svr-agentfwd.c - third_party/dropbear - Git at Google

 /*
  * Dropbear - a SSH2 server
  *
  * Copyright (c) 2002,2003 Matt Johnston
  * All rights reserved.
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
  * in the Software without restriction, including without limitation the rights
  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  * copies of the Software, and to permit persons to whom the Software is
  * furnished to do so, subject to the following conditions:
  *
  * The above copyright notice and this permission notice shall be included in
  * all copies or substantial portions of the Software.
  *
  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  * SOFTWARE. */

 /* This file (agentfwd.c) handles authentication agent forwarding, for OpenSSH
  * style agents. */

 #include "includes.h"

 #ifndef DISABLE_AGENTFWD

 #include "agentfwd.h"
 #include "session.h"
 #include "ssh.h"
 #include "dbutil.h"
 #include "chansession.h"
 #include "channel.h"
 #include "packet.h"
 #include "buffer.h"
 #include "random.h"
 #include "listener.h"

 #define AGENTDIRPREFIX "/tmp/dropbear-"

 static int send_msg_channel_open_agent(int fd);
 static int bindagent(int fd, struct ChanSess * chansess);
 static void agentaccept(struct Listener * listener, int sock);

 /* Handles client requests to start agent forwarding, sets up listening socket.
  * Returns DROPBEAR_SUCCESS or DROPBEAR_FAILURE */
 int agentreq(struct ChanSess * chansess) {

 	int fd;

 	if (chansess->agentlistener != NULL) {
 		return DROPBEAR_FAILURE;
 	}

 	/* create listening socket */
 	fd = socket(PF_UNIX, SOCK_STREAM, 0);
 	if (fd < 0) {
 		goto fail;
 	}

 	/* create the unix socket dir and file */
 	if (bindagent(fd, chansess) == DROPBEAR_FAILURE) {
 		goto fail;
 	}

 	/* listen */
 	if (listen(fd, 20) < 0) {
 		goto fail;
 	}

 	/* set non-blocking */
 	if (fcntl(fd, F_SETFL, O_NONBLOCK) < 0) {
 		goto fail;
 	}

 	/* pass if off to listener */
 	chansess->agentlistener = new_listener( &fd, 1, 0, chansess,
 								agentaccept, NULL);

 	if (chansess->agentlistener == NULL) {
 		goto fail;
 	}

 	return DROPBEAR_SUCCESS;

 fail:
 	/* cleanup */
 	agentcleanup(chansess);

 	return DROPBEAR_FAILURE;
 }

 /* accepts a connection on the forwarded socket and opens a new channel for it
  * back to the client */
 /* returns DROPBEAR_SUCCESS or DROPBEAR_FAILURE */
 static void agentaccept(struct Listener * listener, int sock) {

 	int fd;

 	fd = accept(sock, NULL, NULL);
 	if (fd < 0) {
 		TRACE(("accept failed"));
 		return;
 	}

 	if (send_msg_channel_open_agent(fd) != DROPBEAR_SUCCESS) {
 		close(fd);
 	}

 }

 /* set up the environment variable pointing to the socket. This is called
  * just before command/shell execution, after dropping priveleges */
 void agentset(struct ChanSess * chansess) {

 	char *path = NULL;
 	int len;

 	if (chansess->agentlistener == NULL) {
 		return;
 	}

 	/* 2 for "/" and "\0" */
 	len = strlen(chansess->agentdir) + strlen(chansess->agentfile) + 2;

 	path = m_malloc(len);
 	snprintf(path, len, "%s/%s", chansess->agentdir, chansess->agentfile);
 	addnewvar("SSH_AUTH_SOCK", path);
 	m_free(path);
 }

 /* close the socket, remove the socket-file */
 void agentcleanup(struct ChanSess * chansess) {

 	char *path = NULL;
 	uid_t uid;
 	gid_t gid;
 	int len;

 	if (chansess->agentlistener != NULL) {
 		remove_listener(chansess->agentlistener);
 		chansess->agentlistener = NULL;
 	}

 	if (chansess->agentfile != NULL && chansess->agentdir != NULL) {

 		/* Remove the dir as the user. That way they can't cause problems except
 		 * for themselves */
 		uid = getuid();
 		gid = getgid();
 		if ((setegid(ses.authstate.pw->pw_gid)) < 0 ||
 			(seteuid(ses.authstate.pw->pw_uid)) < 0) {
 			dropbear_exit("failed to set euid");
 		}

 		/* 2 for "/" and "\0" */
 		len = strlen(chansess->agentdir) + strlen(chansess->agentfile) + 2;

 		path = m_malloc(len);
 		snprintf(path, len, "%s/%s", chansess->agentdir, chansess->agentfile);
 		unlink(path);
 		m_free(path);

 		rmdir(chansess->agentdir);

 		if ((seteuid(uid)) < 0 ||
 			(setegid(gid)) < 0) {
 			dropbear_exit("failed to revert euid");
 		}

 		m_free(chansess->agentfile);
 		m_free(chansess->agentdir);
 	}

 }

 static const struct ChanType chan_agent = {
 	0, /* sepfds */
 	"auth-agent@openssh.com",
 	NULL,
 	NULL,
 	NULL,
 	NULL
 };


 /* helper for accepting an agent request */
 static int send_msg_channel_open_agent(int fd) {

 	if (send_msg_channel_open_init(fd, &chan_agent) == DROPBEAR_SUCCESS) {
 		encrypt_packet();
 		return DROPBEAR_SUCCESS;
 	} else {
 		return DROPBEAR_FAILURE;
 	}
 }

 /* helper for creating the agent socket-file
    returns DROPBEAR_SUCCESS or DROPBEAR_FAILURE */
 static int bindagent(int fd, struct ChanSess * chansess) {

 	struct sockaddr_un addr;
 	unsigned int prefix;
 	char path[sizeof(addr.sun_path)], sockfile[sizeof(addr.sun_path)];
 	mode_t mode;
 	int i;
 	uid_t uid;
 	gid_t gid;
 	int ret = DROPBEAR_FAILURE;

 	/* drop to user privs to make the dir/file */
 	uid = getuid();
 	gid = getgid();
 	if ((setegid(ses.authstate.pw->pw_gid)) < 0 ||
 		(seteuid(ses.authstate.pw->pw_uid)) < 0) {
 		dropbear_exit("failed to set euid");
 	}

 	memset((void*)&addr, 0x0, sizeof(addr));
 	addr.sun_family = AF_UNIX;

 	mode = S_IRWXU;

 	for (i = 0; i < 20; i++) {
 		genrandom((unsigned char*)&prefix, sizeof(prefix));
 		/* we want 32 bits (8 hex digits) - "/tmp/dropbear-f19c62c0" */
 		snprintf(path, sizeof(path), AGENTDIRPREFIX "%.8x", prefix);

 		if (mkdir(path, mode) == 0) {
 			goto bindsocket;
 		}
 		if (errno != EEXIST) {
 			break;
 		}
 	}
 	/* couldn't make a dir */
 	goto out;

 bindsocket:
 	/* Format is "/tmp/dropbear-0246dead/auth-d00f7654-23".
 	 * The "23" is the file desc, the random data is to avoid collisions
 	 * between subsequent user processes reusing socket fds (odds are now
 	 * 1/(2^64) */
 	genrandom((unsigned char*)&prefix, sizeof(prefix));
 	snprintf(sockfile, sizeof(sockfile), "auth-%.8x-%d", prefix, fd);

 	snprintf(addr.sun_path, sizeof(addr.sun_path), "%s/%s", path, sockfile);

 	if (bind(fd, (struct sockaddr*)&addr, sizeof(addr)) == 0) {
 		chansess->agentdir = m_strdup(path);
 		chansess->agentfile = m_strdup(sockfile);
 		ret = DROPBEAR_SUCCESS;
 	}


 out:
 	if ((seteuid(uid)) < 0 ||
 		(setegid(gid)) < 0) {
 		dropbear_exit("failed to revert euid");
 	}
 	return ret;
 }

 #endif
	/*
	* Dropbear - a SSH2 server
	*
	* Copyright (c) 2002,2003 Matt Johnston
	* All rights reserved.
	*
	* Permission is hereby granted, free of charge, to any person obtaining a copy
	* of this software and associated documentation files (the "Software"), to deal
	* in the Software without restriction, including without limitation the rights
	* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
	* copies of the Software, and to permit persons to whom the Software is
	* furnished to do so, subject to the following conditions:
	*
	* The above copyright notice and this permission notice shall be included in
	* all copies or substantial portions of the Software.
	*
	* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
	* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
	* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
	* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
	* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
	* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
	* SOFTWARE. */

	/* This file (agentfwd.c) handles authentication agent forwarding, for OpenSSH
	* style agents. */

	#include "includes.h"

	#ifndef DISABLE_AGENTFWD

	#include "agentfwd.h"
	#include "session.h"
	#include "ssh.h"
	#include "dbutil.h"
	#include "chansession.h"
	#include "channel.h"
	#include "packet.h"
	#include "buffer.h"
	#include "random.h"
	#include "listener.h"

	#define AGENTDIRPREFIX "/tmp/dropbear-"

	static int send_msg_channel_open_agent(int fd);
	static int bindagent(int fd, struct ChanSess * chansess);
	static void agentaccept(struct Listener * listener, int sock);

	/* Handles client requests to start agent forwarding, sets up listening socket.
	* Returns DROPBEAR_SUCCESS or DROPBEAR_FAILURE */
	int agentreq(struct ChanSess * chansess) {

	int fd;

	if (chansess->agentlistener != NULL) {
	return DROPBEAR_FAILURE;
	}

	/* create listening socket */
	fd = socket(PF_UNIX, SOCK_STREAM, 0);
	if (fd < 0) {
	goto fail;
	}

	/* create the unix socket dir and file */
	if (bindagent(fd, chansess) == DROPBEAR_FAILURE) {
	goto fail;
	}

	/* listen */
	if (listen(fd, 20) < 0) {
	goto fail;
	}

	/* set non-blocking */
	if (fcntl(fd, F_SETFL, O_NONBLOCK) < 0) {
	goto fail;
	}

	/* pass if off to listener */
	chansess->agentlistener = new_listener( &fd, 1, 0, chansess,
	agentaccept, NULL);

	if (chansess->agentlistener == NULL) {
	goto fail;
	}

	return DROPBEAR_SUCCESS;

	fail:
	/* cleanup */
	agentcleanup(chansess);

	return DROPBEAR_FAILURE;
	}

	/* accepts a connection on the forwarded socket and opens a new channel for it
	* back to the client */
	/* returns DROPBEAR_SUCCESS or DROPBEAR_FAILURE */
	static void agentaccept(struct Listener * listener, int sock) {

	int fd;

	fd = accept(sock, NULL, NULL);
	if (fd < 0) {
	TRACE(("accept failed"));
	return;
	}

	if (send_msg_channel_open_agent(fd) != DROPBEAR_SUCCESS) {
	close(fd);
	}

	}

	/* set up the environment variable pointing to the socket. This is called
	* just before command/shell execution, after dropping priveleges */
	void agentset(struct ChanSess * chansess) {

	char *path = NULL;
	int len;

	if (chansess->agentlistener == NULL) {
	return;
	}

	/* 2 for "/" and "\0" */
	len = strlen(chansess->agentdir) + strlen(chansess->agentfile) + 2;

	path = m_malloc(len);
	snprintf(path, len, "%s/%s", chansess->agentdir, chansess->agentfile);
	addnewvar("SSH_AUTH_SOCK", path);
	m_free(path);
	}

	/* close the socket, remove the socket-file */
	void agentcleanup(struct ChanSess * chansess) {

	char *path = NULL;
	uid_t uid;
	gid_t gid;
	int len;

	if (chansess->agentlistener != NULL) {
	remove_listener(chansess->agentlistener);
	chansess->agentlistener = NULL;
	}

	if (chansess->agentfile != NULL && chansess->agentdir != NULL) {

	/* Remove the dir as the user. That way they can't cause problems except
	* for themselves */
	uid = getuid();
	gid = getgid();
	if ((setegid(ses.authstate.pw->pw_gid)) < 0 \|\|
	(seteuid(ses.authstate.pw->pw_uid)) < 0) {
	dropbear_exit("failed to set euid");
	}

	/* 2 for "/" and "\0" */
	len = strlen(chansess->agentdir) + strlen(chansess->agentfile) + 2;

	path = m_malloc(len);
	snprintf(path, len, "%s/%s", chansess->agentdir, chansess->agentfile);
	unlink(path);
	m_free(path);

	rmdir(chansess->agentdir);

	if ((seteuid(uid)) < 0 \|\|
	(setegid(gid)) < 0) {
	dropbear_exit("failed to revert euid");
	}

	m_free(chansess->agentfile);
	m_free(chansess->agentdir);
	}

	}

	static const struct ChanType chan_agent = {
	0, /* sepfds */
	"auth-agent@openssh.com",
	NULL,
	NULL,
	NULL,
	NULL
	};


	/* helper for accepting an agent request */
	static int send_msg_channel_open_agent(int fd) {

	if (send_msg_channel_open_init(fd, &chan_agent) == DROPBEAR_SUCCESS) {
	encrypt_packet();
	return DROPBEAR_SUCCESS;
	} else {
	return DROPBEAR_FAILURE;
	}
	}

	/* helper for creating the agent socket-file
	returns DROPBEAR_SUCCESS or DROPBEAR_FAILURE */
	static int bindagent(int fd, struct ChanSess * chansess) {

	struct sockaddr_un addr;
	unsigned int prefix;
	char path[sizeof(addr.sun_path)], sockfile[sizeof(addr.sun_path)];
	mode_t mode;
	int i;
	uid_t uid;
	gid_t gid;
	int ret = DROPBEAR_FAILURE;

	/* drop to user privs to make the dir/file */
	uid = getuid();
	gid = getgid();
	if ((setegid(ses.authstate.pw->pw_gid)) < 0 \|\|
	(seteuid(ses.authstate.pw->pw_uid)) < 0) {
	dropbear_exit("failed to set euid");
	}

	memset((void*)&addr, 0x0, sizeof(addr));
	addr.sun_family = AF_UNIX;

	mode = S_IRWXU;

	for (i = 0; i < 20; i++) {
	genrandom((unsigned char*)&prefix, sizeof(prefix));
	/* we want 32 bits (8 hex digits) - "/tmp/dropbear-f19c62c0" */
	snprintf(path, sizeof(path), AGENTDIRPREFIX "%.8x", prefix);

	if (mkdir(path, mode) == 0) {
	goto bindsocket;
	}
	if (errno != EEXIST) {
	break;
	}
	}
	/* couldn't make a dir */
	goto out;

	bindsocket:
	/* Format is "/tmp/dropbear-0246dead/auth-d00f7654-23".
	* The "23" is the file desc, the random data is to avoid collisions
	* between subsequent user processes reusing socket fds (odds are now
	* 1/(2^64) */
	genrandom((unsigned char*)&prefix, sizeof(prefix));
	snprintf(sockfile, sizeof(sockfile), "auth-%.8x-%d", prefix, fd);

	snprintf(addr.sun_path, sizeof(addr.sun_path), "%s/%s", path, sockfile);

	if (bind(fd, (struct sockaddr*)&addr, sizeof(addr)) == 0) {
	chansess->agentdir = m_strdup(path);
	chansess->agentfile = m_strdup(sockfile);
	ret = DROPBEAR_SUCCESS;
	}


	out:
	if ((seteuid(uid)) < 0 \|\|
	(setegid(gid)) < 0) {
	dropbear_exit("failed to revert euid");
	}
	return ret;
	}

	#endif