Add sesexec control module
This module provides a secure way for sesman to start the sesexec program and establish a private communications channel with it.
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matt335672
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3d95954d87
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dadb393443
@ -24,6 +24,8 @@ xrdp_sesman_SOURCES = \
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scp_process.h \
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sesman.c \
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sesman.h \
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sesexec_control.c \
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sesexec_control.h \
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session.c \
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session.h \
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session_list.c \
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228
sesman/sesexec_control.c
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228
sesman/sesexec_control.c
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@ -0,0 +1,228 @@
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/**
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* xrdp: A Remote Desktop Protocol server.
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*
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* Copyright (C) 2023 Matt Burt
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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/**
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*
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* @file sesexec_control.c
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* @brief Start/stop session executive process
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* @author Matt Burt
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*
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*/
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#if defined(HAVE_CONFIG_H)
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#include <config_ac.h>
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#endif
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#include "sesman_config.h"
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#include "eicp.h"
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#include "log.h"
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#include "os_calls.h"
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#include "pre_session_list.h"
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#include "string_calls.h"
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#include "sesexec_control.h"
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#include "sesman.h"
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#include "trans.h"
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#include "xrdp_sockets.h"
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#define SESEXEC_SHORTNAME "xrdp-sesexec"
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#define SESEXEC_LONGNAME XRDP_LIBEXEC_PATH "/" SESEXEC_SHORTNAME
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// Some platforms using setsid() benefit from sesexec being
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// forked again, so the UNIX session can be created cleanly
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// See FreeBSD bug
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// ports/157282: effective login name is not set by xrdp-sesman
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// https://www.freebsd.org/cgi/query-pr.cgi?pr=157282
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#if defined(__FreeBSD__) || defined(__FreeBSD_kernel__)
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#define USE_BSD_SETLOGIN 1
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#endif
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/*****************************************************************************/
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/**
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* Adds entries to the args list for running sesexec
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*
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* @param args Argument list
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* @return 0 for memory allocation failure, 1 for success
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*/
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static int
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create_exec_args_add_entries(struct list *args)
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{
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if (!list_add_strdup(args, SESEXEC_SHORTNAME))
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{
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return 0;
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}
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if (g_strcmp(g_cfg->sesman_ini, DEFAULT_SESMAN_INI) != 0)
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{
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if (!list_add_strdup_multi(args, "-c", g_cfg->sesman_ini, NULL))
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{
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return 0;
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}
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}
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return 1;
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}
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/*****************************************************************************/
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/**
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* Create an args list for sesexec
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* @return NULL if memory could not be allocated
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*
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* The result must be freed with list_delete() after use
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*/
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static struct list *
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create_exec_args(void)
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{
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struct list *result = list_create();
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if (result != NULL)
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{
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result->auto_free = 1;
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if (!create_exec_args_add_entries(result))
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{
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list_delete(result);
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result = NULL;
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}
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}
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return result;
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}
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/*****************************************************************************/
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int
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sesexec_start(struct pre_session_item *psi)
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{
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// Local socket pair used to set up the EICP channel for sesexec
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// We also use the socket pair to communicate the PID of sesexec back
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// to sesman. Technically we only need this if USE_BSD_SETLOGIN
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// is set, but removing this variable complicates the code so
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// much it isn't worth it.
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int sck[2] = {-1, -1};
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int rv = -1;
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int size;
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const char *exe = SESEXEC_LONGNAME;
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struct list *args = NULL;
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if (!g_executable_exist(exe))
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{
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LOG(LOG_LEVEL_ERROR, "Can't execute %s", exe);
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}
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else if ((args = create_exec_args()) == NULL)
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{
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LOG(LOG_LEVEL_ERROR, "Out of memory running sesexec");
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}
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else if (g_sck_local_socketpair(sck) < 0)
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{
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LOG(LOG_LEVEL_ERROR, "Can't create sesexec EICP socket [%s]",
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g_get_strerror());
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}
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else
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{
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int pid = g_fork();
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if (pid == -1)
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{
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// Error already logged
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g_file_close(sck[0]);
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g_file_close(sck[1]);
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}
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else if (pid == 0)
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{
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/* Sesexec process */
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g_file_close(sck[0]);
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#if USE_BSD_SETLOGIN
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if (g_fork() != 0)
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{
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g_exit(0);
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}
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#endif
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// Send our pid back to sesman
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pid = g_getpid();
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size = g_file_write(sck[1], (const char *)&pid, sizeof(pid));
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if (size != sizeof(pid))
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{
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LOG(LOG_LEVEL_ERROR, "Can't write to PID socket [%s]",
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g_get_strerror());
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}
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else
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{
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/* Put the number of the file descriptor in EICP_FD
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* in the environment */
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char buff[64];
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g_snprintf(buff, sizeof(buff), "%d", sck[1]);
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g_setenv("EICP_FD", buff, 1);
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/* [Development] Log all file descriptors not marked cloexec
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* other than stdin, stdout, stderr, and the EICP fd in sck[1].
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*/
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if (sck[1] < 3)
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{
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// EICP fd has overwritten one of the standard descriptors
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LOG_DEVEL_LEAKING_FDS("xrdp-sesexec", 3, -1);
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}
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else
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{
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LOG_DEVEL_LEAKING_FDS("xrdp-sesexec", 3, sck[1]);
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LOG_DEVEL_LEAKING_FDS("xrdp-sesexec", sck[1] + 1, -1);
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}
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g_execvp_list(exe, args);
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// Shouldn't get here. Errors are logged if we do.
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}
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g_exit(1);
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}
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else
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{
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g_file_close(sck[1]);
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// Get the PID from the child (or the grancdchild)
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int size = g_file_read(sck[0], (char *)&pid, sizeof(pid));
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if (size != sizeof(pid))
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{
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LOG(LOG_LEVEL_ERROR, "Can't read PID of sesexec process [%s]",
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g_get_strerror());
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g_file_close(sck[0]);
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}
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else
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{
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struct trans *t = eicp_init_trans_from_fd(sck[0],
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TRANS_TYPE_CLIENT,
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sesman_is_term);
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if (t == NULL)
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{
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LOG(LOG_LEVEL_ERROR, "Can't create sesexec transport [%s]",
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g_get_strerror());
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g_file_close(sck[0]);
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}
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else
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{
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t->trans_data_in = sesman_eicp_data_in;
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t->callback_data = (void *)psi;
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psi->sesexec_trans = t;
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psi->sesexec_pid = pid;
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rv = 0;
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}
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}
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}
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}
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list_delete(args);
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return rv;
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}
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49
sesman/sesexec_control.h
Normal file
49
sesman/sesexec_control.h
Normal file
@ -0,0 +1,49 @@
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/**
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* xrdp: A Remote Desktop Protocol server.
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*
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* Copyright (C) 2023 Matt Burt
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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/**
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*
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* @file sesexec_control.h
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* @brief Start/stop session executive process
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* @author Matt Burt
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*
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*/
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#ifndef SESEXEC_H
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#define SESEXEC_H
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#include <sys/types.h>
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struct trans;
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struct pre_session_item;
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/**
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* Start a session executive
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* @param psi Pre-session item to allocate EICP transport to
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* @result 0 for success
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*
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* If non-zero is returned, all errors have been logged.
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* If zero is returned, the sesexec_trans and sesexec_pid fields of
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* the pre-session-item have been initialised.
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*/
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int
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sesexec_start(struct pre_session_item *psi);
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#endif // SESEXEC_H
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