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/*
* Copyright (C) 2014, 2015 Firejail Authors
*
* This file is part of firejail project
*
* 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 Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/
#include "firejail.h"
#include <sys/mount.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <fcntl.h>
static char *client_filter =
"*filter\n"
":INPUT DROP [0:0]\n"
":FORWARD DROP [0:0]\n"
":OUTPUT ACCEPT [0:0]\n"
"-A INPUT -i lo -j ACCEPT\n"
"# echo replay is handled by -m state RELEATED/ESTABLISHED below\n"
"#-A INPUT -p icmp --icmp-type echo-reply -j ACCEPT\n"
"-A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT\n"
"-A INPUT -p icmp --icmp-type destination-unreachable -j ACCEPT\n"
"-A INPUT -p icmp --icmp-type time-exceeded -j ACCEPT\n"
"-A INPUT -p icmp --icmp-type echo-request -j ACCEPT \n"
"COMMIT\n";
void check_netfilter_file(const char *fname) {
if (is_dir(fname) || is_link(fname) || strstr(fname, "..")) {
fprintf(stderr, "Error: invalid network filter file\n");
exit(1);
}
// access call checks as real UID/GID, not as effective UID/GID
if (access(fname, R_OK)) {
fprintf(stderr, "Error: cannot access network filter file\n");
exit(1);
}
}
void netfilter(const char *fname) {
// default filter
char *filter = client_filter;
// custom filter
int allocated = 0;
if (fname) {
// buffer the filter
struct stat s;
if (stat(fname, &s) == -1) {
fprintf(stderr, "Error: cannot find network filter file\n");
exit(1);
}
filter = malloc(s.st_size + 1); // + '\0'
if (!filter)
errExit("malloc");
memset(filter, 0, s.st_size + 1);
/* coverity[toctou] */
FILE *fp = fopen(fname, "r");
if (!fp) {
fprintf(stderr, "Error: cannot open network filter file\n");
exit(1);
}
size_t sz = fread(filter, 1, s.st_size, fp);
if ((off_t)sz != s.st_size) {
fprintf(stderr, "Error: cannot read network filter file\n");
exit(1);
}
fclose(fp);
allocated = 1;
}
// temporarily mount a tempfs on top of /tmp directory
if (mount("tmpfs", "/tmp", "tmpfs", MS_NOSUID | MS_STRICTATIME | MS_REC, "mode=755,gid=0") < 0)
errExit("mounting /tmp");
// create the filter file
FILE *fp = fopen("/tmp/netfilter", "w");
if (!fp) {
fprintf(stderr, "Error: cannot open /tmp/netfilter file\n");
exit(1);
}
fprintf(fp, "%s\n", filter);
fclose(fp);
// find iptables command
struct stat s;
char *iptables = NULL;
char *iptables_restore = NULL;
if (stat("/sbin/iptables", &s) == 0) {
iptables = "/sbin/iptables";
iptables_restore = "/sbin/iptables-restore";
}
else if (stat("/usr/sbin/iptables", &s) == 0) {
iptables = "/usr/sbin/iptables";
iptables_restore = "/usr/sbin/iptables-restore";
}
if (iptables == NULL || iptables_restore == NULL) {
fprintf(stderr, "Error: iptables command not found\n");
goto doexit;
}
// push filter
pid_t child = fork();
if (child < 0)
errExit("fork");
if (child == 0) {
if (arg_debug)
printf("Installing network filter:\n%s\n", filter);
int fd;
if((fd = open("/tmp/netfilter", O_RDONLY)) == -1) {
fprintf(stderr,"Error: cannot open /tmp/netfilter\n");
exit(1);
}
dup2(fd,STDIN_FILENO);
close(fd);
// wipe out environment variables
environ = NULL;
execl(iptables_restore, iptables_restore, NULL);
// it will never get here!!!
}
// wait for the child to finish
waitpid(child, NULL, 0);
// debug
if (arg_debug) {
child = fork();
if (child < 0)
errExit("fork");
if (child == 0) {
environ = NULL;
execl(iptables, iptables, "-vL", NULL);
// it will never get here!!!
}
// wait for the child to finish
waitpid(child, NULL, 0);
}
doexit:
// unmount /tmp
umount("/tmp");
if (allocated)
free(filter);
}
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