SSLproxy/privsep.c

/*
 * SSLsplit - transparent and scalable SSL/TLS interception
 * Copyright (c) 2009-2014, Daniel Roethlisberger <daniel@roe.ch>
 * All rights reserved.
 * http://www.roe.ch/SSLsplit
 *
 * 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 unmodified, 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.
 */

#include "privsep.h"

#include "sys.h"
#include "util.h"
#include "log.h"
#include "attrib.h"
#include "defaults.h"

#include <sys/types.h>
#include <sys/socket.h>
#include <sys/select.h>
#include <sys/wait.h>
#include <netinet/in.h>
#include <signal.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <libgen.h>
#include <fcntl.h>


/*
 * Privilege separation functionality.
 *
 * The server code has limitations on the internal functionality that can be
 * used, namely only those that are initialized before forking.
 */

/* maximal message sizes */
#define PRIVSEP_MAX_REQ_SIZE	512	/* arbitrary limit */
#define PRIVSEP_MAX_ANS_SIZE	(1+sizeof(int))
/* command byte */
#define PRIVSEP_REQ_CLOSE	0	/* closing command socket */
#define PRIVSEP_REQ_OPENFILE	1	/* open content log file */
#define PRIVSEP_REQ_OPENFILE_P	2	/* open content log file w/mkpath */
#define PRIVSEP_REQ_OPENSOCK	3	/* open socket and pass fd */
/* response byte */
#define PRIVSEP_ANS_SUCCESS	0	/* success */
#define PRIVSEP_ANS_UNK_CMD	1	/* unknown command */
#define PRIVSEP_ANS_INVALID	2	/* invalid message */
#define PRIVSEP_ANS_DENIED	3	/* request denied */
#define PRIVSEP_ANS_SYS_ERR	4	/* system error; arg=errno */

/* communication with signal handler */
static int received_sighup;
static int received_sigint;
static int received_sigquit;
static int received_sigchld;
static int received_sigusr1;
static int selfpipe_wrfd; /* write end of pipe used for unblocking select */

static void
privsep_server_signal_handler(int sig)
{
	int saved_errno;

	saved_errno = errno;
	switch (sig) {
	case SIGHUP:
		received_sighup = 1;
		break;
	case SIGINT:
		received_sigint = 1;
		break;
	case SIGQUIT:
		received_sigquit = 1;
		break;
	case SIGCHLD:
		received_sigchld = 1;
		break;
	case SIGUSR1:
		received_sigusr1 = 1;
		break;
	}
	if (selfpipe_wrfd != -1) {
		ssize_t n;

		do {
			n = write(selfpipe_wrfd, "!", 1);
		} while (n == -1 && errno == EINTR);
		if (n == -1) {
			log_err_printf("Failed to write from signal handler: "
			               "%s (%i)\n", strerror(errno), errno);
			/* ignore error */
		}
	}
	errno = saved_errno;
}

static int WUNRES
privsep_server_openfile_verify(opts_t *opts, char *fn, int mkpath)
{
	if (mkpath && !opts->contentlog_isspec)
		return -1;
	if (!mkpath && !opts->contentlog_isdir)
		return -1;
	if (strstr(fn, mkpath ? opts->contentlog_basedir
	                      : opts->contentlog) != fn ||
	    strstr(fn, "/../"))
		return -1;
	return 0;
}

static int WUNRES
privsep_server_openfile(char *fn, int mkpath)
{
	int fd;

	if (mkpath) {
		char *filedir, *fn2;

		fn2 = strdup(fn);
		if (!fn2) {
			log_err_printf("Could not duplicate filname: %s (%i)\n",
			               strerror(errno), errno);
			return -1;
		}
		filedir = dirname(fn2);
		if (!filedir) {
			log_err_printf("Could not get dirname: %s (%i)\n",
			               strerror(errno), errno);
			free(fn2);
			return -1;
		}
		if (sys_mkpath(filedir, DFLT_DIRMODE) == -1) {
			log_err_printf("Could not create directory '%s': %s (%i)\n",
			               filedir, strerror(errno), errno);
			free(fn2);
			return -1;
		}
		free(fn2);
	}

	fd = open(fn, O_WRONLY|O_APPEND|O_CREAT, DFLT_FILEMODE);
	if (fd == -1) {
		log_err_printf("Failed to open '%s': %s (%i)\n",
		               fn, strerror(errno), errno);
		return -1;
	}
	return fd;
}

static int WUNRES
privsep_server_opensock_verify(opts_t *opts, void *arg)
{
	for (proxyspec_t *spec = opts->spec; spec; spec = spec->next) {
		if (spec == arg)
			return 0;
	}
	return 1;
}

static int WUNRES
privsep_server_opensock(proxyspec_t *spec)
{
	evutil_socket_t fd;
	int on = 1;
	int rv;

	fd = socket(spec->listen_addr.ss_family, SOCK_STREAM, IPPROTO_TCP);
	if (fd == -1) {
		log_err_printf("Error from socket(): %s (%i)\n",
		               strerror(errno), errno);
		evutil_closesocket(fd);
		return -1;
	}

	rv = evutil_make_socket_nonblocking(fd);
	if (rv == -1) {
		log_err_printf("Error making socket nonblocking: %s (%i)\n",
		               strerror(errno), errno);
		evutil_closesocket(fd);
		return -1;
	}

	rv = setsockopt(fd, SOL_SOCKET, SO_KEEPALIVE, (void*)&on, sizeof(on));
	if (rv == -1) {
		log_err_printf("Error from setsockopt(SO_KEEPALIVE): %s (%i)\n",
		               strerror(errno), errno);
		evutil_closesocket(fd);
		return -1;
	}

	rv = evutil_make_listen_socket_reuseable(fd);
	if (rv == -1) {
		log_err_printf("Error from setsockopt(SO_REUSABLE): %s\n",
		               strerror(errno));
		evutil_closesocket(fd);
		return -1;
	}

	if (spec->natsocket && (spec->natsocket(fd) == -1)) {
		log_err_printf("Error from spec->natsocket()\n");
		evutil_closesocket(fd);
		return -1;
	}

	rv = bind(fd, (struct sockaddr *)&spec->listen_addr,
	          spec->listen_addrlen);
	if (rv == -1) {
		log_err_printf("Error from bind(): %s\n", strerror(errno));
		evutil_closesocket(fd);
		return -1;
	}

	return fd;
}

/*
 * Handle a single request on a readable server socket.
 * Returns 0 on success, 1 on EOF and -1 on error.
 */
static int WUNRES
privsep_server_handle_req(opts_t *opts, int srvsock)
{
	char req[PRIVSEP_MAX_REQ_SIZE];
	char ans[PRIVSEP_MAX_ANS_SIZE];
	ssize_t n;
	int mkpath = 0;

	if ((n = sys_recvmsgfd(srvsock, req, sizeof(req),
	                       NULL)) == -1) {
		if (errno == EPIPE || errno == ECONNRESET) {
			/* unfriendly EOF, leave server */
			return 1;
		}
		log_err_printf("Failed to receive msg: %s (%i)\n",
		               strerror(errno), errno);
		return -1;
	}
	if (n == 0) {
		/* EOF, leave server; will not happen for SOCK_DGRAM sockets */
		return 1;
	}
	log_dbg_printf("Received privsep req type %02x sz %zd on srvsock %i\n",
	               req[0], n, srvsock);
	switch (req[0]) {
	case PRIVSEP_REQ_CLOSE: {
		/* client indicates EOF through close message */
		return 1;
	}
	case PRIVSEP_REQ_OPENFILE_P:
		mkpath = 1;
	case PRIVSEP_REQ_OPENFILE: {
		char *fn;
		int fd;

		if (n < 2) {
			ans[0] = PRIVSEP_ANS_INVALID;
			if (sys_sendmsgfd(srvsock, ans, 1, -1) == -1) {
				log_err_printf("Sending message failed: %s (%i"
				               ")\n", strerror(errno), errno);
				return -1;
			}
		}
		if (!(fn = malloc(n))) {
			ans[0] = PRIVSEP_ANS_SYS_ERR;
			*((int*)&ans[1]) = errno;
			if (sys_sendmsgfd(srvsock, ans, 1 + sizeof(int),
			                  -1) == -1) {
				log_err_printf("Sending message failed: %s (%i"
				               ")\n", strerror(errno), errno);
				return -1;
			}
			return 0;
		}
		memcpy(fn, req + 1, n - 1);
		fn[n - 1] = '\0';
		if (privsep_server_openfile_verify(opts, fn, mkpath) == -1) {
			free(fn);
			ans[0] = PRIVSEP_ANS_DENIED;
			if (sys_sendmsgfd(srvsock, ans, 1, -1) == -1) {
				log_err_printf("Sending message failed: %s (%i"
				               ")\n", strerror(errno), errno);
				return -1;
			}
			return 0;
		}
		if ((fd = privsep_server_openfile(fn, mkpath)) == -1) {
			free(fn);
			ans[0] = PRIVSEP_ANS_SYS_ERR;
			*((int*)&ans[1]) = errno;
			if (sys_sendmsgfd(srvsock, ans, 1 + sizeof(int),
			                  -1) == -1) {
				log_err_printf("Sending message failed: %s (%i"
				               ")\n", strerror(errno), errno);
				return -1;
			}
			return 0;
		} else {
			free(fn);
			ans[0] = PRIVSEP_ANS_SUCCESS;
			if (sys_sendmsgfd(srvsock, ans, 1, fd) == -1) {
				close(fd);
				log_err_printf("Sending message failed: %s (%i"
				               ")\n", strerror(errno), errno);
				return -1;
			}
			close(fd);
			return 0;
		}
		/* not reached */
		break;
	}
	case PRIVSEP_REQ_OPENSOCK: {
		proxyspec_t *arg;
		int s;

		if (n != sizeof(char) + sizeof(arg)) {
			ans[0] = PRIVSEP_ANS_INVALID;
			if (sys_sendmsgfd(srvsock, ans, 1, -1) == -1) {
				log_err_printf("Sending message failed: %s (%i"
				               ")\n", strerror(errno), errno);
				return -1;
			}
			return 0;
		}
		arg = *(proxyspec_t**)(&req[1]);
		if (privsep_server_opensock_verify(opts, arg) == -1) {
			ans[0] = PRIVSEP_ANS_DENIED;
			if (sys_sendmsgfd(srvsock, ans, 1, -1) == -1) {
				log_err_printf("Sending message failed: %s (%i"
				               ")\n", strerror(errno), errno);
				return -1;
			}
			return 0;
		}
		if ((s = privsep_server_opensock(arg)) == -1) {
			ans[0] = PRIVSEP_ANS_SYS_ERR;
			*((int*)&ans[1]) = errno;
			if (sys_sendmsgfd(srvsock, ans, 1 + sizeof(int),
			                  -1) == -1) {
				log_err_printf("Sending message failed: %s (%i"
				               ")\n", strerror(errno), errno);
				return -1;
			}
			return 0;
		} else {
			ans[0] = PRIVSEP_ANS_SUCCESS;
			if (sys_sendmsgfd(srvsock, ans, 1, s) == -1) {
				evutil_closesocket(s);
				log_err_printf("Sending message failed: %s (%i"
				               ")\n", strerror(errno), errno);
				return -1;
			}
			evutil_closesocket(s);
			return 0;
		}
		/* not reached */
		break;
	}
	default:
		ans[0] = PRIVSEP_ANS_UNK_CMD;
		if (sys_sendmsgfd(srvsock, ans, 1, -1) == -1) {
			log_err_printf("Sending message failed: %s (%i"
			               ")\n", strerror(errno), errno);
			return -1;
		}
	}
	return 0;
}

/*
 * Privilege separation server (main privileged monitor loop)
 *
 * sigpipe is the self-pipe trick pipe used for communicating signals to
 * the main event loop and break out of select() without race conditions.
 * srvsock[] is a dynamic array of connected privsep server sockets to serve.
 * Caller is responsible for freeing memory after returning, if necessary.
 * childpid is the pid of the child process to forward signals to.
 *
 * Returns 0 on a successful clean exit and -1 on errors.
 */
static int
privsep_server(opts_t *opts, int sigpipe, int srvsock[], size_t nsrvsock,
               pid_t childpid)
{
	int srveof[nsrvsock];
	size_t i = 0;

	for (i = 0; i < nsrvsock; i++) {
		srveof[i] = 0;
	}

	for (;;) {
		fd_set readfds;
		int maxfd, rv;

		do {
			FD_ZERO(&readfds);
			FD_SET(sigpipe, &readfds);
			maxfd = sigpipe;
			for (i = 0; i < nsrvsock; i++) {
				if (!srveof[i]) {
					FD_SET(srvsock[i], &readfds);
					maxfd = util_max(maxfd, srvsock[i]);
				}
			}
			rv = select(maxfd + 1, &readfds, NULL, NULL, NULL);
		} while (rv == -1 && errno == EINTR);
		if (rv == -1) {
			log_err_printf("Select failed: %s (%i)\n",
			               strerror(errno), errno);
			return -1;
		}

		if (FD_ISSET(sigpipe, &readfds)) {
			char buf[16];
			/* first drain the signal pipe, then deal with
			 * all the individual signal flags */
			read(sigpipe, buf, sizeof(buf));
			if (received_sigquit) {
				kill(childpid, SIGQUIT);
				received_sigquit = 0;
			}
			if (received_sighup) {
				kill(childpid, SIGHUP);
				received_sighup = 0;
			}
			if (received_sigusr1) {
				kill(childpid, SIGUSR1);
				received_sigusr1 = 0;
			}
			if (received_sigint) {
				/* if we don't detach from the TTY, the
				 * child process receives SIGINT directly */
				if (opts->detach)
					kill(childpid, SIGINT);
				received_sigint = 0;
			}
			if (received_sigchld) {
				/* break the loop; because we are using
				 * SOCKET_DGRAM we don't get EOF conditions
				 * on the disconnected socket ends here
				 * unless we attempt to write or read, so
				 * we depend on SIGCHLD to notify us of
				 * our child erroring out or crashing */
				break;
			}
		}

		for (i = 0; i < nsrvsock; i++) {
			if (FD_ISSET(srvsock[i], &readfds)) {
				int rv = privsep_server_handle_req(opts,
				                                   srvsock[i]);
				if (rv == -1) {
					log_err_printf("Failed to handle "
					               "privsep req "
					               "on srvsock %i\n",
					               srvsock[i]);
					return -1;
				}
				if (rv == 1)
					srveof[i] = 1;
			}
		}

		/* break if all server sockets received an EOF */
		i = 0;
		while (i < nsrvsock && srveof[i])
			i++;
		if (i == nsrvsock)
			break;
	}

	return 0;
}

int
privsep_client_openfile(int clisock, const char *fn, int mkpath)
{
	char ans[PRIVSEP_MAX_ANS_SIZE];
	char req[1 + strlen(fn)];
	int fd = -1;
	ssize_t n;

	req[0] = mkpath ? PRIVSEP_REQ_OPENFILE_P : PRIVSEP_REQ_OPENFILE;
	memcpy(req + 1, fn, sizeof(req) - 1);

	if (sys_sendmsgfd(clisock, req, sizeof(req), -1) == -1) {
		return -1;
	}

	if ((n = sys_recvmsgfd(clisock, ans, sizeof(ans), &fd)) == -1) {
		return -1;
	}

	if (n < 1) {
		errno = EINVAL;
		return -1;
	}

	switch (ans[0]) {
	case PRIVSEP_ANS_SUCCESS:
		break;
	case PRIVSEP_ANS_DENIED:
		errno = EACCES;
		return -1;
	case PRIVSEP_ANS_SYS_ERR:
		if (n < (ssize_t)(1 + sizeof(int))) {
			errno = EINVAL;
			return -1;
		}
		errno = *((int*)&ans[1]);
		return -1;
	case PRIVSEP_ANS_UNK_CMD:
	case PRIVSEP_ANS_INVALID:
	default:
		return -1;
	}

	return fd;
}

int
privsep_client_opensock(int clisock, const proxyspec_t *spec)
{
	char ans[PRIVSEP_MAX_ANS_SIZE];
	char req[1 + sizeof(spec)];
	int fd = -1;
	ssize_t n;

	req[0] = PRIVSEP_REQ_OPENSOCK;
	*((const proxyspec_t **)&req[1]) = spec;

	if (sys_sendmsgfd(clisock, req, sizeof(req), -1) == -1) {
		return -1;
	}

	if ((n = sys_recvmsgfd(clisock, ans, sizeof(ans), &fd)) == -1) {
		return -1;
	}

	if (n < 1) {
		errno = EINVAL;
		return -1;
	}

	switch (ans[0]) {
	case PRIVSEP_ANS_SUCCESS:
		break;
	case PRIVSEP_ANS_DENIED:
		errno = EACCES;
		return -1;
	case PRIVSEP_ANS_SYS_ERR:
		if (n < (ssize_t)(1 + sizeof(int))) {
			errno = EINVAL;
			return -1;
		}
		errno = *((int*)&ans[1]);
		return -1;
	case PRIVSEP_ANS_UNK_CMD:
	case PRIVSEP_ANS_INVALID:
	default:
		return -1;
	}

	return fd;
}

int
privsep_client_close(int clisock)
{
	char req[1];

	req[0] = PRIVSEP_REQ_CLOSE;

	if (sys_sendmsgfd(clisock, req, sizeof(req), -1) == -1) {
		close(clisock);
		return -1;
	}

	close(clisock);
	return 0;
}

/*
 * Fork and set up privilege separated monitor process.
 * Returns -1 on error before forking, 1 as parent, or 0 as child.
 * The array of clisock's will get filled with nclisock privsep client
 * sockets only for the child; on error and in the parent process it
 * will not be touched.
 */
int
privsep_fork(opts_t *opts, int clisock[], size_t nclisock)
{
	int selfpipev[2]; /* self-pipe trick: signal handler -> select */
	int chldpipev[2]; /* el cheapo interprocess sync early after fork */
	int sockcliv[nclisock][2];
	pid_t pid;

	received_sigquit = 0;
	received_sighup = 0;
	received_sigint = 0;
	received_sigchld = 0;
	received_sigusr1 = 0;

	if (pipe(selfpipev) == -1) {
		log_err_printf("Failed to create self-pipe: %s (%i)\n",
		               strerror(errno), errno);
		return -1;
	}
	log_dbg_printf("Created self-pipe [r=%i,w=%i]\n",
	               selfpipev[0], selfpipev[1]);

	if (pipe(chldpipev) == -1) {
		log_err_printf("Failed to create chld-pipe: %s (%i)\n",
		               strerror(errno), errno);
		return -1;
	}
	log_dbg_printf("Created chld-pipe [r=%i,w=%i]\n",
	               chldpipev[0], chldpipev[1]);

	for (size_t i = 0; i < nclisock; i++) {
		if (socketpair(AF_UNIX, SOCK_DGRAM, 0, sockcliv[i]) == -1) {
			log_err_printf("Failed to create socket pair %zu: "
			               "%s (%i)\n", i, strerror(errno), errno);
			return -1;
		}
		log_dbg_printf("Created socketpair %zu [p=%i,c=%i]\n",
		               i, sockcliv[i][0], sockcliv[i][1]);
	}

	pid = fork();
	if (pid == -1) {
		log_err_printf("Failed to fork: %s (%i)\n",
		               strerror(errno), errno);
		close(selfpipev[0]);
		close(selfpipev[1]);
		close(chldpipev[0]);
		close(chldpipev[1]);
		for (size_t i = 0; i < nclisock; i++) {
			close(sockcliv[i][0]);
			close(sockcliv[i][1]);
		}
		return -1;
	} else if (pid == 0) {
		/* child */
		close(selfpipev[0]);
		close(selfpipev[1]);
		for (size_t i = 0; i < nclisock; i++)
			close(sockcliv[i][0]);
		/* wait until parent has installed signal handlers,
		 * intentionally ignoring errors */
		char buf[1];
		ssize_t n;
		close(chldpipev[1]);
		do {
			n = read(chldpipev[0], buf, sizeof(buf));
		} while (n == -1 && errno == EINTR);
		close(chldpipev[0]);

		/* return the privsep client sockets */
		for (size_t i = 0; i < nclisock; i++)
			clisock[i] = sockcliv[i][1];
		return 0;
	}
	/* parent */
	for (size_t i = 0; i < nclisock; i++)
		close(sockcliv[i][1]);
	selfpipe_wrfd = selfpipev[1];

	/* close file descriptors opened by preinit's only needed in client;
	 * we still call the preinit's before forking in order to provide
	 * better user feedback and less privsep complexity */
	nat_preinit_undo();
	log_preinit_undo();

	/* If the child exits before the parent installs the signal handler
	 * here, we have a race condition; this is solved by the client
	 * blocking on the reading end of a pipe (chldpipev[0]). */
	if (signal(SIGHUP, privsep_server_signal_handler) == SIG_ERR) {
		log_err_printf("Failed to install SIGHUP handler: %s (%i)\n",
		               strerror(errno), errno);
		return -1;
	}
	if (signal(SIGINT, privsep_server_signal_handler) == SIG_ERR) {
		log_err_printf("Failed to install SIGINT handler: %s (%i)\n",
		               strerror(errno), errno);
		return -1;
	}
	if (signal(SIGQUIT, privsep_server_signal_handler) == SIG_ERR) {
		log_err_printf("Failed to install SIGQUIT handler: %s (%i)\n",
		               strerror(errno), errno);
		return -1;
	}
	if (signal(SIGUSR1, privsep_server_signal_handler) == SIG_ERR) {
		log_err_printf("Failed to install SIGUSR1 handler: %s (%i)\n",
		               strerror(errno), errno);
		return -1;
	}
	if (signal(SIGCHLD, privsep_server_signal_handler) == SIG_ERR) {
		log_err_printf("Failed to install SIGCHLD handler: %s (%i)\n",
		               strerror(errno), errno);
		return -1;
	}

	/* unblock the child */
	close(chldpipev[0]);
	close(chldpipev[1]);

	int socksrv[nclisock];
	for (size_t i = 0; i < nclisock; i++)
		socksrv[i] = sockcliv[i][0];
	if (privsep_server(opts, selfpipev[0], socksrv, nclisock, pid) == -1) {
		log_err_printf("Privsep server failed: %s (%i)\n",
		               strerror(errno), errno);
		/* fall through */
	}

	for (size_t i = 0; i < nclisock; i++)
		close(sockcliv[i][0]);
	selfpipe_wrfd = -1; /* tell signal handler not to write anymore */
	close(selfpipev[0]);
	close(selfpipev[1]);

	int status;
	wait(&status);
	if (WIFEXITED(status)) {
		if (WEXITSTATUS(status) != 0) {
			log_err_printf("Child proc %lld exited with status %d\n",
			               (long long)pid, WEXITSTATUS(status));
		} else {
			log_dbg_printf("Child proc %lld exited with status %d\n",
			               (long long)pid, WEXITSTATUS(status));
		}
	} else if (WIFSIGNALED(status)) {
		log_err_printf("Child proc %lld killed by signal %d\n",
		               (long long)pid, WTERMSIG(status));
	} else {
		log_err_printf("Child proc %lld neither exited nor killed\n",
		               (long long)pid);
	}

	return 1;
}

/* vim: set noet ft=c: */