view svr-main.c @ 1866:adfcdfb161a4

Fix missing NULL terminator for re-exec Also fixes fallback, sockets were not kept open
author Matt Johnston <matt@ucc.asn.au>
date Mon, 31 Jan 2022 11:12:58 +0800
parents 2b3a8026a6ce
children 0dcc5b0d93fa
line wrap: on
line source
/*
 * Dropbear - a SSH2 server
 * 
 * Copyright (c) 2002-2006 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. */

#include "includes.h"
#include "dbutil.h"
#include "session.h"
#include "buffer.h"
#include "signkey.h"
#include "runopts.h"
#include "dbrandom.h"
#include "crypto_desc.h"

static size_t listensockets(int *sock, size_t sockcount, int *maxfd);
static void sigchld_handler(int dummy);
static void sigsegv_handler(int);
static void sigintterm_handler(int fish);
static void main_inetd(void);
static void main_noinetd(int argc, char ** argv);
static void commonsetup(void);

#if defined(DBMULTI_dropbear) || !DROPBEAR_MULTI
#if defined(DBMULTI_dropbear) && DROPBEAR_MULTI
int dropbear_main(int argc, char ** argv)
#else
int main(int argc, char ** argv)
#endif
{
	_dropbear_exit = svr_dropbear_exit;
	_dropbear_log = svr_dropbear_log;

	disallow_core();

	if (argc < 1) {
		dropbear_exit("Bad argc");
	}

	/* get commandline options */
	svr_getopts(argc, argv);

#if INETD_MODE
	/* service program mode */
	if (svr_opts.inetdmode) {
		main_inetd();
		/* notreached */
	}
#endif

#if DROPBEAR_DO_REEXEC
	if (svr_opts.reexec_child) {
#ifdef PR_SET_NAME
		/* Fix the "Name:" in /proc/pid/status, otherwise it's
		a FD number from fexecve.
		Failure doesn't really matter, it's mostly aesthetic */
		prctl(PR_SET_NAME, basename(argv[0]), 0, 0);
#endif
		main_inetd();
		/* notreached */
	}
#endif

#if NON_INETD_MODE
	main_noinetd(argc, argv);
	/* notreached */
#endif

	dropbear_exit("Compiled without normal mode, can't run without -i\n");
	return -1;
}
#endif

#if INETD_MODE || DROPBEAR_DO_REEXEC
static void main_inetd() {
	char *host, *port = NULL;

	/* Set up handlers, syslog */
	commonsetup();

	seedrandom();

	if (!svr_opts.reexec_child) {
		/* In case our inetd was lax in logging source addresses */
		get_socket_address(0, NULL, NULL, &host, &port, 0);
			dropbear_log(LOG_INFO, "Child connection from %s:%s", host, port);
		m_free(host);
		m_free(port);

		/* Don't check the return value - it may just fail since inetd has
		 * already done setsid() after forking (xinetd on Darwin appears to do
		 * this */
		setsid();
	}

	/* Start service program 
	 * -1 is a dummy childpipe, just something we can close() without 
	 * mattering. */
	svr_session(0, -1);

	/* notreached */
}
#endif /* INETD_MODE */

#if NON_INETD_MODE
static void main_noinetd(int argc, char ** argv) {
	fd_set fds;
	unsigned int i, j;
	int val;
	int maxsock = -1;
	int listensocks[MAX_LISTEN_ADDR];
	size_t listensockcount = 0;
	FILE *pidfile = NULL;
	int execfd = -1;

	int childpipes[MAX_UNAUTH_CLIENTS];
	char * preauth_addrs[MAX_UNAUTH_CLIENTS];

	int childsock;
	int childpipe[2];

	(void)argc;
	(void)argv;

	/* Note: commonsetup() must happen before we daemon()ise. Otherwise
	   daemon() will chdir("/"), and we won't be able to find local-dir
	   hostkeys. */
	commonsetup();

	/* sockets to identify pre-authenticated clients */
	for (i = 0; i < MAX_UNAUTH_CLIENTS; i++) {
		childpipes[i] = -1;
	}
	memset(preauth_addrs, 0x0, sizeof(preauth_addrs));

	/* Set up the listening sockets */
	listensockcount = listensockets(listensocks, MAX_LISTEN_ADDR, &maxsock);
	if (listensockcount == 0)
	{
		dropbear_exit("No listening ports available.");
	}

	for (i = 0; i < listensockcount; i++) {
		FD_SET(listensocks[i], &fds);
	}

#if DROPBEAR_DO_REEXEC
	execfd = open(argv[0], O_CLOEXEC|O_RDONLY);
	if (execfd < 0) {
		/* Just fallback to straight fork */
		TRACE(("Couldn't open own binary %s, disabling re-exec: %s", argv[0], strerror(errno)))
	}
#endif

	/* fork */
	if (svr_opts.forkbg) {
		int closefds = 0;
#if !DEBUG_TRACE
		if (!opts.usingsyslog) {
			closefds = 1;
		}
#endif
		if (daemon(0, closefds) < 0) {
			dropbear_exit("Failed to daemonize: %s", strerror(errno));
		}
	}

	/* should be done after syslog is working */
	if (svr_opts.forkbg) {
		dropbear_log(LOG_INFO, "Running in background");
	} else {
		dropbear_log(LOG_INFO, "Not backgrounding");
	}

	/* create a PID file so that we can be killed easily */
	pidfile = fopen(svr_opts.pidfile, "w");
	if (pidfile) {
		fprintf(pidfile, "%d\n", getpid());
		fclose(pidfile);
	}

	/* incoming connection select loop */
	for(;;) {

		DROPBEAR_FD_ZERO(&fds);

		/* listening sockets */
		for (i = 0; i < listensockcount; i++) {
			FD_SET(listensocks[i], &fds);
		}

		/* pre-authentication clients */
		for (i = 0; i < MAX_UNAUTH_CLIENTS; i++) {
			if (childpipes[i] >= 0) {
				FD_SET(childpipes[i], &fds);
				maxsock = MAX(maxsock, childpipes[i]);
			}
		}

		val = select(maxsock+1, &fds, NULL, NULL, NULL);

		if (ses.exitflag) {
			unlink(svr_opts.pidfile);
			dropbear_exit("Terminated by signal");
		}

		if (val == 0) {
			/* timeout reached - shouldn't happen. eh */
			continue;
		}

		if (val < 0) {
			if (errno == EINTR) {
				continue;
			}
			dropbear_exit("Listening socket error");
		}

		/* close fds which have been authed or closed - svr-auth.c handles
		 * closing the auth sockets on success */
		for (i = 0; i < MAX_UNAUTH_CLIENTS; i++) {
			if (childpipes[i] >= 0 && FD_ISSET(childpipes[i], &fds)) {
				m_close(childpipes[i]);
				childpipes[i] = -1;
				m_free(preauth_addrs[i]);
			}
		}

		/* handle each socket which has something to say */
		for (i = 0; i < listensockcount; i++) {
			size_t num_unauthed_for_addr = 0;
			size_t num_unauthed_total = 0;
			char *remote_host = NULL, *remote_port = NULL;
			pid_t fork_ret = 0;
			size_t conn_idx = 0;
			struct sockaddr_storage remoteaddr;
			socklen_t remoteaddrlen;

			if (!FD_ISSET(listensocks[i], &fds)) 
				continue;

			remoteaddrlen = sizeof(remoteaddr);
			childsock = accept(listensocks[i], 
					(struct sockaddr*)&remoteaddr, &remoteaddrlen);

			if (childsock < 0) {
				/* accept failed */
				continue;
			}

			/* Limit the number of unauthenticated connections per IP */
			getaddrstring(&remoteaddr, &remote_host, NULL, 0);

			num_unauthed_for_addr = 0;
			num_unauthed_total = 0;
			for (j = 0; j < MAX_UNAUTH_CLIENTS; j++) {
				if (childpipes[j] >= 0) {
					num_unauthed_total++;
					if (strcmp(remote_host, preauth_addrs[j]) == 0) {
						num_unauthed_for_addr++;
					}
				} else {
					/* a free slot */
					conn_idx = j;
				}
			}

			if (num_unauthed_total >= MAX_UNAUTH_CLIENTS
					|| num_unauthed_for_addr >= MAX_UNAUTH_PER_IP) {
				goto out;
			}

			seedrandom();

			if (pipe(childpipe) < 0) {
				TRACE(("error creating child pipe"))
				goto out;
			}

#if DEBUG_NOFORK
			fork_ret = 0;
#else
			fork_ret = fork();
#endif
			if (fork_ret < 0) {
				dropbear_log(LOG_WARNING, "Error forking: %s", strerror(errno));
				goto out;
			}

			addrandom((void*)&fork_ret, sizeof(fork_ret));

			if (fork_ret > 0) {

				/* parent */
				childpipes[conn_idx] = childpipe[0];
				m_close(childpipe[1]);
				preauth_addrs[conn_idx] = remote_host;
				remote_host = NULL;

			} else {

				/* child */
				getaddrstring(&remoteaddr, NULL, &remote_port, 0);
				dropbear_log(LOG_INFO, "Child connection from %s:%s", remote_host, remote_port);
				m_free(remote_host);
				m_free(remote_port);

#ifndef DEBUG_NOFORK
				if (setsid() < 0) {
					dropbear_exit("setsid: %s", strerror(errno));
				}
#endif

				/* make sure we close sockets */
				for (j = 0; j < listensockcount; j++) {
					m_close(listensocks[j]);
				}

				m_close(childpipe[0]);

				if (execfd >= 0) {
#if DROPBEAR_DO_REEXEC
					/* Add "-2" to the args and re-execute ourself */
					char **new_argv = m_malloc(sizeof(char*) * (argc+2));
					memcpy(new_argv, argv, sizeof(char*) * argc);
					new_argv[argc] = "-2";
					new_argv[argc+1] = NULL;

					if ((dup2(childsock, STDIN_FILENO) < 0)) {
						dropbear_exit("dup2 failed: %s", strerror(errno));
					}
					if (fcntl(childsock, F_SETFD, FD_CLOEXEC) < 0) {
						TRACE(("cloexec for childsock %d failed: %s", childsock, strerror(errno)))
					}
					/* Re-execute ourself */
					fexecve(execfd, new_argv, environ);
					/* Not reached on success */

					/* Fall back on plain fork otherwise.
					 * To be removed in future once re-exec has been well tested */
					dropbear_log(LOG_WARNING, "fexecve failed, disabling re-exec: %s", strerror(errno));
					m_close(STDIN_FILENO);
					m_free(new_argv);
#endif /* DROPBEAR_DO_REEXEC */
				}

				/* start the session */
				svr_session(childsock, childpipe[1]);
				/* don't return */
				dropbear_assert(0);
			}

out:
			/* This section is important for the parent too */
			m_close(childsock);
			if (remote_host) {
				m_free(remote_host);
			}
		}
	} /* for(;;) loop */

	/* don't reach here */
}
#endif /* NON_INETD_MODE */


/* catch + reap zombie children */
static void sigchld_handler(int UNUSED(unused)) {
	struct sigaction sa_chld;

	const int saved_errno = errno;

	while(waitpid(-1, NULL, WNOHANG) > 0) {}

	sa_chld.sa_handler = sigchld_handler;
	sa_chld.sa_flags = SA_NOCLDSTOP;
	sigemptyset(&sa_chld.sa_mask);
	if (sigaction(SIGCHLD, &sa_chld, NULL) < 0) {
		dropbear_exit("signal() error");
	}
	errno = saved_errno;
}

/* catch any segvs */
static void sigsegv_handler(int UNUSED(unused)) {
	fprintf(stderr, "Aiee, segfault! You should probably report "
			"this as a bug to the developer\n");
	_exit(EXIT_FAILURE);
}

/* catch ctrl-c or sigterm */
static void sigintterm_handler(int UNUSED(unused)) {

	ses.exitflag = 1;
}

/* Things used by inetd and non-inetd modes */
static void commonsetup() {

	struct sigaction sa_chld;
#ifndef DISABLE_SYSLOG
	if (opts.usingsyslog) {
		startsyslog(PROGNAME);
	}
#endif

	/* set up cleanup handler */
	if (signal(SIGINT, sigintterm_handler) == SIG_ERR || 
#ifndef DEBUG_VALGRIND
		signal(SIGTERM, sigintterm_handler) == SIG_ERR ||
#endif
		signal(SIGPIPE, SIG_IGN) == SIG_ERR) {
		dropbear_exit("signal() error");
	}

	/* catch and reap zombie children */
	sa_chld.sa_handler = sigchld_handler;
	sa_chld.sa_flags = SA_NOCLDSTOP;
	sigemptyset(&sa_chld.sa_mask);
	if (sigaction(SIGCHLD, &sa_chld, NULL) < 0) {
		dropbear_exit("signal() error");
	}
	if (signal(SIGSEGV, sigsegv_handler) == SIG_ERR) {
		dropbear_exit("signal() error");
	}

	crypto_init();

	/* Now we can setup the hostkeys - needs to be after logging is on,
	 * otherwise we might end up blatting error messages to the socket */
	load_all_hostkeys();
}

/* Set up listening sockets for all the requested ports */
static size_t listensockets(int *socks, size_t sockcount, int *maxfd) {

	unsigned int i, n;
	char* errstring = NULL;
	size_t sockpos = 0;
	int nsock;

	TRACE(("listensockets: %d to try", svr_opts.portcount))

	for (i = 0; i < svr_opts.portcount; i++) {

		TRACE(("listening on '%s:%s'", svr_opts.addresses[i], svr_opts.ports[i]))

		nsock = dropbear_listen(svr_opts.addresses[i], svr_opts.ports[i], &socks[sockpos], 
				sockcount - sockpos,
				&errstring, maxfd);

		if (nsock < 0) {
			dropbear_log(LOG_WARNING, "Failed listening on '%s': %s", 
							svr_opts.ports[i], errstring);
			m_free(errstring);
			continue;
		}

		for (n = 0; n < (unsigned int)nsock; n++) {
			int sock = socks[sockpos + n];
			set_sock_priority(sock, DROPBEAR_PRIO_LOWDELAY);
#if DROPBEAR_SERVER_TCP_FAST_OPEN
			set_listen_fast_open(sock);
#endif
		}

		sockpos += nsock;

	}
	return sockpos;
}