pipe.c

/*
 * Routines used to setup various kinds of inter-process pipes.
 *
 * Copyright (C) 1996-2000 Andrew Tridgell
 * Copyright (C) 1996 Paul Mackerras
 * Copyright (C) 2001, 2002 Martin Pool <mbp@samba.org>
 * Copyright (C) 2004-2020 Wayne Davison
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, visit the http://fsf.org website.
 */

#include "rsync.h"

extern int am_sender;
extern int am_server;
extern int blocking_io;
extern int filesfrom_fd;
extern int munge_symlinks;
extern char *logfile_name;
extern int remote_option_cnt;
extern const char **remote_options;
extern struct chmod_mode_struct *chmod_modes;

/**
 * Create a child connected to us via its stdin/stdout.
 *
 * This is derived from CVS code
 *
 * Note that in the child STDIN is set to blocking and STDOUT
 * is set to non-blocking. This is necessary as rsh relies on stdin being blocking
 *  and ssh relies on stdout being non-blocking
 *
 * If blocking_io is set then use blocking io on both fds. That can be
 * used to cope with badly broken rsh implementations like the one on
 * Solaris.
 **/
pid_t piped_child(char **command, int *f_in, int *f_out)
{
	pid_t pid;
	int to_child_pipe[2];
	int from_child_pipe[2];

	if (DEBUG_GTE(CMD, 1))
		print_child_argv("opening connection using:", command);

	if (fd_pair(to_child_pipe) < 0 || fd_pair(from_child_pipe) < 0) {
		rsyserr(FERROR, errno, "pipe");
		exit_cleanup(RERR_IPC);
	}

	pid = do_fork();
	if (pid == -1) {
		rsyserr(FERROR, errno, "fork");
		exit_cleanup(RERR_IPC);
	}

	if (pid == 0) {
		if (dup2(to_child_pipe[0], STDIN_FILENO) < 0
		 || close(to_child_pipe[1]) < 0
		 || close(from_child_pipe[0]) < 0
		 || dup2(from_child_pipe[1], STDOUT_FILENO) < 0) {
			rsyserr(FERROR, errno, "Failed to dup/close");
			exit_cleanup(RERR_IPC);
		}
		if (to_child_pipe[0] != STDIN_FILENO)
			close(to_child_pipe[0]);
		if (from_child_pipe[1] != STDOUT_FILENO)
			close(from_child_pipe[1]);
		set_blocking(STDIN_FILENO);
		if (blocking_io > 0)
			set_blocking(STDOUT_FILENO);
		execvp(command[0], command);
		rsyserr(FERROR, errno, "Failed to exec %s", command[0]);
		exit_cleanup(RERR_IPC);
	}

	if (close(from_child_pipe[1]) < 0 || close(to_child_pipe[0]) < 0) {
		rsyserr(FERROR, errno, "Failed to close");
		exit_cleanup(RERR_IPC);
	}

	*f_in = from_child_pipe[0];
	*f_out = to_child_pipe[1];

	return pid;
}

/* This function forks a child which calls child_main().  First,
 * however, it has to establish communication paths to and from the
 * newborn child.  It creates two socket pairs -- one for writing to
 * the child (from the parent) and one for reading from the child
 * (writing to the parent).  Since that's four socket ends, each
 * process has to close the two ends it doesn't need.  The remaining
 * two socket ends are retained for reading and writing.  In the
 * child, the STDIN and STDOUT file descriptors refer to these
 * sockets.  In the parent, the function arguments f_in and f_out are
 * set to refer to these sockets. */
pid_t local_child(int argc, char **argv, int *f_in, int *f_out,
		  int (*child_main)(int, char*[]))
{
	pid_t pid;
	int to_child_pipe[2];
	int from_child_pipe[2];

	/* The parent process is always the sender for a local rsync. */
	assert(am_sender);

	if (fd_pair(to_child_pipe) < 0 || fd_pair(from_child_pipe) < 0) {
		rsyserr(FERROR, errno, "pipe");
		exit_cleanup(RERR_IPC);
	}

	pid = do_fork();
	if (pid == -1) {
		rsyserr(FERROR, errno, "fork");
		exit_cleanup(RERR_IPC);
	}

	if (pid == 0) {
		am_sender = 0;
		am_server = 1;
		filesfrom_fd = -1;
		munge_symlinks = 0; /* Each side needs its own option. */
		chmod_modes = NULL; /* Let the sending side handle this. */

		/* Let the client side handle this. */
		if (logfile_name) {
			logfile_name = NULL;
			logfile_close();
		}

		if (remote_option_cnt) {
			int rc = remote_option_cnt + 1;
			const char **rv = remote_options;
			if (!parse_arguments(&rc, &rv)) {
				option_error();
				exit_cleanup(RERR_SYNTAX);
			}
		}

		if (dup2(to_child_pipe[0], STDIN_FILENO) < 0
		 || close(to_child_pipe[1]) < 0
		 || close(from_child_pipe[0]) < 0
		 || dup2(from_child_pipe[1], STDOUT_FILENO) < 0) {
			rsyserr(FERROR, errno, "Failed to dup/close");
			exit_cleanup(RERR_IPC);
		}
		if (to_child_pipe[0] != STDIN_FILENO)
			close(to_child_pipe[0]);
		if (from_child_pipe[1] != STDOUT_FILENO)
			close(from_child_pipe[1]);
#ifdef ICONV_CONST
		setup_iconv();
#endif
		child_main(argc, argv);
	}

	if (close(from_child_pipe[1]) < 0 || close(to_child_pipe[0]) < 0) {
		rsyserr(FERROR, errno, "Failed to close");
		exit_cleanup(RERR_IPC);
	}

	*f_in = from_child_pipe[0];
	*f_out = to_child_pipe[1];

	return pid;
}