent->ssh, cs->id,
SSH2_MSG_CHANNEL_OPEN_FAILURE,
packet, pos, "cleanup after"
" downstream went away");
share_remove_halfchannel(cs, hc);
}
/*
* Any actually open channels should have a CHANNEL_CLOSE sent for
* them, unless we've already done so. We won't be able to
* actually clean them up until CHANNEL_CLOSE comes back from the
* server, though (unless the server happens to have sent a CLOSE
* already).
*
* Another annoying exception is UNACKNOWLEDGED channels, i.e.
* we've _sent_ a CHANNEL_OPEN to the server but not received an
* OPEN_CONFIRMATION or OPEN_FAILURE. We must wait for a reply
* before closing the channel, because until we see that reply we
* won't have the server's channel id to put in the close message.
*/
for (i = 0; (chan = (struct share_channel *)
index234(cs->channels_by_us, i)) != NULL; i++) {
unsigned char packet[256];
int pos = 0;
if (chan->state != SENT_CLOSE && chan->state != UNACKNOWLEDGED) {
PUT_32BIT(packet + pos, chan->server_id); pos += 4;
ssh_send_packet_from_downstream(cs->parent->ssh, cs->id,
SSH2_MSG_CHANNEL_CLOSE,
packet, pos, "cleanup after"
" downstream went away");
if (chan->state != RCVD_CLOSE) {
chan->state = SENT_CLOSE;
} else {
/* In this case, we _can_ clear up the channel now. */
ssh_delete_sharing_channel(cs->parent->ssh, chan->upstream_id);
share_remove_channel(cs, chan);
i--; /* don't accidentally skip one as a result */
}
}
}
/*
* Any remote port forwardings we're managing on behalf of this
* downstream should be cancelled. Again, we must defer those for
* which we haven't yet seen REQUEST_SUCCESS/FAILURE.
*
* We take a fire-and-forget approach during cleanup, not
* bothering to set want_reply.
*/
for (i = 0; (fwd = (struct share_forwarding *)
index234(cs->forwardings, i)) != NULL; i++) {
if (fwd->active) {
static const char request[] = "cancel-tcpip-forward";
char *packet = snewn(256 + strlen(fwd->host), char);
int pos = 0;
PUT_32BIT(packet + pos, strlen(request)); pos += 4;
memcpy(packet + pos, request, strlen(request));
pos += strlen(request);
packet[pos++] = 0; /* !want_reply */
PUT_32BIT(packet + pos, strlen(fwd->host)); pos += 4;
memcpy(packet + pos, fwd->host, strlen(fwd->host));
pos += strlen(fwd->host);
PUT_32BIT(packet + pos, fwd->port); pos += 4;
ssh_send_packet_from_downstream(cs->parent->ssh, cs->id,
SSH2_MSG_GLOBAL_REQUEST,
packet, pos, "cleanup after"
" downstream went away");
sfree(packet);
share_remove_forwarding(cs, fwd);
i--; /* don't accidentally skip one as a result */
}
}
if (count234(cs->halfchannels) == 0 &&
count234(cs->channels_by_us) == 0 &&
count234(cs->forwardings) == 0) {
/*
* Now we're _really_ done, so we can get rid of cs completely.
*/
del234(cs->parent->connections, cs);
ssh_sharing_downstream_disconnected(cs->parent->ssh, cs->id);
share_connstate_free(cs);
}
}
static void share_begin_cleanup(struct ssh_sharing_connstate *cs)
{
sk_close(cs->sock);
cs->sock = NULL;
share_try_cleanup(cs);
}
static void share_disconnect(struct ssh_sharing_connstate *cs,
const char *message)
{
static const char lang[] = "en";
int msglen = strlen(message);
char *packet = snewn(msglen + 256, char);
int pos = 0;
PUT_32BIT(packet + pos, SSH2_DISCONNECT_PROTOCOL_ERROR); pos += 4;
PUT_32BIT(packet + pos, msglen); pos += 4;
memcpy(packet + pos, message, msglen);
pos += msglen;
PUT_32BIT(packet + pos, strlen(lang)); pos += 4;
memcpy(packet + pos, lang, strlen(lang)); pos += strlen(lang);
send_packet_to_downstream(cs, SSH2_MSG_DISCONNECT, packet, pos, NULL);
share_begin_cleanup(cs);
}
static int share_closing(Plug plug, const char *error_msg, int error_code,
int calling_back)
{
struct ssh_sharing_connstate *cs = (struct ssh_sharing_connstate *)plug;
if (error_msg)
ssh_sharing_logf(cs->parent->ssh, cs->id, "%s", error_msg);
share_begin_cleanup(cs);
return 1;
}
static int getstring_inner(const void *vdata, int datalen,
char **out, int *outlen)
{
const unsigned char *data = (const unsigned char *)vdata;
int len;
if (datalen < 4)
return FALSE;
len = toint(GET_32BIT(data));
if (len < 0 || len > datalen - 4)
return FALSE;
if (outlen)
*outlen = len + 4; /* total size including length field */
if (out)
*out = dupprintf("%.*s", len, (char *)data + 4);
return TRUE;
}
static char *getstring(const void *data, int datalen)
{
char *ret;
if (getstring_inner(data, datalen, &ret, NULL))
return ret;
else
return NULL;
}
static int getstring_size(const void *data, int datalen)
{
int ret;
if (getstring_inner(data, datalen, NULL, &ret))
return ret;
else
return -1;
}
/*
* Append a message to the end of an xchannel's queue, with the length
* and type code filled in and the data block allocated but
* uninitialised.
*/
struct share_xchannel_message *share_xchannel_add_message
(struct share_xchannel *xc, int type, int len)
{
unsigned char *block;
struct share_xchannel_message *msg;
/*
* Be a little tricksy here by allocating a single memory block
* containing both the 'struct share_xchannel_message' and the
* actual data. Simplifies freeing it later.
*/
block = smalloc(sizeof(struct share_xchannel_message) + len);
msg = (struct share_xchannel_message *)block;
msg->data = block + sizeof(struct share_xchannel_message);
msg->datalen = len;
msg->type = type;
/*
* Queue it in the xchannel.
*/
if (xc->msgtail)
xc->msgtail->next = msg;
else
xc->msghead = msg;
msg->next = NULL;
xc->msgtail = msg;
return msg;
}
void share_dead_xchannel_respond(struct ssh_sharing_connstate *cs,
struct share_xchannel *xc)
{
/*
* Handle queued incoming messages from the server destined for an
* xchannel which is dead (i.e. downstream sent OPEN_FAILURE).
*/
int delete = FALSE;
while (xc->msghead) {
struct share_xchannel_message *msg = xc->msghead;
xc->msghead = msg->next;
if (msg->type == SSH2_MSG_CHANNEL_REQUEST && msg->datalen > 4) {
/*
* A CHANNEL_REQUEST is responded to by sending
* CHANNEL_FAILURE, if it has want_reply set.
*/
int wantreplypos = getstring_size(msg->data, msg->datalen);
if (wantreplypos > 0 && wantreplypos < msg->datalen &&
msg->data[wantreplypos] != 0) {
unsigned char id[4];
PUT_32BIT(id, xc->server_id);
ssh_send_packet_from_downstream
(cs->parent->ssh, cs->id, SSH2_MSG_CHANNEL_FAILURE, id, 4,
"downstream refused X channel open");
}
} else if (msg->type == SSH2_MSG_CHANNEL_CLOSE) {
/*
* On CHANNEL_CLOSE we can discard the channel completely.
*/
delete = TRUE;
}
sfree(msg);
}
xc->msgtail = NULL;
if (delete) {
ssh_delete_sharing_channel(cs->parent->ssh, xc->upstream_id);
share_remove_xchannel(cs, xc);
}
}
void share_xchannel_confirmation(struct ssh_sharing_connstate *cs,
struct share_xchannel *xc,
struct share_channel *chan,
unsigned downstream_window)
{
unsigned char window_adjust[8];
/*
* Send all the queued messages downstream.
*/
while (xc->msghead) {
struct share_xchannel_message *msg = xc->msghead;
xc->msghead = msg->next;
if (msg->datalen >= 4)
PUT_32BIT(msg->data, chan->downstream_id);
send_packet_to_downstream(cs, msg->type,
msg->data, msg->datalen, chan);
sfree(msg);
}
/*
* Send a WINDOW_ADJUST back upstream, to synchronise the window
* size downstream thinks it's presented with the one we've
* actually presented.
*/
PUT_32BIT(window_adjust, xc->server_id);
PUT_32BIT(window_adjust + 4, downstream_window - xc->window);
ssh_send_packet_from_downstream(cs->parent->ssh, cs->id,
SSH2_MSG_CHANNEL_WINDOW_ADJUST,
window_adjust, 8, "window adjustment after"
" downstream accepted X channel");
}
void share_xchannel_failure(struct ssh_sharing_connstate *cs,
struct share_xchannel *xc)
{
/*
* If downstream refuses to open our X channel at all for some
* reason, we must respond by sending an emergency CLOSE upstream.
*/
unsigned char id[4];
PUT_32BIT(id, xc->server_id);
ssh_send_packet_from_downstream
(cs->parent->ssh, cs->id, SSH2_MSG_CHANNEL_CLOSE, id, 4,
"downstream refused X channel open");
/*
* Now mark the xchannel as dead, and respond to anything sent on
* it until we see CLOSE for it in turn.
*/
xc->live = FALSE;
share_dead_xchannel_respond(cs, xc);
}
void share_setup_x11_channel(void *csv, void *chanv,
unsigned upstream_id, unsigned server_id,
unsigned server_currwin, unsigned server_maxpkt,
unsigned client_adjusted_window,
const char *peer_addr, int peer_port, int endian,
int protomajor, int protominor,
const void *initial_data, int initial_len)
{
struct ssh_sharing_connstate *cs = (struct ssh_sharing_connstate *)csv;
struct share_channel *chan = (struct share_channel *)chanv;
struct share_xchannel *xc;
struct share_xchannel_message *msg;
void *greeting;
int greeting_len;
unsigned char *pkt;
int pktlen;
/*
* Create an xchannel containing data we've already received from
* the X client, and preload it with a CHANNEL_DATA message
* containing our own made-up authorisation greeting and any
* additional data sent from the server so far.
*/
xc = share_add_xchannel(cs, upstream_id, server_id);
greeting = x11_make_greeting(endian, protomajor, protominor,
chan->x11_auth_proto,
chan->x11_auth_data, chan->x11_auth_datalen,
peer_addr, peer_port, &greeting_len);
msg = share_xchannel_add_message(xc, SSH2_MSG_CHANNEL_DATA,
8 + greeting_len + initial_len);
/* leave the channel id field unfilled - we don't know the
* downstream id yet, of course */
PUT_32BIT(msg->data + 4, greeting_len + initial_len);
memcpy(msg->data + 8, greeting, greeting_len);
memcpy(msg->data + 8 + greeting_len, initial_data, initial_len);
sfree(greeting);
xc->window = client_adjusted_window + greeting_len;
/*
* Send on a CHANNEL_OPEN to downstream.
*/
pktlen = 27 + strlen(peer_addr);
pkt = snewn(pktlen, unsigned char);
PUT_32BIT(pkt, 3); /* strlen("x11") */
memcpy(pkt+4, "x11", 3);
PUT_32BIT(pkt+7, server_id);
PUT_32BIT(pkt+11, server_currwin);
PUT_32BIT(pkt+15, server_maxpkt);
PUT_32BIT(pkt+19, strlen(peer_addr));
memcpy(pkt+23, peer_addr, strlen(peer_addr));
PUT_32BIT(pkt+23+strlen(peer_addr), peer_port);
send_packet_to_downstream(cs, SSH2_MSG_CHANNEL_OPEN, pkt, pktlen, NULL);
sfree(pkt);
/*
* If this was a once-only X forwarding, clean it up now.
*/
if (chan->x11_one_shot) {
ssh_sharing_remove_x11_display(cs->parent->ssh,
chan->x11_auth_upstream);
chan->x11_auth_upstream = NULL;
sfree(chan->x11_auth_data);
chan->x11_auth_proto = -1;
chan->x11_auth_datalen = 0;
chan->x11_one_shot = 0;
}
}
void share_got_pkt_from_server(void *csv, int type,
unsigned char *pkt, int pktlen)
{
struct ssh_sharing_connstate *cs = (struct ssh_sharing_connstate *)csv;
struct share_globreq *globreq;
int id_pos;
unsigned upstream_id, server_id;
struct share_channel *chan;
struct share_xchannel *xc;
switch (type) {
case SSH2_MSG_REQUEST_SUCCESS:
case SSH2_MSG_REQUEST_FAILURE:
globreq = cs->globreq_head;
if (globreq->type == GLOBREQ_TCPIP_FORWARD) {
if (type == SSH2_MSG_REQUEST_FAILURE) {
share_remove_forwarding(cs, globreq->fwd);
} else {
globreq->fwd->active = TRUE;
}
} else if (globreq->type == GLOBREQ_CANCEL_TCPIP_FORWARD) {
if (type == SSH2_MSG_REQUEST_SUCCESS) {
share_remove_forwarding(cs, globreq->fwd);
}
}
if (globreq->want_reply) {
send_packet_to_downstream(cs, type, pkt, pktlen, NULL);
}
cs->globreq_head = globreq->next;
sfree(globreq);
if (cs->globreq_head == NULL)
cs->globreq_tail = NULL;
if (!cs->sock) {
/* Retry cleaning up this connection, in case that reply
* was the last thing we were waiting for. */
share_try_cleanup(cs);
}
break;
case SSH2_MSG_CHANNEL_OPEN:
id_pos = getstring_size(pkt, pktlen);
assert(id_pos >= 0);
server_id = GET_32BIT(pkt + id_pos);
share_add_halfchannel(cs, server_id);
send_packet_to_downstream(cs, type, pkt, pktlen, NULL);
break;
case SSH2_MSG_CHANNEL_OPEN_CONFIRMATION:
case SSH2_MSG_CHANNEL_OPEN_FAILURE:
case SSH2_MSG_CHANNEL_CLOSE:
case SSH2_MSG_CHANNEL_WINDOW_ADJUST:
case SSH2_MSG_CHANNEL_DATA:
case SSH2_MSG_CHANNEL_EXTENDED_DATA:
case SSH2_MSG_CHANNEL_EOF:
case SSH2_MSG_CHANNEL_REQUEST:
case SSH2_MSG_CHANNEL_SUCCESS:
case SSH2_MSG_CHANNEL_FAILURE:
/*
* All these messages have the recipient channel id as the
* first uint32 field in the packet. Substitute the downstream
* channel id for our one and pass the packet downstream.
*/
assert(pktlen >= 4);
upstream_id = GET_32BIT(pkt);
if ((chan = share_find_channel_by_upstream(cs, upstream_id)) != NULL) {
/*
* The normal case: this id refers to an open channel.
*/
PUT_32BIT(pkt, chan->downstream_id);
send_packet_to_downstream(cs, type, pkt, pktlen, chan);
/*
* Update the channel state, for messages that need it.
*/
if (type == SSH2_MSG_CHANNEL_OPEN_CONFIRMATION) {
if (chan->state == UNACKNOWLEDGED && pktlen >= 8) {
share_channel_set_server_id(cs, chan, GET_32BIT(pkt+4),
OPEN);
if (!cs->sock) {
/* Retry cleaning up this connection, so that we
* can send an immediate CLOSE on this channel for
* which we now know the server id. */
share_try_cleanup(cs);
}
}
} else if (type == SSH2_MSG_CHANNEL_OPEN_FAILURE) {
ssh_delete_sharing_channel(cs->parent->ssh, chan->upstream_id);
share_remove_channel(cs, chan);
} else if (type == SSH2_MSG_CHANNEL_CLOSE) {
if (chan->state == SENT_CLOSE) {
ssh_delete_sharing_channel(cs->parent->ssh,
chan->upstream_id);
share_remove_channel(cs, chan);
if (!cs->sock) {
/* Retry cleaning up this connection, in case this
* channel closure was the last thing we were
* waiting for. */
share_try_cleanup(cs);
}
} else {
chan->state = RCVD_CLOSE;
}
}
} else if ((xc = share_find_xchannel_by_upstream(cs, upstream_id))
!= NULL) {
/*
* The unusual case: this id refers to an xchannel. Add it
* to the xchannel's queue.
*/
struct share_xchannel_message *msg;
msg = share_xchannel_add_message(xc, type, pktlen);
memcpy(msg->data, pkt, pktlen);
/* If the xchannel is dead, then also respond to it (which
* may involve deleting the channel). */
if (!xc->live)
share_dead_xchannel_respond(cs, xc);
}
break;
default:
assert(!"This packet type should never have come from ssh.c");
break;
}
}
static void share_got_pkt_from_downstream(struct ssh_sharing_connstate *cs,
int type,
unsigned char *pkt, int pktlen)
{
char *request_name;
struct share_forwarding *fwd;
int id_pos;
unsigned old_id, new_id, server_id;
struct share_globreq *globreq;
struct share_channel *chan;
struct share_halfchannel *hc;
struct share_xchannel *xc;
char *err = NULL;
switch (type) {
case SSH2_MSG_DISCONNECT:
/*
* This message stops here: if downstream is disconnecting
* from us, that doesn't mean we want to disconnect from the
* SSH server. Close the downstream connection and start
* cleanup.
*/
share_begin_cleanup(cs);
break;
case SSH2_MSG_GLOBAL_REQUEST:
/*
* The only global requests we understand are "tcpip-forward"
* and "cancel-tcpip-forward". Since those require us to
* maintain state, we must assume that other global requests
* will probably require that too, and so we don't forward on
* any request we don't understand.
*/
request_name = getstring(pkt, pktlen);
if (request_name == NULL) {
err = dupprintf("Truncated GLOBAL_REQUEST packet");
goto confused;
}
if (!strcmp(request_name, "tcpip-forward")) {
int wantreplypos, orig_wantreply, port, ret;
char *host;
sfree(request_name);
/*
* Pick the packet apart to find the want_reply field and
* the host/port we're going to ask to listen on.
*/
wantreplypos = getstring_size(pkt, pktlen);
if (wantreplypos < 0 || wantreplypos >= pktlen) {
err = dupprintf("Truncated GLOBAL_REQUEST packet");
goto confused;
}
orig_wantreply = pkt[wantreplypos];
port = getstring_size(pkt + (wantreplypos + 1),
pktlen - (wantreplypos + 1));
port += (wantreplypos + 1);
if (port < 0 || port > pktlen - 4) {
err = dupprintf("Truncated GLOBAL_REQUEST packet");
goto confused;
}
host = getstring(pkt + (wantreplypos + 1),
pktlen - (wantreplypos + 1));
assert(host != NULL);
port = GET_32BIT(pkt + port);
/*
* See if we can allocate space in ssh.c's tree of remote
* port forwardings. If we can't, it's because another
* client sharing this connection has already allocated
* the identical port forwarding, so we take it on
* ourselves to manufacture a failure packet and send it
* back to downstream.
*/
ret = ssh_alloc_sharing_rportfwd(cs->parent->ssh, host, port, cs);
if (!ret) {
if (orig_wantreply) {
send_packet_to_downstream(cs, SSH2_MSG_REQUEST_FAILURE,
"", 0, NULL);
}
} else {
/*
* We've managed to make space for this forwarding
* locally. Pass the request on to the SSH server, but
* set want_reply even if it wasn't originally set, so
* that we know whether this forwarding needs to be
* cleaned up if downstream goes away.
*/
int old_wantreply = pkt[wantreplypos];
pkt[wantreplypos] = 1;
ssh_send_packet_from_downstream
(cs->parent->ssh, cs->id, type, pkt, pktlen,
old_wantreply ? NULL : "upstream added want_reply flag");
fwd = share_add_forwarding(cs, host, port);
ssh_sharing_queue_global_request(cs->parent->ssh, cs);
if (fwd) {
globreq = snew(struct share_globreq);
globreq->next = NULL;
if (cs->globreq_tail)
cs->globreq_tail->next = globreq;
else
cs->globreq_head = globreq;
globreq->fwd = fwd;
globreq->want_reply = orig_wantreply;
globreq->type = GLOBREQ_TCPIP_FORWARD;
}
}
sfree(host);
} else if (!strcmp(request_name, "cancel-tcpip-forward")) {
int wantreplypos, orig_wantreply, port;
char *host;
struct share_forwarding *fwd;
sfree(request_name);
/*
* Pick the packet apart to find the want_reply field and
* the host/port we're going to ask to listen on.
*/
wantreplypos = getstring_size(pkt, pktlen);
if (wantreplypos < 0 || wantreplypos >= pktlen) {
err = dupprintf("Truncated GLOBAL_REQUEST packet");
goto confused;
}
orig_wantreply = pkt[wantreplypos];
port = getstring_size(pkt + (wantreplypos + 1),
pktlen - (wantreplypos + 1));
port += (wantreplypos + 1);
if (port < 0 || port > pktlen - 4) {
err = dupprintf("Truncated GLOBAL_REQUEST packet");
goto confused;
}
host = getstring(pkt + (wantreplypos + 1),
pktlen - (wantreplypos + 1));
assert(host != NULL);
port = GET_32BIT(pkt + port);
/*
* Look up the existing forwarding with these details.
*/
fwd = share_find_forwarding(cs, host, port);
if (!fwd) {
if (orig_wantreply) {
send_packet_to_downstream(cs, SSH2_MSG_REQUEST_FAILURE,
"", 0, NULL);
}
} else {
/*
* Pass the cancel request on to the SSH server, but
* set want_reply even if it wasn't originally set, so
* that _we_ know whether the forwarding has been
* deleted even if downstream doesn't want to know.
*/
int old_wantreply = pkt[wantreplypos];
pkt[wantreplypos] = 1;
ssh_send_packet_from_downstream
(cs->parent->ssh, cs->id, type, pkt, pktlen,
old_wantreply ? NULL : "upstream added want_reply flag");
ssh_sharing_queue_global_request(cs->parent->ssh, cs);
}
sfree(host);
} else {
/*
* Request we don't understand. Manufacture a failure
* message if an answer was required.
*/
int wantreplypos;
sfree(request_name);
wantreplypos = getstring_size(pkt, pktlen);
if (wantreplypos < 0 || wantreplypos >= pktlen) {
err = dupprintf("Truncated GLOBAL_REQUEST packet");
goto confused;
}
if (pkt[wantreplypos])
send_packet_to_downstream(cs, SSH2_MSG_REQUEST_FAILURE,
"", 0, NULL);
}
break;
case SSH2_MSG_CHANNEL_OPEN:
/* Sender channel id comes after the channel type string */
id_pos = getstring_size(pkt, pktlen);
if (id_pos < 0 || id_pos > pktlen - 12) {
err = dupprintf("Truncated CHANNEL_OPEN packet");
goto confused;
}
old_id = GET_32BIT(pkt + id_pos);
new_id = ssh_alloc_sharing_channel(cs->parent->ssh, cs);
share_add_channel(cs, old_id, new_id, 0, UNACKNOWLEDGED,
GET_32BIT(pkt + id_pos + 8));
PUT_32BIT(pkt + id_pos, new_id);
ssh_send_packet_from_downstream(cs->parent->ssh, cs->id,
type, pkt, pktlen, NULL);
break;
case SSH2_MSG_CHANNEL_OPEN_CONFIRMATION:
if (pktlen < 16) {
err = dupprintf("Truncated CHANNEL_OPEN_CONFIRMATION packet");
goto confused;
}
id_pos = 4; /* sender channel id is 2nd uint32 field in packet */
old_id = GET_32BIT(pkt + id_pos);
server_id = GET_32BIT(pkt);
/* This server id may refer to either a halfchannel or an xchannel. */
hc = NULL, xc = NULL; /* placate optimiser */
if ((hc = share_find_halfchannel(cs, server_id)) != NULL) {
new_id = ssh_alloc_sharing_channel(cs->parent->ssh, cs);
} else if ((xc = share_find_xchannel_by_server(cs, server_id))
!= NULL) {
new_id = xc->upstream_id;
} else {
err = dupprintf("CHANNEL_OPEN_CONFIRMATION packet cited unknown channel %u", (unsigned)server_id);
goto confused;
}
PUT_32BIT(pkt + id_pos, new_id);
chan = share_add_channel(cs, old_id, new_id, server_id, OPEN,
GET_32BIT(pkt + 12));
if (hc) {
ssh_send_packet_from_downstream(cs->parent->ssh, cs->id,
type, pkt, pktlen, NULL);
share_remove_halfchannel(cs, hc);
} else if (xc) {
unsigned downstream_window = GET_32BIT(pkt + 8);
if (downstream_window < 256) {
err = dupprintf("Initial window size for x11 channel must be at least 256 (got %u)", downstream_window);
goto confused;
}
share_xchannel_confirmation(cs, xc, chan, downstream_window);
share_remove_xchannel(cs, xc);
}
break;
case SSH2_MSG_CHANNEL_OPEN_FAILURE:
if (pktlen < 4) {
err = dupprintf("Truncated CHANNEL_OPEN_FAILURE packet");
goto confused;
}
server_id = GET_32BIT(pkt);
/* This server id may refer to either a halfchannel or an xchannel. */
if ((hc = share_find_halfchannel(cs, server_id)) != NULL) {
ssh_send_packet_from_downstream(cs->parent->ssh, cs->id,
type, pkt, pktlen, NULL);
share_remove_halfchannel(cs, hc);
} else if ((xc = share_find_xchannel_by_server(cs, server_id))
!= NULL) {
share_xchannel_failure(cs, xc);
} else {
err = dupprintf("CHANNEL_OPEN_FAILURE packet cited unknown channel %u", (unsigned)server_id);
goto confused;
}
break;
case SSH2_MSG_CHANNEL_WINDOW_ADJUST:
case SSH2_MSG_CHANNEL_DATA:
case SSH2_MSG_CHANNEL_EXTENDED_DATA:
case SSH2_MSG_CHANNEL_EOF:
case SSH2_MSG_CHANNEL_CLOSE:
case SSH2_MSG_CHANNEL_REQUEST:
case SSH2_MSG_CHANNEL_SUCCESS:
case SSH2_MSG_CHANNEL_FAILURE:
case SSH2_MSG_IGNORE:
case SSH2_MSG_DEBUG:
if (type == SSH2_MSG_CHANNEL_REQUEST &&
(request_name = getstring(pkt + 4, pktlen - 4)) != NULL) {
/*
* Agent forwarding requests from downstream are treated
* specially. Because OpenSSHD doesn't let us enable agent
* forwarding independently per session channel, and in
* particular because the OpenSSH-defined agent forwarding
* protocol does not mark agent-channel requests with the
* id of the session channel they originate from, the only
* way we can implement agent forwarding in a
* connection-shared PuTTY is to forward the _upstream_
* agent. Hence, we unilaterally deny agent forwarding
* requests from downstreams if we aren't prepared to
* forward an agent ourselves.
*
* (If we are, then we dutifully pass agent forwarding
* requests upstream. OpenSSHD has the curious behaviour
* that all but the first such request will be rejected,
* but all session channels opened after the first request
* get agent forwarding enabled whether they ask for it or
* not; but that's not our concern, since other SSH
* servers supporting the same piece of protocol might in
* principle at least manage to enable agent forwarding on
* precisely the channels that requested it, even if the
* subsequent CHANNEL_OPENs still can't be associated with
* a parent session channel.)
*/
if (!strcmp(request_name, "auth-agent-req@openssh.com") &&
!ssh_agent_forwarding_permitted(cs->parent->ssh)) {
unsigned server_id = GET_32BIT(pkt);
unsigned char recipient_id[4];
sfree(request_name);
chan = share_find_channel_by_server(cs, server_id);
if (chan) {
PUT_32BIT(recipient_id, chan->downstream_id);
send_packet_to_downstream(cs, SSH2_MSG_CHANNEL_FAILURE,
recipient_id, 4, NULL);
} else {
char *buf = dupprintf("Agent forwarding request for "
"unrecognised channel %u", server_id);
share_disconnect(cs, buf);
sfree(buf);
return;
}
break;
}
/*
* Another thing we treat specially is X11 forwarding
* requests. For these, we have to make up another set of
* X11 auth data, and enter it into our SSH connection's
* list of possible X11 authorisation credentials so that
* when we see an X11 channel open request we can know
* whether it's one to handle locally or one to pass on to
* a downstream, and if the latter, which one.
*/
if (!strcmp(request_name, "x11-req")) {
unsigned server_id = GET_32BIT(pkt);
int want_reply, single_connection, screen;
char *auth_proto_str, *auth_data;
int auth_proto, protolen, datalen;
int pos;
sfree(request_name);
chan = share_find_channel_by_server(cs, server_id);
if (!chan) {
char *buf = dupprintf("X11 forwarding request for "
"unrecognised channel %u", server_id);
share_disconnect(cs, buf);
sfree(buf);
return;
}
/*
* Pick apart the whole message to find the downstream
* auth details.
*/
/* we have already seen: 4 bytes channel id, 4+7 request name */
if (pktlen < 17) {
err = dupprintf("Truncated CHANNEL_REQUEST(\"x11\") packet");
goto confused;
}
want_reply = pkt[15] != 0;
single_connection = pkt[16] != 0;
auth_proto_str = getstring(pkt+17, pktlen-17);
auth_proto = x11_identify_auth_proto(auth_proto_str);
sfree(auth_proto_str);
pos = 17 + getstring_size(pkt+17, pktlen-17);
auth_data = getstring(pkt+pos, pktlen-pos);
pos += getstring_size(pkt+pos, pktlen-pos);
if (pktlen < pos+4) {
err = dupprintf("Truncated CHANNEL_REQUEST(\"x11\") packet");
sfree(auth_data);
goto confused;
}
screen = GET_32BIT(pkt+pos);
if (auth_proto < 0) {
/* Reject due to not understanding downstream's
* requested authorisation method. */
unsigned char recipient_id[4];
PUT_32BIT(recipient_id, chan->downstream_id);
send_packet_to_downstream(cs, SSH2_MSG_CHANNEL_FAILURE,
recipient_id, 4, NULL);
sfree(auth_data);
break;
}
chan->x11_auth_proto = auth_proto;
chan->x11_auth_data = x11_dehexify(auth_data,
&chan->x11_auth_datalen);
sfree(auth_data);
chan->x11_auth_upstream =
ssh_sharing_add_x11_display(cs->parent->ssh, auth_proto,
cs, chan);
chan->x11_one_shot = single_connection;
/*
* Now construct a replacement X forwarding request,
* containing our own auth data, and send that to the
* server.
*/
protolen = strlen(chan->x11_auth_upstream->protoname);
datalen = strlen(chan->x11_auth_upstream->datastring);
pktlen = 29+protolen+datalen;
pkt = snewn(pktlen, unsigned char);
PUT_32BIT(pkt, server_id);
PUT_32BIT(pkt+4, 7); /* strlen("x11-req") */
memcpy(pkt+8, "x11-req", 7);
pkt[15] = want_reply;
pkt[16] = single_connection;
PUT_32BIT(pkt+17, protolen);
memcpy(pkt+21, chan->x11_auth_upstream->protoname, protolen);
PUT_32BIT(pkt+21+protolen, datalen);
memcpy(pkt+25+protolen, chan->x11_auth_upstream->datastring,
datalen);
PUT_32BIT(pkt+25+protolen+datalen, screen);
ssh_send_packet_from_downstream(cs->parent->ssh, cs->id,
SSH2_MSG_CHANNEL_REQUEST,
pkt, pktlen, NULL);
sfree(pkt);
break;
}
sfree(request_name);
}
ssh_send_packet_from_downstream(cs->parent->ssh, cs->id,
type, pkt, pktlen, NULL);
if (type == SSH2_MSG_CHANNEL_CLOSE && pktlen >= 4) {
server_id = GET_32BIT(pkt);
chan = share_find_channel_by_server(cs, server_id);
if (chan) {
if (chan->state == RCVD_CLOSE) {
ssh_delete_sharing_channel(cs->parent->ssh,
chan->upstream_id);
share_remove_channel(cs, chan);
} else {
chan->state = SENT_CLOSE;
}
}
}
break;
default:
err = dupprintf("Unexpected packet type %d\n", type);
goto confused;
/*
* Any other packet type is unexpected. In particular, we
* never pass GLOBAL_REQUESTs downstream, so we never expect
* to see SSH2_MSG_REQUEST_{SUCCESS,FAILURE}.
*/
confused:
assert(err != NULL);
share_disconnect(cs, err);
sfree(err);
break;
}
}
/*
* Coroutine macros similar to, but simplified from, those in ssh.c.
*/
#define crBegin(v) { int *crLine = &v; switch(v) { case 0:;
#define crFinish(z) } *crLine = 0; return (z); }
#define crGetChar(c) do \
{ \
while (len == 0) { \
*crLine =__LINE__; return 1; case __LINE__:; \
} \
len--; \
(c) = (unsigned char)*data++; \
} while (0)
static int share_receive(Plug plug, int urgent, char *data, int len)
{
struct ssh_sharing_connstate *cs = (struct ssh_sharing_connstate *)plug;
static const char expected_verstring_prefix[] =
"SSHCONNECTION@putty.projects.tartarus.org-2.0-";
unsigned char c;
crBegin(cs->crLine);
/*
* First read the version string from downstream.
*/
cs->recvlen = 0;
while (1) {
crGetChar(c);
if (c == '\012')
break;
if (cs->recvlen >= sizeof(cs->recvbuf)) {
char *buf = dupprintf("Version string far too long\n");
share_disconnect(cs, buf);
sfree(buf);
goto dead;
}
cs->recvbuf[cs->recvlen++] = c;
}
/*
* Now parse the version string to make sure it's at least vaguely
* sensible, and log it.
*/
if (cs->recvlen < sizeof(expected_verstring_prefix)-1 ||
memcmp(cs->recvbuf, expected_verstring_prefix,
sizeof(expected_verstring_prefix) - 1)) {
char *buf = dupprintf("Version string did not have expected prefix\n");
share_disconnect(cs, buf);
sfree(buf);
goto dead;
}
if (cs->recvlen > 0 && cs->recvbuf[cs->recvlen-1] == '\015')
cs->recvlen--; /* trim off \r before \n */
ssh_sharing_logf(cs->parent->ssh, cs->id,
"Downstream version string: %.*s",
cs->recvlen, cs->recvbuf);
/*
* Loop round reading packets.
*/
while (1) {
cs->recvlen = 0;
while (cs->recvlen < 4) {
crGetChar(c);
cs->recvbuf[cs->recvlen++] = c;
}
cs->curr_packetlen = toint(GET_32BIT(cs->recvbuf) + 4);
if (cs->curr_packetlen < 5 ||
cs->curr_packetlen > sizeof(cs->recvbuf)) {
char *buf = dupprintf("Bad packet length %u\n",
(unsigned)cs->curr_packetlen);
share_disconnect(cs, buf);
sfree(buf);
goto dead;
}
while (cs->recvlen < cs->curr_packetlen) {
crGetChar(c);
cs->recvbuf[cs->recvlen++] = c;
}
share_got_pkt_from_downstream(cs, cs->recvbuf[4],
cs->recvbuf + 5, cs->recvlen - 5);
}
dead:;
crFinish(1);
}
static void share_sent(Plug plug, int bufsize)
{
/* struct ssh_sharing_connstate *cs = (struct ssh_sharing_connstate *)plug; */
/*
* We do nothing here, because we expect that there won't be a
* need to throttle and unthrottle the connection to a downstream.
* It should automatically throttle itself: if the SSH server
* sends huge amounts of data on all channels then it'll run out
* of window until our downstream sends it back some
* WINDOW_ADJUSTs.
*/
}
static int share_listen_closing(Plug plug, const char *error_msg,
int error_code, int calling_back)
{
struct ssh_sharing_state *sharestate = (struct ssh_sharing_state *)plug;
if (error_msg)
ssh_sharing_logf(sharestate->ssh, 0,
"listening socket: %s", error_msg);
sk_close(sharestate->listensock);
sharestate->listensock = NULL;
return 1;
}
static void share_send_verstring(struct ssh_sharing_connstate *cs)
{
char *fullstring = dupcat("SSHCONNECTION@putty.projects.tartarus.org-2.0-",
cs->parent->server_verstring, "\015\012", NULL);
sk_write(cs->sock, fullstring, strlen(fullstring));
sfree(fullstring);
cs->sent_verstring = TRUE;
}
int share_ndownstreams(void *state)
{
struct ssh_sharing_state *sharestate = (struct ssh_sharing_state *)state;
return count234(sharestate->connections);
}
void share_activate(void *state, const char *server_verstring)
{
/*
* Indication from ssh.c that we are now ready to begin serving
* any downstreams that have already connected to us.
*/
struct ssh_sharing_state *sharestate = (struct ssh_sharing_state *)state;
struct ssh_sharing_connstate *cs;
int i;
/*
* Trim the server's version string down to just the software
* version component, removing "SSH-2.0-" or whatever at the
* front.
*/
for (i = 0; i < 2; i++) {
server_verstring += strcspn(server_verstring, "-");
if (*server_verstring)
server_verstring++;
}
sharestate->server_verstring = dupstr(server_verstring);
for (i = 0; (cs = (struct ssh_sharing_connstate *)
index234(sharestate->connections, i)) != NULL; i++) {
assert(!cs->sent_verstring);
share_send_verstring(cs);
}
}
static int share_listen_accepting(Plug plug,
accept_fn_t constructor, accept_ctx_t ctx)
{
static const struct plug_function_table connection_fn_table = {
NULL, /* no log function, because that's for outgoing connections */
share_closing,
share_receive,
share_sent,
NULL /* no accepting function, because we've already done it */
};
struct ssh_sharing_state *sharestate = (struct ssh_sharing_state *)plug;
struct ssh_sharing_connstate *cs;
const char *err;
/*
* A new downstream has connected to us.
*/
cs = snew(struct ssh_sharing_connstate);
cs->fn = &connection_fn_table;
cs->parent = sharestate;
if ((cs->id = share_find_unused_id(sharestate, sharestate->nextid)) == 0 &&
(cs->id = share_find_unused_id(sharestate, 1)) == 0) {
sfree(cs);
return 1;
}
sharestate->nextid = cs->id + 1;
if (sharestate->nextid == 0)
sharestate->nextid++; /* only happens in VERY long-running upstreams */
cs->sock = constructor(ctx, (Plug) cs);
if ((err = sk_socket_error(cs->sock)) != NULL) {
sfree(cs);
return err != NULL;
}
sk_set_frozen(cs->sock, 0);
add234(cs->parent->connections, cs);
cs->sent_verstring = FALSE;
if (sharestate->server_verstring)
share_send_verstring(cs);
cs->got_verstring = FALSE;
cs->recvlen = 0;
cs->crLine = 0;
cs->halfchannels = newtree234(share_halfchannel_cmp);
cs->channels_by_us = newtree234(share_channel_us_cmp);
cs->channels_by_server = newtree234(share_channel_server_cmp);
cs->xchannels_by_us = newtree234(share_xchannel_us_cmp);
cs->xchannels_by_server = newtree234(share_xchannel_server_cmp);
cs->forwardings = newtree234(share_forwarding_cmp);
cs->globreq_head = cs->globreq_tail = NULL;
ssh_sharing_downstream_connected(sharestate->ssh, cs->id);
return 0;
}
/* Per-application overrides for what roles we can take (e.g. pscp
* will never be an upstream) */
extern const int share_can_be_downstream;
extern const int share_can_be_upstream;
/*
* Init function for connection sharing. We either open a listening
* socket and become an upstream, or connect to an existing one and
* become a downstream, or do neither. We are responsible for deciding
* which of these to do (including checking the Conf to see if
* connection sharing is even enabled in the first place). If we
* become a downstream, we return the Socket with which we connected
* to the upstream; otherwise (whether or not we have established an
* upstream) we return NULL.
*/
Socket ssh_connection_sharing_init(const char *host, int port,
Conf *conf, Ssh ssh, void **state)
{
static const struct plug_function_table listen_fn_table = {
NULL, /* no log function, because that's for outgoing connections */
share_listen_closing,
NULL, /* no receive function on a listening socket */
NULL, /* no sent function on a listening socket */
share_listen_accepting
};
int result, can_upstream, can_downstream;
char *logtext, *ds_err, *us_err;
char *sockname;
Socket sock;
struct ssh_sharing_state *sharestate;
if (!conf_get_int(conf, CONF_ssh_connection_sharing))
return NULL; /* do not share anything */
can_upstream = share_can_be_upstream &&
conf_get_int(conf, CONF_ssh_connection_sharing_upstream);
can_downstream = share_can_be_downstream &&
conf_get_int(conf, CONF_ssh_connection_sharing_downstream);
if (!can_upstream && !can_downstream)
return NULL;
/*
* Decide on the string used to identify the connection point
* between upstream and downstream (be it a Windows named pipe or
* a Unix-domain socket or whatever else).
*
* I wondered about making this a SHA hash of all sorts of pieces
* of the PuTTY configuration - essentially everything PuTTY uses
* to know where and how to make a connection, including all the
* proxy details (or rather, all the _relevant_ ones - only
* including settings that other settings didn't prevent from
* having any effect), plus the username. However, I think it's
* better to keep it really simple: the connection point
* identifier is derived from the hostname and port used to index
* the host-key cache (not necessarily where we _physically_
* connected to, in cases involving proxies or CONF_loghost), plus
* the username if one is specified.
*/
{
char *username = get_remote_username(conf);
if (port == 22) {
if (username)
sockname = dupprintf("%s@%s", username, host);
else
sockname = dupprintf("%s", host);
} else {
if (username)
sockname = dupprintf("%s@%s:%d", username, host, port);
else
sockname = dupprintf("%s:%d", host, port);
}
sfree(username);
/*
* The platform-specific code may transform this further in
* order to conform to local namespace conventions (e.g. not
* using slashes in filenames), but that's its job and not
* ours.
*/
}
/*
* Create a data structure for the listening plug if we turn out
* to be an upstream.
*/
sharestate = snew(struct ssh_sharing_state);
sharestate->fn = &listen_fn_table;
sharestate->listensock = NULL;
/*
* Now hand off to a per-platform routine that either connects to
* an existing upstream (using 'ssh' as the plug), establishes our
* own upstream (using 'sharestate' as the plug), or forks off a
* separate upstream and then connects to that. It will return a
* code telling us which kind of socket it put in 'sock'.
*/
sock = NULL;
logtext = ds_err = us_err = NULL;
result = platform_ssh_share(sockname, conf, (Plug)ssh,
(Plug)sharestate, &sock, &logtext, &ds_err,
&us_err, can_upstream, can_downstream);
ssh_connshare_log(ssh, result, logtext, ds_err, us_err);
sfree(logtext);
sfree(ds_err);
sfree(us_err);
switch (result) {
case SHARE_NONE:
/*
* We aren't sharing our connection at all (e.g. something
* went wrong setting the socket up). Free the upstream
* structure and return NULL.
*/
assert(sock == NULL);
*state = NULL;
sfree(sharestate);
sfree(sockname);
return NULL;
case SHARE_DOWNSTREAM:
/*
* We are downstream, so free sharestate which it turns out we
* don't need after all, and return the downstream socket as a
* replacement for an ordinary SSH connection.
*/
*state = NULL;
sfree(sharestate);
sfree(sockname);
return sock;
case SHARE_UPSTREAM:
/*
* We are upstream. Set up sharestate properly and pass a copy
* to the caller; return NULL, to tell ssh.c that it has to
* make an ordinary connection after all.
*/
*state = sharestate;
sharestate->listensock = sock;
sharestate->connections = newtree234(share_connstate_cmp);
sharestate->ssh = ssh;
sharestate->server_verstring = NULL;
sharestate->sockname = sockname;
sharestate->nextid = 1;
return NULL;
}
return NULL;
}
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