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Relaxed Channel Join PDU requirements for non-TLS

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Windows 10 RDS is quite relaxed about missing channel join PDUs,
whereas we have to adhere quite tightly to the specification to
make sure we get a TLS "Client hello" where appropriate. This makes
us incompatible with older RDP clients. For example, the Wyse sx0
thin client does not send a channel join PDU for the user channel.
Older, non-TLS versions of xrdp supported these devices.

This commit re-implements the xrdp v0.6.1 behaviour for non-TLS
connections only, allowing system administrators to use these devices
on trusted networks. These devices are in any case too old to
establish a modern TLS connection.
This commit is contained in:
matt335672
2022-05-12 16:04:54 +01:00
parent 6838643494
commit 8fdc1ba216
2 changed files with 190 additions and 77 deletions
Download Patch File Download Diff File Expand all files Collapse all files
libxrdp/xrdp_mcs.c
+187 -77
View File
@@ -27,6 +27,11 @@
#include "ms-rdpbcgr.h"
#include "log.h"
/* Forward references */
static int
handle_non_tls_client_channel_join_requests(struct xrdp_mcs *self,
struct stream *s, int *appid);
/*****************************************************************************/
struct xrdp_mcs *
xrdp_mcs_create(struct xrdp_sec *owner, struct trans *trans,
@@ -123,6 +128,34 @@ xrdp_mcs_send_cjcf(struct xrdp_mcs *self, int userid, int chanid)
return 0;
}
/*****************************************************************************/
/* Reads the header of a DomainMCSPDU and gets the appid
*
* @return 0 for success */
static int
get_domain_mcs_pdu_header(struct xrdp_mcs *self, struct stream *s, int *appid)
{
int opcode;
if (xrdp_iso_recv(self->iso_layer, s) != 0)
{
LOG(LOG_LEVEL_ERROR, "xrdp_mcs_recv: xrdp_iso_recv failed");
return 1;
}
if (!s_check_rem_and_log(s, 1, "Parsing [ITU-T T.125] DomainMCSPDU"))
{
return 1;
}
/* The DomainMCSPDU choice index is a 6-bit int with the 2 least
significant bits of the byte as padding */
in_uint8(s, opcode);
*appid = opcode >> 2; /* 2-bit padding */
LOG_DEVEL(LOG_LEVEL_TRACE,
"Received [ITU-T T.125] DomainMCSPDU choice index %d", *appid);
return 0;
}
/*****************************************************************************/
/*
* Processes an [ITU-T T.125] DomainMCSPDU message.
@@ -136,70 +169,32 @@ int
xrdp_mcs_recv(struct xrdp_mcs *self, struct stream *s, int *chan)
{
int appid;
int opcode;
int len;
int userid;
int chanid;
while (1)
if (get_domain_mcs_pdu_header(self, s, &appid) != 0)
{
if (xrdp_iso_recv(self->iso_layer, s) != 0)
{
LOG(LOG_LEVEL_ERROR, "xrdp_mcs_recv: xrdp_iso_recv failed");
return 1;
}
if (!s_check_rem_and_log(s, 1, "Parsing [ITU-T T.125] DomainMCSPDU"))
{
return 1;
}
/* The DomainMCSPDU choice index is a 6-bit int with the 2 least
significant bits of the byte as padding */
in_uint8(s, opcode);
appid = opcode >> 2; /* 2-bit padding */
LOG_DEVEL(LOG_LEVEL_TRACE,
"Received [ITU-T T.125] DomainMCSPDU choice index %d", appid);
if (appid == MCS_DPUM) /* Disconnect Provider Ultimatum */
{
LOG_DEVEL(LOG_LEVEL_TRACE, "Received [ITU-T T.125] DisconnectProviderUltimatum");
LOG(LOG_LEVEL_DEBUG, "Recieved disconnection request");
return 1;
}
/* MCS_CJRQ: Channel Join ReQuest
this is channels getting added from the client */
if (appid == MCS_CJRQ)
{
if (!s_check_rem_and_log(s, 4, "Parsing [ITU-T T.125] ChannelJoinRequest"))
{
return 1;
}
in_uint16_be(s, userid);
in_uint16_be(s, chanid);
LOG_DEVEL(LOG_LEVEL_TRACE, "Received [ITU-T T.125] ChannelJoinRequest "
"initiator 0x%4.4x, channelId 0x%4.4x", userid, chanid);
if (xrdp_mcs_send_cjcf(self, userid, chanid) != 0)
{
LOG(LOG_LEVEL_WARNING, "[ITU-T T.125] Channel join sequence: failed");
}
s = libxrdp_force_read(self->iso_layer->trans);
if (s == 0)
{
LOG(LOG_LEVEL_ERROR, "xrdp_mcs_recv: libxrdp_force_read failed");
return 1;
}
continue;
}
break;
return 1;
}
if (self->expecting_channel_join_requests)
{
if (handle_non_tls_client_channel_join_requests(self, s, &appid) != 0)
{
return 1;
}
LOG(LOG_LEVEL_DEBUG, "[MCS Connection Sequence] completed");
self->expecting_channel_join_requests = 0;
}
if (appid == MCS_DPUM) /* Disconnect Provider Ultimatum */
{
LOG_DEVEL(LOG_LEVEL_TRACE,
"Received [ITU-T T.125] DisconnectProviderUltimatum");
LOG(LOG_LEVEL_DEBUG, "Recieved disconnection request");
return 1;
}
if (appid != MCS_SDRQ)
{
LOG(LOG_LEVEL_ERROR, "Received [ITU-T T.125] DomainMCSPDU "
@@ -1176,6 +1171,127 @@ xrdp_mcs_send_connect_response(struct xrdp_mcs *self)
return 0;
}
/*****************************************************************************/
/* Handle all client channel join requests for a non-TLS connection
*
* @param self MCS structure
* @param s Input stream
* @param[in,out] appid Type of the MCS PDU whose header has just been read.
* @return 0 for success
*
* For non-TLS connections, the channel join MCS PDUs are followed by
* another MCS PDU. This not the case for TLS connections.
*
* Called when an MCS PDU header has been read, but the PDU has not
* been processed.
*
* If the PDU is a channel join request, it is processed, and the next
* PDU header is read. When we've exhausted all the channel join requests,
* the type of the next PDU is passed back to the caller for the caller
* to process.
*
* In order to cater for older clients which may not conform exactly to
* the specification, we simply take all the join requests which come in,
* and respond to them.
*
* See :-
* - https://github.com/neutrinolabs/xrdp/issues/2166
* - [MS-RDPBCGR] 3.2.5.3.8 and 3.2.5.3.8
*/
static int
handle_non_tls_client_channel_join_requests(struct xrdp_mcs *self,
struct stream *s, int *appid)
{
int rv = 0;
while (*appid == MCS_CJRQ)
{
int userid;
int chanid;
if (!s_check_rem_and_log(s, 4, "Parsing [ITU-T T.125] "
"ChannelJoinRequest"))
{
rv = 1;
break;
}
in_uint16_be(s, userid);
in_uint16_be(s, chanid);
LOG_DEVEL(LOG_LEVEL_TRACE,
"Received [ITU-T T.125] ChannelJoinRequest "
"initiator 0x%4.4x, channelId 0x%4.4x", userid, chanid);
if (xrdp_mcs_send_cjcf(self, userid, chanid) != 0)
{
LOG(LOG_LEVEL_WARNING,
"[ITU-T T.125] Channel join sequence: failed");
}
/* Get the next PDU header */
s = libxrdp_force_read(self->iso_layer->trans);
if (s == 0)
{
LOG(LOG_LEVEL_ERROR, "xrdp_mcs_recv: libxrdp_force_read failed");
rv = 1;
break;
}
if (get_domain_mcs_pdu_header(self, s, appid) != 0)
{
rv = 1;
break;
}
}
return rv;
}
/*****************************************************************************/
/* Handle all client channel join requests for a TLS connection
*
* @param self MCS structure
* @return 0 for success
*
* When were are about to negotiate a TLS connection, it is important that
* we agree on the exact number of client join request / client join confirm
* PDUs, so that we get the TLS 'client hello' message exactly when
* expected.
*
* See [MS-RDPBCGR] 3.2.5.3.8 and 3.2.5.3.8
*/
static int
handle_tls_client_channel_join_requests(struct xrdp_mcs *self)
{
int index;
int rv = 0;
static const char *tag = "[MCS Connection Sequence (TLS)]";
/*
* Expect a channel join request PDU for each of the static virtual
* channels, plus the user channel (self->chanid) and the I/O channel
* (MCS_GLOBAL_CHANNEL) */
for (index = 0; index < self->channel_list->count + 2; index++)
{
int channel_id;
LOG(LOG_LEVEL_DEBUG, "%s receive channel join request", tag);
if (xrdp_mcs_recv_cjrq(self, &channel_id) != 0)
{
LOG(LOG_LEVEL_ERROR, "%s receive channel join request failed", tag);
rv = 1;
break;
}
LOG(LOG_LEVEL_DEBUG, "%s send channel join confirm", tag);
if (xrdp_mcs_send_cjcf(self, self->userid, channel_id) != 0)
{
LOG(LOG_LEVEL_ERROR, "%s send channel join confirm failed", tag);
rv = 1;
break;
}
}
return rv;
}
/*****************************************************************************/
/* Process and send the MCS messages for the RDP Connection Sequence
* [MS-RDPBCGR] 1.3.1.1
@@ -1185,8 +1301,6 @@ xrdp_mcs_send_connect_response(struct xrdp_mcs *self)
int
xrdp_mcs_incoming(struct xrdp_mcs *self)
{
int index;
LOG(LOG_LEVEL_DEBUG, "[MCS Connection Sequence] receive connection request");
if (xrdp_mcs_recv_connect_initial(self) != 0)
{
@@ -1236,29 +1350,25 @@ xrdp_mcs_incoming(struct xrdp_mcs *self)
return 1;
}
/*
* Expect a channel join request PDU for each of the static virtual channels, plus
* the user channel (self->chanid) and the I/O channel (MCS_GLOBAL_CHANNEL)
*/
for (index = 0; index < self->channel_list->count + 2; index++)
if (self->iso_layer->selectedProtocol > PROTOCOL_RDP)
{
int channel_id;
LOG(LOG_LEVEL_DEBUG, "[MCS Connection Sequence] receive channel join request");
if (xrdp_mcs_recv_cjrq(self, &channel_id) != 0)
/* TLS connection. Client and server have to agree on MCS channel
* join messages, and these have to be processed before the TLS
* client hello */
if (handle_tls_client_channel_join_requests(self) != 0)
{
LOG(LOG_LEVEL_ERROR, "[MCS Connection Sequence] receive channel join request failed");
return 1;
}
LOG(LOG_LEVEL_DEBUG, "[MCS Connection Sequence] send channel join confirm");
if (xrdp_mcs_send_cjcf(self, self->userid, channel_id) != 0)
{
LOG(LOG_LEVEL_ERROR, "[MCS Connection Sequence] send channel join confirm failed");
return 1;
}
LOG(LOG_LEVEL_DEBUG, "[MCS Connection Sequence (TLS)] completed");
}
else
{
/* Non-TLS connection - channel joins handled in MCS PDU
* processing loop */
self->expecting_channel_join_requests = 1;
}
LOG(LOG_LEVEL_DEBUG, "[MCS Connection Sequence] completed");
return 0;
}