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xrdp/xrdpapi/xrdp-ssh-agent.c

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/**
* xrdp: A Remote Desktop Protocol server.
*
* Copyright (C) Jay Sorg 2012-2013
* Copyright (C) Laxmikant Rashinkar 2012-2013
* Copyright (C) Ben Cohen 2017
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/*
* Portions are from OpenSSH, under the following license:
*
* Author: Tatu Ylonen <ylo@cs.hut.fi>
* Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
* All rights reserved
* The authentication agent program.
*
* As far as I am concerned, the code I have written for this software
* can be used freely for any purpose. Any derived versions of this
* software must be clearly marked as such, and if the derived work is
* incompatible with the protocol description in the RFC file, it must be
* called by a name other than "ssh" or "Secure Shell".
*
* Copyright (c) 2000, 2001 Markus Friedl. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
/*
* xrdp-ssh-agent.c: program to forward ssh-agent protocol from xrdp session
*
* This performs the equivalent function of ssh-agent on a server you connect
* to via ssh, but the ssh-agent protocol is over an RDP dynamic virtual
* channel and not an SSH channel.
*
* This will print out variables to set in your environment (specifically,
* $SSH_AUTH_SOCK) for ssh clients to find the agent's socket, then it will
* run in the background. This is suitable to run just as you would run the
* normal ssh-agent, e.g. in your Xsession or /etc/xrdp/startwm.sh.
*
* Your RDP client needs to be running a compatible client-side plugin
* that can see a local ssh-agent.
*
* usage (from within an xrdp session):
* xrdp-ssh-agent
*
* build instructions:
* gcc xrdp-ssh-agent.c -o xrdp-ssh-agent -L./.libs -lxrdpapi -Wall
*
* protocol specification:
* Forward data verbatim over RDP dynamic virtual channel named "sshagent"
* between a ssh client on the xrdp server and the real ssh-agent where
* the RDP client is running. Each connection by a separate client to
* xrdp-ssh-agent gets a separate DVC invocation.
*/
#if defined(HAVE_CONFIG_H)
#include <config_ac.h>
#endif
#ifdef __WIN32__
#include <mstsapi.h>
#endif
#include "xrdpapi.h"
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <sys/stat.h>
#include <linux/limits.h>
#include <fcntl.h>
#include <sys/time.h>
#include <sys/resource.h>
#include <poll.h>
#define _PATH_DEVNULL "/dev/null"
char socket_name[PATH_MAX];
char socket_dir[PATH_MAX];
static int sa_uds_fd = -1;
static int is_going = 1;
/* Make a template filename for mk[sd]temp() */
/* This is from mktemp_proto() in misc.c from openssh */
void
mktemp_proto(char *s, size_t len)
{
const char *tmpdir;
int r;
if ((tmpdir = getenv("TMPDIR")) != NULL)
{
r = snprintf(s, len, "%s/ssh-XXXXXXXXXXXX", tmpdir);
if (r > 0 && (size_t)r < len)
{
return;
}
}
r = snprintf(s, len, "/tmp/ssh-XXXXXXXXXXXX");
if (r < 0 || (size_t)r >= len)
{
fprintf(stderr, "%s: template string too short", __func__);
exit(1);
}
}
/* This uses parts of main() in ssh-agent.c from openssh */
static void
setup_ssh_agent(struct sockaddr_un *addr)
{
int rc;
/* Create private directory for agent socket */
mktemp_proto(socket_dir, sizeof(socket_dir));
if (mkdtemp(socket_dir) == NULL)
{
perror("mkdtemp: private socket dir");
exit(1);
}
snprintf(socket_name, sizeof socket_name, "%s/agent.%ld", socket_dir,
(long)getpid());
/* Create unix domain socket */
unlink(socket_name);
sa_uds_fd = socket(AF_UNIX, SOCK_STREAM, 0);
if (sa_uds_fd == -1)
{
fprintf(stderr, "sshagent: socket creation failed");
exit(2);
}
memset(addr, 0, sizeof(struct sockaddr_un));
addr->sun_family = AF_UNIX;
strncpy(addr->sun_path, socket_name, sizeof(addr->sun_path));
addr->sun_path[sizeof(addr->sun_path) - 1] = 0;
/* Create with privileges rw------- so other users can't access the UDS */
mode_t umask_sav = umask(0177);
rc = bind(sa_uds_fd, (struct sockaddr *)addr, sizeof(struct sockaddr_un));
if (rc != 0)
{
fprintf(stderr, "sshagent: bind failed");
close(sa_uds_fd);
unlink(socket_name);
exit(3);
}
umask(umask_sav);
rc = listen(sa_uds_fd, /* backlog = */ 5);
if (rc != 0)
{
fprintf(stderr, "listen failed\n");
close(sa_uds_fd);
unlink(socket_name);
exit(1);
}
/* Now fork: the child becomes the ssh-agent daemon and the parent prints
* out the pid and socket name. */
pid_t pid = fork();
if (pid == -1)
{
perror("fork");
exit(1);
}
else if (pid != 0)
{
/* Parent */
close(sa_uds_fd);
printf("SSH_AUTH_SOCK=%s; export SSH_AUTH_SOCK;\n", socket_name);
printf("SSH_AGENT_PID=%d; export SSH_AGENT_PID;\n", pid);
printf("echo Agent pid %d;\n", pid);
exit(0);
}
/* Child */
if (setsid() == -1)
{
fprintf(stderr, "setsid failed");
exit(1);
}
(void)chdir("/");
int devnullfd;
if ((devnullfd = open(_PATH_DEVNULL, O_RDWR, 0)) != -1)
{
/* XXX might close listen socket */
(void)dup2(devnullfd, STDIN_FILENO);
(void)dup2(devnullfd, STDOUT_FILENO);
(void)dup2(devnullfd, STDERR_FILENO);
if (devnullfd > 2)
{
close(devnullfd);
}
}
/* deny core dumps, since memory contains unencrypted private keys */
struct rlimit rlim;
rlim.rlim_cur = rlim.rlim_max = 0;
if (setrlimit(RLIMIT_CORE, &rlim) < 0)
{
fprintf(stderr, "setrlimit RLIMIT_CORE: %s", strerror(errno));
exit(1);
}
}
static void
handle_connection(int client_fd)
{
int rdp_fd = -1;
int rc;
void *channel = WTSVirtualChannelOpenEx(WTS_CURRENT_SESSION,
"SSHAGENT",
WTS_CHANNEL_OPTION_DYNAMIC_PRI_MED);
if (channel == NULL)
{
fprintf(stderr, "WTSVirtualChannelOpenEx() failed\n");
}
unsigned int retlen;
int *retdata;
rc = WTSVirtualChannelQuery(channel,
WTSVirtualFileHandle,
(void **)&retdata,
&retlen);
if (!rc)
{
fprintf(stderr, "WTSVirtualChannelQuery() failed\n");
}
if (retlen != sizeof(rdp_fd))
{
fprintf(stderr, "WTSVirtualChannelQuery() returned wrong length %u\n",
retlen);
}
rdp_fd = *retdata;
int client_going = 1;
while (client_going)
{
struct pollfd pollfd[2];
enum
{
RDP_FD = 0,
CLIENT_FD
};
/* Wait for data from RDP or the client */
pollfd[RDP_FD].fd = rdp_fd;
pollfd[RDP_FD].events = POLLIN;
pollfd[RDP_FD].revents = 0;
pollfd[CLIENT_FD].fd = client_fd;
pollfd[CLIENT_FD].events = POLLIN;
pollfd[CLIENT_FD].revents = 0;
poll(pollfd, 2, -1);
if ((pollfd[RDP_FD].revents & (POLLIN | POLLHUP)) != 0)
{
/* Read from RDP and write to the client */
char buffer[4096];
unsigned int bytes_to_write;
rc = WTSVirtualChannelRead(channel,
/* TimeOut = */ 5000,
buffer,
sizeof(buffer),
&bytes_to_write);
if (rc == 1)
{
char *pos = buffer;
errno = 0;
while (bytes_to_write > 0)
{
int bytes_written = send(client_fd, pos, bytes_to_write, 0);
if (bytes_written > 0)
{
bytes_to_write -= bytes_written;
pos += bytes_written;
}
else if (bytes_written == 0)
{
fprintf(stderr, "send() returned 0!\n");
}
else if (errno != EINTR)
{
/* Error */
fprintf(stderr, "Error %d on recv\n", errno);
client_going = 0;
}
}
}
else
{
/* Error */
fprintf(stderr, "WTSVirtualChannelRead() failed: %d\n", errno);
client_going = 0;
}
}
if ((pollfd[CLIENT_FD].revents & (POLLIN | POLLHUP)) != 0)
{
/* Read from the client and write to RDP */
char buffer[4096];
ssize_t bytes_to_write = recv(client_fd, buffer, sizeof(buffer), 0);
if (bytes_to_write > 0)
{
char *pos = buffer;
while (bytes_to_write > 0)
{
unsigned int bytes_written;
int rc = WTSVirtualChannelWrite(channel,
pos,
bytes_to_write,
&bytes_written);
if (rc == 0)
{
fprintf(stderr, "WTSVirtualChannelWrite() failed: %d\n",
errno);
client_going = 0;
}
else
{
bytes_to_write -= bytes_written;
pos += bytes_written;
}
}
}
else if (bytes_to_write == 0)
{
/* Client has closed connection */
client_going = 0;
}
else
{
/* Error */
fprintf(stderr, "Error %d on recv\n", errno);
client_going = 0;
}
}
}
WTSVirtualChannelClose(channel);
}
int
main(int argc, char **argv)
{
/* Setup the Unix domain socket and daemon process */
struct sockaddr_un addr;
setup_ssh_agent(&addr);
/* Wait for a client to connect to the socket */
while (is_going)
{
struct pollfd pollfd;
pollfd.fd = sa_uds_fd;
pollfd.events = POLLIN;
pollfd.revents = 0;
poll(pollfd, 1, -1);
/* If something connected then get it...
* (You can test this using "socat - UNIX-CONNECT:<udspath>".) */
if ((pollfd.revents & (POLLIN | POLLHUP)) != 0)
{
socklen_t addrsize = sizeof(addr);
int client_fd = accept(sa_uds_fd,
(struct sockaddr *)&addr,
&addrsize);
handle_connection(client_fd);
close(client_fd);
}
}
close(sa_uds_fd);
unlink(socket_name);
return 0;
}
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