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Rework the start session method in SCP

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The start session method is reworked to pass a response back to the
client.
If the method was successful, a session list entry is created. This
is different to the provious behaviour, where we created the
session list entry unconditionally.

This new arrangement means that we need a different way to avoid
a race condition where two users may try to create a session at the
same time, and end up with the same display. We do this by keeping
track of newly allocated displays as part of the SCP connections. When
we allocate a display, the SCP connection displays are also taken
into account.
This commit is contained in:
matt335672
2025-06-10 11:06:20 +01:00
parent 7baa27a59f
commit 3e38d9be80
17 changed files with 604 additions and 328 deletions
Download Patch File Download Diff File Expand all files Collapse all files
sesman/scp_process.c
+69 -59
View File
@@ -31,15 +31,16 @@
#include "trans.h"
#include "os_calls.h"
#include "eicp.h"
#include "ercp.h"
#include "scp.h"
#include "display_utils.h"
#include "scp_process.h"
#include "sesman.h"
#include "sesman_access.h"
#include "sesman_auth.h"
#include "sesman_config.h"
#include "os_calls.h"
#include "set_int.h"
#include "scp_list.h"
#include "session_list.h"
#include "sesexec_control.h"
@@ -389,13 +390,45 @@ create_xrdp_socket_path(uid_t uid)
#undef RWX_PERMS
}
/******************************************************************************/
/*
* Gets a free display number
*
* We can't use displays either allocated to sessions, or being used to
* create sessions
*/
static int
get_free_display(void)
{
int result = -1;
struct set_int *alloc_displays;
alloc_displays = set_int_init(g_cfg->sess.x11_display_offset,
g_cfg->sess.max_display_number);
if (alloc_displays != NULL)
{
// Get all the displays either allocated to sessions, or
// potentially assigned to sessions on the SCP list
session_list_get_session_displays(alloc_displays);
scp_list_get_create_session_displays(alloc_displays);
// Find a free display, taking the allocated ones into account
result = display_utils_get_free_display(alloc_displays);
set_int_delete(alloc_displays);
}
return result;
}
/******************************************************************************/
static int
process_create_session_request(struct scp_list_item *sli)
{
int rv;
/* Client parameters describing new session*/
/* Client parameters describing new session */
enum scp_session_type type;
unsigned short width;
unsigned short height;
@@ -404,8 +437,9 @@ process_create_session_request(struct scp_list_item *sli)
const char *directory;
struct guid guid;
int display = 0;
int display = -1;
struct session_item *s_item = NULL;
int start_sesexec = (sli->sesexec_trans == NULL);
int send_client_reply = 1;
enum scp_screate_status status = E_SCP_SCREATE_OK;
@@ -420,6 +454,10 @@ process_create_session_request(struct scp_list_item *sli)
{
status = E_SCP_SCREATE_NOT_LOGGED_IN;
}
else if (sli->create_session_in_progress)
{
status = E_SCP_SCREATE_IN_PROGRESS;
}
else
{
LOG(LOG_LEVEL_INFO,
@@ -433,29 +471,6 @@ process_create_session_request(struct scp_list_item *sli)
// Found an existing session
display = s_item->display;
guid = s_item->guid;
// Tell the existing session to run the reconnect script.
// We ignore errors at this level, as any comms errors
// will be picked up in the main loop
(void)ercp_send_session_reconnect_event(s_item->sesexec_trans);
if (sli->start_ip_addr[0] != '\0')
{
LOG( LOG_LEVEL_INFO, "++ reconnected session: username %s, "
"display :%d.0, session_pid %d, ip %s",
sli->username, display,
s_item->sesexec_pid, sli->start_ip_addr);
}
else
{
LOG(LOG_LEVEL_INFO, "++ reconnected session: username %s, "
"display :%d.0, session_pid %d",
sli->username, display, s_item->sesexec_pid);
}
// If we created an authentication process for this SCP
// connection, close it gracefully
logout_scp_list_item(sli);
}
// Need to create a new session
else if (g_cfg->sess.max_sessions > 0 &&
@@ -463,34 +478,42 @@ process_create_session_request(struct scp_list_item *sli)
{
status = E_SCP_SCREATE_MAX_REACHED;
}
else if ((display = session_list_get_available_display()) < 0)
else if ((display = get_free_display()) < 0)
{
status = E_SCP_SCREATE_NO_DISPLAY;
}
// Create an entry on the session list for the new session
else if ((s_item = session_list_new()) == NULL)
{
status = E_SCP_SCREATE_NO_MEMORY;
}
// Create a socket dir for this user
else if (create_xrdp_socket_path(sli->uid) != 0)
{
status = E_SCP_SCREATE_GENERAL_ERROR;
}
// Create a sesexec process if we don't have one (UDS login)
else if (sli->sesexec_trans == NULL && sesexec_start(sli) != 0)
else if (start_sesexec && sesexec_start(sli) != 0)
{
LOG(LOG_LEVEL_ERROR,
"Can't start sesexec to manage session");
status = E_SCP_SCREATE_GENERAL_ERROR;
}
else if (start_sesexec &&
eicp_send_uds_login_request(
sli->sesexec_trans, sli->client_trans->sck) != 0)
{
// Because we started sesexec late, we needed to log it in.
// That hasn't gone too well.
LOG(LOG_LEVEL_ERROR,
"Can't set UID for sesexec process");
status = E_SCP_SCREATE_GENERAL_ERROR;
// Looks like sesexec is broken...
trans_delete(sli->sesexec_trans);
sli->sesexec_trans = NULL;
}
else
{
// Pass the session create request to sesexec
int eicp_stat;
eicp_stat = eicp_send_create_session_request(
sli->sesexec_trans,
sli->client_trans->sck,
display,
type, width, height,
bpp, shell, directory);
@@ -498,42 +521,29 @@ process_create_session_request(struct scp_list_item *sli)
if (eicp_stat != 0)
{
LOG(LOG_LEVEL_ERROR,
"Can't ask sesexec to authenticate user");
"Can't ask sesexec to create a session");
status = E_SCP_SCREATE_GENERAL_ERROR;
// Looks like sesexec is broken...
trans_delete(sli->sesexec_trans);
sli->sesexec_trans = NULL;
}
else
{
// We've handed over responsibility for the
// SCP communication
// We're not sending a reply yet
send_client_reply = 0;
// Further comms from sesexec comes over the ERCP
// protocol
ercp_trans_from_eicp_trans(sli->sesexec_trans,
sesman_ercp_data_in,
(void *)s_item);
// Move the transport over to the session list item
s_item->sesexec_trans = sli->sesexec_trans;
s_item->sesexec_pid = sli->sesexec_pid;
sli->sesexec_trans = NULL;
sli->sesexec_pid = 0;
// Add the display to the session item so we don't try
// to allocate it to another session
s_item->display = display;
sli->create_session_in_progress = 1;
sli->session_display = display; // Reserve display
}
}
}
// Currently a create session request is the last thing on a
// connection, and results in automatic closure
//
// We may have passed the client_trans over to sesexec. If so,
// we can't send a reply here.
sli->dispatcher_action = E_SLD_TERMINATE_SCP_CONN;
if (send_client_reply)
{
if (status != E_SCP_SCREATE_OK)
{
display = -1;
guid_clear(&guid);
}
rv = scp_send_create_session_response(sli->client_trans,
status, display, &guid);
}