runfilter.cc

/** @file runfilter.cc
 * @brief Run an external filter and capture its output in a std::string.
 *
 * Copyright (C) 2003,2006,2007,2009,2010,2011,2013 Olly Betts
 *
 * 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 2 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, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
 */

#include <config.h>

#include "runfilter.h"

#include <iostream>
#include <string>

#include <sys/types.h>
#include "safeerrno.h"
#include "safefcntl.h"
#include <cstdio>
#ifdef HAVE_SYS_TIME_H
# include <sys/time.h>
#endif
#ifdef HAVE_SYS_RESOURCE_H
# include <sys/resource.h>
#endif
#include "safesysselect.h"
#ifdef HAVE_SYS_SOCKET_H
# include <sys/socket.h>
#endif
#include "safesyswait.h"
#include "safeunistd.h"

#if defined HAVE_FORK && defined HAVE_SOCKETPAIR
# include <signal.h>
#endif

#include "freemem.h"

#ifdef _MSC_VER
# define popen _popen
# define pclose _pclose
#endif

using namespace std;

#if defined HAVE_FORK && defined HAVE_SOCKETPAIR
static pid_t pid_to_kill_on_signal;

#ifdef HAVE_SIGACTION
static struct sigaction old_hup_handler;
static struct sigaction old_int_handler;
static struct sigaction old_quit_handler;
static struct sigaction old_term_handler;

extern "C" {

static void
handle_signal(int signum)
{
    if (pid_to_kill_on_signal) {
	kill(pid_to_kill_on_signal, SIGKILL);
	pid_to_kill_on_signal = 0;
    }
    switch (signum) {
	case SIGHUP:
	    sigaction(signum, &old_hup_handler, NULL);
	    break;
	case SIGINT:
	    sigaction(signum, &old_int_handler, NULL);
	    break;
	case SIGQUIT:
	    sigaction(signum, &old_quit_handler, NULL);
	    break;
	case SIGTERM:
	    sigaction(signum, &old_term_handler, NULL);
	    break;
	default:
	    return;
    }
    raise(signum);
}

}

void
runfilter_init()
{
    struct sigaction sa;
    sa.sa_handler = handle_signal;
    sigemptyset(&sa.sa_mask);
    sa.sa_flags = 0;

    sigaction(SIGHUP, &sa, &old_hup_handler);
    sigaction(SIGINT, &sa, &old_int_handler);
    sigaction(SIGQUIT, &sa, &old_quit_handler);
    sigaction(SIGTERM, &sa, &old_term_handler);
}
#else
static sighandler_t old_hup_handler;
static sighandler_t old_int_handler;
static sighandler_t old_quit_handler;
static sighandler_t old_term_handler;

extern "C" {

static void
handle_signal(int signum)
{
    if (pid_to_kill_on_signal) {
	kill(pid_to_kill_on_signal, SIGKILL);
	pid_to_kill_on_signal = 0;
    }
    switch (signum) {
	case SIGHUP:
	    signal(signum, old_hup_handler);
	    break;
	case SIGINT:
	    signal(signum, old_int_handler);
	    break;
	case SIGQUIT:
	    signal(signum, old_quit_handler);
	    break;
	case SIGTERM:
	    signal(signum, old_term_handler);
	    break;
	default:
	    return;
    }
    raise(signum);
}

}

void
runfilter_init()
{
    old_hup_handler = signal(SIGHUP, handle_signal);
    old_int_handler = signal(SIGINT, handle_signal);
    old_quit_handler = signal(SIGQUIT, handle_signal);
    old_term_handler = signal(SIGTERM, handle_signal);
}
#endif
#else
void
runfilter_init()
{
}
#endif

string
stdout_to_string(const string &cmd)
{
    string out;
#if defined HAVE_FORK && defined HAVE_SOCKETPAIR
    // We want to be able to get the exit status of the child process.
    signal(SIGCHLD, SIG_DFL);

    int fds[2];
    if (socketpair(AF_UNIX, SOCK_STREAM, PF_UNSPEC, fds) < 0)
	throw ReadError();

    pid_t child = fork();
    if (child == 0) {
	// We're the child process.

#ifdef HAVE_SETPGID
	// Put the child process into its own process group, so that we can
	// easily kill it and any children it in turn forks if we need to.
	setpgid(0, 0);
	pid_to_kill_on_signal = -child;
#else
	pid_to_kill_on_signal = child;
#endif

	// Close the parent's side of the socket pair.
	close(fds[0]);

	// Connect stdout to our side of the socket pair.
	dup2(fds[1], 1);

#ifdef HAVE_SETRLIMIT
	// Impose some pretty generous resource limits to prevent run-away
	// filter programs from causing problems.

	// Limit CPU time to 300 seconds (5 minutes).
	struct rlimit cpu_limit = { 300, RLIM_INFINITY } ;
	setrlimit(RLIMIT_CPU, &cpu_limit);

#if defined RLIMIT_AS || defined RLIMIT_VMEM || defined RLIMIT_DATA
	// Limit process data to free physical memory.
	long mem = get_free_physical_memory();
	if (mem > 0) {
	    struct rlimit ram_limit = {
		static_cast<rlim_t>(mem),
		RLIM_INFINITY
	    };
#ifdef RLIMIT_AS
	    setrlimit(RLIMIT_AS, &ram_limit);
#elif defined RLIMIT_VMEM
	    setrlimit(RLIMIT_VMEM, &ram_limit);
#else
	    // Only limits the data segment rather than the total address
	    // space, but that's better than nothing.
	    setrlimit(RLIMIT_DATA, &ram_limit);
#endif
	}
#endif
#endif

	execl("/bin/sh", "/bin/sh", "-c", cmd.c_str(), (void*)NULL);
	_exit(-1);
    }

    // We're the parent process.

    // Close the child's side of the socket pair.
    close(fds[1]);
    if (child == -1) {
	// fork() failed.
	close(fds[0]);
	throw ReadError();
    }

    int fd = fds[0];

    fd_set readfds;
    FD_ZERO(&readfds);
    while (true) {
	// If we wait 300 seconds (5 minutes) without getting data from the
	// filter, then give up to avoid waiting forever for a filter which
	// has ended up blocked waiting for something which will never happen.
	struct timeval tv;
	tv.tv_sec = 300;
	tv.tv_usec = 0;
	FD_SET(fd, &readfds);
	int r = select(fd + 1, &readfds, NULL, NULL, &tv);
	if (r <= 0) {
	    if (r < 0) {
		if (errno == EINTR) {
		    // select() interrupted by a signal, so retry.
		    continue;
		}
		cerr << "Reading from filter failed (" << strerror(errno) << ")"
		     << endl;
	    } else {
		cerr << "Filter inactive for too long" << endl;
	    }
#ifdef HAVE_SETPGID
	    kill(-child, SIGKILL);
#else
	    kill(child, SIGKILL);
#endif
	    close(fd);
	    int status = 0;
	    while (waitpid(child, &status, 0) < 0 && errno == EINTR) { }
	    pid_to_kill_on_signal = 0;
	    throw ReadError();
	}

	char buf[4096];
	ssize_t res = read(fd, buf, sizeof(buf));
	if (res == 0) break;
	if (res == -1) {
	    if (errno == EINTR) {
		// read() interrupted by a signal, so retry.
		continue;
	    }
	    close(fd);
#ifdef HAVE_SETPGID
	    kill(-child, SIGKILL);
#endif
	    int status = 0;
	    while (waitpid(child, &status, 0) < 0 && errno == EINTR) { }
	    pid_to_kill_on_signal = 0;
	    throw ReadError();
	}
	out.append(buf, res);
    }

    close(fd);
#ifdef HAVE_SETPGID
    kill(-child, SIGKILL);
#endif
    int status = 0;
    while (waitpid(child, &status, 0) < 0) {
	if (errno != EINTR)
	    throw ReadError();
    }
    pid_to_kill_on_signal = 0;
#else
    FILE * fh = popen(cmd.c_str(), "r");
    if (fh == NULL) throw ReadError();
    while (!feof(fh)) {
	char buf[4096];
	size_t len = fread(buf, 1, 4096, fh);
	if (ferror(fh)) {
	    (void)pclose(fh);
	    throw ReadError();
	}
	out.append(buf, len);
    }
    int status = pclose(fh);
#endif

    if (status != 0) {
	if (WIFEXITED(status) && WEXITSTATUS(status) == 127) {
	    throw NoSuchFilter();
	}
#ifdef SIGXCPU
	if (WIFSIGNALED(status) && WTERMSIG(status) == SIGXCPU) {
	    cerr << "Filter process consumed too much CPU time" << endl;
	}
#endif
	throw ReadError();
    }
    return out;
}