2 This file is part of GNUnet.
3 Copyright (C) 2010, 2011, 2012 Christian Grothoff
5 GNUnet is free software: you can redistribute it and/or modify it
6 under the terms of the GNU Affero General Public License as published
7 by the Free Software Foundation, either version 3 of the License,
8 or (at your option) any later version.
10 GNUnet is distributed in the hope that it will be useful, but
11 WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Affero General Public License for more details.
15 You should have received a copy of the GNU Affero General Public License
16 along with this program. If not, see <http://www.gnu.org/licenses/>.
18 SPDX-License-Identifier: AGPL3.0-or-later
22 * @file dns/gnunet-helper-dns.c
23 * @brief helper to install firewall rules to hijack all DNS traffic
24 * and send it to our virtual interface (except for DNS traffic
25 * that originates on the specified port). We then
26 * allow interacting with our virtual interface via stdin/stdout.
27 * @author Philipp Tölke
28 * @author Christian Grothoff
30 * This program alters the Linux firewall rules so that DNS traffic
31 * that ordinarily exits the system can be intercepted and managed by
32 * a virtual interface. In order to achieve this, DNS traffic is
33 * marked with the DNS_MARK given in below and re-routed to a custom
34 * table with the DNS_TABLE ID given below. Systems and
35 * administrators must take care to not cause conflicts with these
36 * values (it was deemed safest to hardcode them as passing these
37 * values as arguments might permit messing with arbitrary firewall
38 * rules, which would be dangerous). Traffic coming from the same
39 * group ID as the effective group ID that this process is running
40 * as is not intercepted.
42 * The code first sets up the virtual interface, then begins to
43 * redirect the DNS traffic to it, and then on errors or SIGTERM shuts
44 * down the virtual interface and removes the rules for the traffic
48 * Note that having this binary SUID is only partially safe: it will
49 * allow redirecting (and intercepting / mangling) of all DNS traffic
50 * originating from this system by any user who is able to run it.
51 * Furthermore, this code will make it trivial to DoS all DNS traffic
52 * originating from the current system, simply by sending it to
53 * nowhere (redirect stdout to /dev/null).
55 * Naturally, neither of these problems can be helped as this is the
56 * fundamental purpose of the binary. Certifying that this code is
57 * "safe" thus only means that it doesn't allow anything else (such
58 * as local priv. escalation, etc.).
60 * The following list of people have reviewed this code and considered
61 * it safe (within specifications) since the last modification (if you
62 * reviewed it, please have your name added to the list):
64 * - Christian Grothoff
73 * Need 'struct GNUNET_MessageHeader'.
75 #include "gnunet_crypto_lib.h"
76 #include "gnunet_common.h"
79 * Need DNS message types.
81 #include "gnunet_protocols.h"
84 * Maximum size of a GNUnet message (GNUNET_MAX_MESSAGE_SIZE)
86 #define MAX_SIZE 65536
88 #if ! HAVE_DECL_STRUCT_IN6_IFREQ
90 * This is in linux/include/net/ipv6.h, but not always exported...
94 struct in6_addr ifr6_addr;
95 uint32_t ifr6_prefixlen;
96 unsigned int ifr6_ifindex;
101 * Name and full path of IPTABLES binary.
103 static const char *sbin_iptables;
106 * Name and full path of IPTABLES binary.
108 static const char *sbin_ip6tables;
111 * Name and full path of sysctl binary
113 static const char *sbin_sysctl;
116 * Name and full path of IPTABLES binary.
118 static const char *sbin_ip;
121 * Port for DNS traffic.
123 #define DNS_PORT "53"
126 * Marker we set for our hijacked DNS traffic. We use GNUnet's
127 * port (2086) plus the DNS port (53) in HEX to make a 32-bit mark
128 * (which is hopefully long enough to not collide); so
129 * 0x08260035 = 136708149 (hopefully unique enough...).
131 #define DNS_MARK "136708149"
134 * Table we use for our DNS rules. 0-255 is the range and
135 * 0, 253, 254 and 255 are already reserved. As this is about
136 * DNS and as "53" is likely (fingers crossed!) high enough to
137 * not usually conflict with a normal user's setup, we use 53
138 * to give a hint that this has something to do with DNS.
140 #define DNS_TABLE "53"
144 * Control pipe for shutdown via signal. [0] is the read end,
145 * [1] is the write end.
151 * Signal handler called to initiate "nice" shutdown. Signals select
152 * loop via non-bocking pipe 'cpipe'.
154 * @param signal signal number of the signal (not used)
157 signal_handler (int signal)
159 /* ignore return value, as the signal handler could theoretically
160 be called many times before the shutdown can actually happen */
161 (void) write (cpipe[1], "K", 1);
166 * Open '/dev/null' and make the result the given
169 * @param target_fd desired FD to point to /dev/null
170 * @param flags open flags (O_RDONLY, O_WRONLY)
173 open_dev_null (int target_fd,
178 fd = open ("/dev/null", flags);
183 if (-1 == dup2 (fd, target_fd))
193 * Run the given command and wait for it to complete.
195 * @param file name of the binary to run
196 * @param cmd command line arguments (as given to 'execv')
197 * @return 0 on success, 1 on any error
200 fork_and_exec (const char *file,
217 /* we are the child process */
218 /* close stdin/stdout to not cause interference
219 with the helper's main protocol! */
221 open_dev_null (0, O_RDONLY);
223 open_dev_null (1, O_WRONLY);
224 (void) execv (file, cmd);
225 /* can only get here on error */
227 "exec `%s' failed: %s\n",
232 /* keep running waitpid as long as the only error we get is 'EINTR' */
233 while ((-1 == (ret = waitpid (pid, &status, 0))) &&
239 "waitpid failed: %s\n",
243 if (! (WIFEXITED (status) && (0 == WEXITSTATUS (status))))
245 /* child process completed and returned success, we're happy */
251 * Creates a tun-interface called @a dev;
253 * @param dev is asumed to point to a char[IFNAMSIZ]
254 * if *dev == '\\0', uses the name supplied by the kernel;
255 * @return the fd to the tun or -1 on error
269 if (-1 == (fd = open ("/dev/net/tun", O_RDWR)))
271 fprintf (stderr, "Error opening `%s': %s\n", "/dev/net/tun",
276 if (fd >= FD_SETSIZE)
278 fprintf (stderr, "File descriptor to large: %d", fd);
283 memset (&ifr, 0, sizeof(ifr));
284 ifr.ifr_flags = IFF_TUN;
287 strncpy (ifr.ifr_name, dev, IFNAMSIZ);
289 if (-1 == ioctl (fd, TUNSETIFF, (void *) &ifr))
291 fprintf (stderr, "Error with ioctl on `%s': %s\n", "/dev/net/tun",
296 strcpy (dev, ifr.ifr_name);
302 * @brief Sets the IPv6-Address given in @a address on the interface @a dev
304 * @param dev the interface to configure
305 * @param address the IPv6-Address
306 * @param prefix_len the length of the network-prefix
309 set_address6 (const char *dev, const char *address, unsigned long prefix_len)
312 struct in6_ifreq ifr6;
313 struct sockaddr_in6 sa6;
317 * parse the new address
319 memset (&sa6, 0, sizeof(struct sockaddr_in6));
320 sa6.sin6_family = AF_INET6;
321 if (1 != inet_pton (AF_INET6, address, sa6.sin6_addr.s6_addr))
324 "Failed to parse IPv6 address `%s': %s\n",
330 if (-1 == (fd = socket (PF_INET6, SOCK_DGRAM, 0)))
333 "Error creating IPv6 socket: %s (ignored)\n",
335 /* ignore error, maybe only IPv4 works on this system! */
339 memset (&ifr, 0, sizeof(struct ifreq));
341 * Get the index of the if
343 strncpy (ifr.ifr_name, dev, IFNAMSIZ);
344 if (-1 == ioctl (fd, SIOGIFINDEX, &ifr))
346 fprintf (stderr, "ioctl failed at %d: %s\n", __LINE__, strerror (errno));
351 memset (&ifr6, 0, sizeof(struct in6_ifreq));
352 ifr6.ifr6_addr = sa6.sin6_addr;
353 ifr6.ifr6_ifindex = ifr.ifr_ifindex;
354 ifr6.ifr6_prefixlen = prefix_len;
359 if (-1 == ioctl (fd, SIOCSIFADDR, &ifr6))
361 fprintf (stderr, "ioctl failed at line %d: %s\n", __LINE__,
370 if (-1 == ioctl (fd, SIOCGIFFLAGS, &ifr))
372 fprintf (stderr, "ioctl failed at line %d: %s\n", __LINE__,
379 * Add the UP and RUNNING flags
381 ifr.ifr_flags |= IFF_UP | IFF_RUNNING;
382 if (-1 == ioctl (fd, SIOCSIFFLAGS, &ifr))
384 fprintf (stderr, "ioctl failed at line %d: %s\n", __LINE__,
392 fprintf (stderr, "close failed: %s\n", strerror (errno));
399 * @brief Sets the IPv4-Address given in @a address on the interface @a dev
401 * @param dev the interface to configure
402 * @param address the IPv4-Address
403 * @param mask the netmask
406 set_address4 (const char *dev, const char *address, const char *mask)
409 struct sockaddr_in *addr;
412 memset (&ifr, 0, sizeof(struct ifreq));
413 addr = (struct sockaddr_in *) &(ifr.ifr_addr);
414 addr->sin_family = AF_INET;
419 if (1 != inet_pton (AF_INET, address, &addr->sin_addr.s_addr))
422 "Failed to parse IPv4 address `%s': %s\n",
428 if (-1 == (fd = socket (PF_INET, SOCK_DGRAM, 0)))
431 "Error creating IPv4 socket: %s\n",
436 strncpy (ifr.ifr_name, dev, IFNAMSIZ);
441 if (-1 == ioctl (fd, SIOCSIFADDR, &ifr))
443 fprintf (stderr, "ioctl failed at %d: %s\n", __LINE__, strerror (errno));
451 addr = (struct sockaddr_in *) &(ifr.ifr_netmask);
452 if (1 != inet_pton (AF_INET, mask, &addr->sin_addr.s_addr))
454 fprintf (stderr, "Failed to parse address `%s': %s\n", mask,
463 if (-1 == ioctl (fd, SIOCSIFNETMASK, &ifr))
465 fprintf (stderr, "ioctl failed at line %d: %s\n", __LINE__,
474 if (-1 == ioctl (fd, SIOCGIFFLAGS, &ifr))
476 fprintf (stderr, "ioctl failed at line %d: %s\n", __LINE__,
483 * Add the UP and RUNNING flags
485 ifr.ifr_flags |= IFF_UP | IFF_RUNNING;
486 if (-1 == ioctl (fd, SIOCSIFFLAGS, &ifr))
488 fprintf (stderr, "ioctl failed at line %d: %s\n", __LINE__,
496 fprintf (stderr, "close failed: %s\n", strerror (errno));
504 * Start forwarding to and from the tunnel. This function runs with
505 * "reduced" privileges (saved UID is still 0, but effective UID is
508 * @param fd_tun tunnel FD
514 * The buffer filled by reading from fd_tun
516 unsigned char buftun[MAX_SIZE];
517 ssize_t buftun_size = 0;
518 unsigned char *buftun_read = NULL;
521 * The buffer filled by reading from stdin
523 unsigned char bufin[MAX_SIZE];
524 ssize_t bufin_size = 0;
525 size_t bufin_rpos = 0;
526 unsigned char *bufin_read = NULL;
537 * We are supposed to read and the buffer is empty
538 * -> select on read from tun
540 if (0 == buftun_size)
541 FD_SET (fd_tun, &fds_r);
544 * We are supposed to read and the buffer is not empty
545 * -> select on write to stdout
551 * We are supposed to write and the buffer is empty
552 * -> select on read from stdin
554 if (NULL == bufin_read)
558 * We are supposed to write and the buffer is not empty
559 * -> select on write to tun
561 if (NULL != bufin_read)
562 FD_SET (fd_tun, &fds_w);
564 FD_SET (cpipe[0], &fds_r);
565 max = (fd_tun > cpipe[0]) ? fd_tun : cpipe[0];
567 int r = select (max + 1, &fds_r, &fds_w, NULL, NULL);
573 fprintf (stderr, "select failed: %s\n", strerror (errno));
579 if (FD_ISSET (cpipe[0], &fds_r))
580 return; /* aborted by signal */
582 if (FD_ISSET (fd_tun, &fds_r))
585 read (fd_tun, buftun + sizeof(struct GNUNET_MessageHeader),
586 MAX_SIZE - sizeof(struct GNUNET_MessageHeader));
587 if (-1 == buftun_size)
589 if ((errno == EINTR) ||
595 fprintf (stderr, "read-error: %s\n", strerror (errno));
598 if (0 == buftun_size)
600 fprintf (stderr, "EOF on tun\n");
603 buftun_read = buftun;
605 struct GNUNET_MessageHeader *hdr =
606 (struct GNUNET_MessageHeader *) buftun;
607 buftun_size += sizeof(struct GNUNET_MessageHeader);
608 hdr->type = htons (GNUNET_MESSAGE_TYPE_DNS_HELPER);
609 hdr->size = htons (buftun_size);
612 else if (FD_ISSET (1, &fds_w))
614 ssize_t written = write (1, buftun_read, buftun_size);
618 if ((errno == EINTR) ||
621 fprintf (stderr, "write-error to stdout: %s\n", strerror (errno));
626 fprintf (stderr, "write returned 0\n");
629 buftun_size -= written;
630 buftun_read += written;
633 if (FD_ISSET (0, &fds_r))
635 bufin_size = read (0, bufin + bufin_rpos, MAX_SIZE - bufin_rpos);
636 if (-1 == bufin_size)
639 if ((errno == EINTR) ||
642 fprintf (stderr, "read-error: %s\n", strerror (errno));
648 fprintf (stderr, "EOF on stdin\n");
652 struct GNUNET_MessageHeader *hdr;
655 bufin_rpos += bufin_size;
656 if (bufin_rpos < sizeof(struct GNUNET_MessageHeader))
658 hdr = (struct GNUNET_MessageHeader *) bufin;
659 if (ntohs (hdr->type) != GNUNET_MESSAGE_TYPE_DNS_HELPER)
661 fprintf (stderr, "protocol violation!\n");
664 if (ntohs (hdr->size) > bufin_rpos)
666 bufin_read = bufin + sizeof(struct GNUNET_MessageHeader);
667 bufin_size = ntohs (hdr->size) - sizeof(struct GNUNET_MessageHeader);
668 bufin_rpos -= bufin_size + sizeof(struct GNUNET_MessageHeader);
671 else if (FD_ISSET (fd_tun, &fds_w))
673 ssize_t written = write (fd_tun, bufin_read, bufin_size);
677 if ((errno == EINTR) ||
680 fprintf (stderr, "write-error to tun: %s\n", strerror (errno));
685 fprintf (stderr, "write returned 0\n");
689 bufin_size -= written;
690 bufin_read += written;
693 memmove (bufin, bufin_read, bufin_rpos);
694 bufin_read = NULL; /* start reading again */
706 * Main function of "gnunet-helper-dns", which opens a VPN tunnel interface,
707 * redirects all outgoing DNS traffic (except from the specified port) to that
708 * interface and then passes traffic from and to the interface via stdin/stdout.
710 * Once stdin/stdout close or have other errors, the tunnel is closed and the
711 * DNS traffic redirection is stopped.
713 * @param argc number of arguments
714 * @param argv 0: binary name (should be "gnunet-helper-vpn")
715 * 1: tunnel interface name (typically "gnunet-dns")
716 * 2: IPv6 address for the tunnel ("FE80::1")
717 * 3: IPv6 netmask length in bits ("64")
718 * 4: IPv4 address for the tunnel ("1.2.3.4")
719 * 5: IPv4 netmask ("255.255.0.0")
720 * 6: skip sysctl, routing and iptables setup ("0")
721 * @return 0 on success, otherwise code indicating type of error:
722 * 1 wrong number of arguments
723 * 2 invalid arguments (i.e. port number / prefix length wrong)
724 * 3 iptables not executable
725 * 4 ip not executable
726 * 5 failed to initialize tunnel interface
727 * 6 failed to initialize control pipe
728 * 8 failed to change routing table, cleanup successful
729 * 9-23 failed to change routing table and failed to undo some changes to routing table
730 * 24 failed to drop privs
731 * 25-39 failed to drop privs and then failed to undo some changes to routing table
732 * 40 failed to regain privs
733 * 41-55 failed to regain prisv and then failed to undo some changes to routing table
734 * 254 insufficient privileges
735 * 255 failed to handle kill signal properly
738 main (int argc, char *const*argv)
749 fprintf (stderr, "Fatal: must supply 6 arguments!\n");
753 /* assert privs so we can modify the firewall rules! */
755 #ifdef HAVE_SETRESUID
756 if (0 != setresuid (uid, 0, 0))
758 fprintf (stderr, "Failed to setresuid to root: %s\n", strerror (errno));
762 if (0 != seteuid (0))
764 fprintf (stderr, "Failed to seteuid back to root: %s\n", strerror (errno));
768 if (0 == strncmp (argv[6], "1", 2))
773 /* verify that the binaries we care about are executable */
775 if (0 == access (IPTABLES, X_OK))
776 sbin_iptables = IPTABLES;
779 if (0 == access ("/sbin/iptables", X_OK))
780 sbin_iptables = "/sbin/iptables";
781 else if (0 == access ("/usr/sbin/iptables", X_OK))
782 sbin_iptables = "/usr/sbin/iptables";
786 "Fatal: executable iptables not found in approved directories: %s\n",
791 if (0 == access (IP6TABLES, X_OK))
792 sbin_ip6tables = IP6TABLES;
795 if (0 == access ("/sbin/ip6tables", X_OK))
796 sbin_ip6tables = "/sbin/ip6tables";
797 else if (0 == access ("/usr/sbin/ip6tables", X_OK))
798 sbin_ip6tables = "/usr/sbin/ip6tables";
802 "Fatal: executable ip6tables not found in approved directories: %s\n",
807 if (0 == access (PATH_TO_IP, X_OK))
808 sbin_ip = PATH_TO_IP;
811 if (0 == access ("/sbin/ip", X_OK))
812 sbin_ip = "/sbin/ip";
813 else if (0 == access ("/usr/sbin/ip", X_OK))
814 sbin_ip = "/usr/sbin/ip";
815 else if (0 == access ("/bin/ip", X_OK)) /* gentoo has it there */
820 "Fatal: executable ip not found in approved directories: %s\n",
825 if (0 == access (SYSCTL, X_OK))
826 sbin_sysctl = SYSCTL;
829 if (0 == access ("/sbin/sysctl", X_OK))
830 sbin_sysctl = "/sbin/sysctl";
831 else if (0 == access ("/usr/sbin/sysctl", X_OK))
832 sbin_sysctl = "/usr/sbin/sysctl";
836 "Fatal: executable sysctl not found in approved directories: %s\n",
842 /* setup 'mygid' string */
843 snprintf (mygid, sizeof(mygid), "%d", (int) getegid ());
845 /* do not die on SIGPIPE */
846 if (SIG_ERR == signal (SIGPIPE, SIG_IGN))
848 fprintf (stderr, "Failed to protect against SIGPIPE: %s\n",
853 /* setup pipe to shutdown nicely on SIGINT */
854 if (0 != pipe (cpipe))
857 "Fatal: could not setup control pipe: %s\n",
861 if (cpipe[0] >= FD_SETSIZE)
863 fprintf (stderr, "Pipe file descriptor to large: %d", cpipe[0]);
864 (void) close (cpipe[0]);
865 (void) close (cpipe[1]);
869 /* make pipe non-blocking, as we theoretically could otherwise block
870 in the signal handler */
871 int flags = fcntl (cpipe[1], F_GETFL);
874 fprintf (stderr, "Failed to read flags for pipe: %s", strerror (errno));
875 (void) close (cpipe[0]);
876 (void) close (cpipe[1]);
880 if (0 != fcntl (cpipe[1], F_SETFL, flags))
882 fprintf (stderr, "Failed to make pipe non-blocking: %s", strerror (
884 (void) close (cpipe[0]);
885 (void) close (cpipe[1]);
889 if ((SIG_ERR == signal (SIGTERM, &signal_handler)) ||
890 #if (SIGTERM != GNUNET_TERM_SIG)
891 (SIG_ERR == signal (GNUNET_TERM_SIG, &signal_handler)) ||
893 (SIG_ERR == signal (SIGINT, &signal_handler)) ||
894 (SIG_ERR == signal (SIGHUP, &signal_handler)))
897 "Fatal: could not initialize signal handler: %s\n",
899 (void) close (cpipe[0]);
900 (void) close (cpipe[1]);
905 /* get interface name */
906 strncpy (dev, argv[1], IFNAMSIZ);
907 dev[IFNAMSIZ - 1] = '\0';
909 /* Disable rp filtering */
912 char *const sysctl_args[] = { "sysctl", "-w",
913 "net.ipv4.conf.all.rp_filter=0", NULL };
914 char *const sysctl_args2[] = { "sysctl", "-w",
915 "net.ipv4.conf.default.rp_filter=0", NULL };
916 if ((0 != fork_and_exec (sbin_sysctl, sysctl_args)) ||
917 (0 != fork_and_exec (sbin_sysctl, sysctl_args2)))
920 "Failed to disable rp filtering.\n");
926 /* now open virtual interface (first part that requires root) */
927 if (-1 == (fd_tun = init_tun (dev)))
929 fprintf (stderr, "Fatal: could not initialize tun-interface\n");
930 (void) signal (SIGTERM, SIG_IGN);
931 #if (SIGTERM != GNUNET_TERM_SIG)
932 (void) signal (GNUNET_TERM_SIG, SIG_IGN);
934 (void) signal (SIGINT, SIG_IGN);
935 (void) signal (SIGHUP, SIG_IGN);
936 (void) close (cpipe[0]);
937 (void) close (cpipe[1]);
941 /* now set interface addresses */
943 const char *address = argv[2];
944 long prefix_len = atol (argv[3]);
946 if ((prefix_len < 1) || (prefix_len > 127))
948 fprintf (stderr, "Fatal: prefix_len out of range\n");
949 (void) signal (SIGTERM, SIG_IGN);
950 #if (SIGTERM != GNUNET_TERM_SIG)
951 (void) signal (GNUNET_TERM_SIG, SIG_IGN);
953 (void) signal (SIGINT, SIG_IGN);
954 (void) signal (SIGHUP, SIG_IGN);
955 (void) close (cpipe[0]);
956 (void) close (cpipe[1]);
959 set_address6 (dev, address, prefix_len);
963 const char *address = argv[4];
964 const char *mask = argv[5];
966 set_address4 (dev, address, mask);
970 /* update routing tables -- next part why we need SUID! */
971 /* Forward everything from our EGID (which should only be held
972 by the 'gnunet-service-dns') and with destination
973 to port 53 on UDP, without hijacking */
976 r = 8; /* failed to fully setup routing table */
978 char *const mangle_args[] = {
979 "iptables", "-m", "owner", "-t", "mangle", "-I", "OUTPUT", "1", "-p",
980 "udp", "--gid-owner", mygid, "--dport", DNS_PORT, "-j",
983 if (0 != fork_and_exec (sbin_iptables, mangle_args))
987 char *const mangle_args[] = {
988 "ip6tables", "-m", "owner", "-t", "mangle", "-I", "OUTPUT", "1", "-p",
989 "udp", "--gid-owner", mygid, "--dport", DNS_PORT, "-j",
992 if (0 != fork_and_exec (sbin_ip6tables, mangle_args))
993 goto cleanup_mangle_1b;
995 /* Mark all of the other DNS traffic using our mark DNS_MARK,
996 unless it is on a link-local IPv6 address, which we cannot support. */
998 char *const mark_args[] = {
999 "iptables", "-t", "mangle", "-I", "OUTPUT", "2", "-p",
1000 "udp", "--dport", DNS_PORT,
1001 "-j", "MARK", "--set-mark", DNS_MARK,
1004 if (0 != fork_and_exec (sbin_iptables, mark_args))
1005 goto cleanup_mangle_1;
1008 char *const mark_args[] = {
1009 "ip6tables", "-t", "mangle", "-I", "OUTPUT", "2", "-p",
1010 "udp", "--dport", DNS_PORT,
1011 "!", "-s", "fe80::/10", /* this line excludes link-local traffic */
1012 "-j", "MARK", "--set-mark", DNS_MARK,
1015 if (0 != fork_and_exec (sbin_ip6tables, mark_args))
1016 goto cleanup_mark_2b;
1018 /* Forward all marked DNS traffic to our DNS_TABLE */
1020 char *const forward_args[] = {
1021 "ip", "rule", "add", "fwmark", DNS_MARK, "table", DNS_TABLE, NULL
1023 if (0 != fork_and_exec (sbin_ip, forward_args))
1024 goto cleanup_mark_2;
1027 char *const forward_args[] = {
1028 "ip", "-6", "rule", "add", "fwmark", DNS_MARK, "table", DNS_TABLE, NULL
1030 if (0 != fork_and_exec (sbin_ip, forward_args))
1031 goto cleanup_forward_3b;
1033 /* Finally, add rule in our forwarding table to pass to our virtual interface */
1035 char *const route_args[] = {
1036 "ip", "route", "add", "default", "dev", dev,
1037 "table", DNS_TABLE, NULL
1039 if (0 != fork_and_exec (sbin_ip, route_args))
1040 goto cleanup_forward_3;
1043 char *const route_args[] = {
1044 "ip", "-6", "route", "add", "default", "dev", dev,
1045 "table", DNS_TABLE, NULL
1047 if (0 != fork_and_exec (sbin_ip, route_args))
1048 goto cleanup_route_4b;
1052 /* drop privs *except* for the saved UID; this is not perfect, but better
1053 than doing nothing */
1054 #ifdef HAVE_SETRESUID
1055 if (0 != setresuid (uid, uid, 0))
1057 fprintf (stderr, "Failed to setresuid: %s\n", strerror (errno));
1059 goto cleanup_route_4;
1062 /* Note: no 'setuid' here as we must keep our saved UID as root */
1063 if (0 != seteuid (uid))
1065 fprintf (stderr, "Failed to seteuid: %s\n", strerror (errno));
1067 goto cleanup_route_4;
1071 r = 0; /* did fully setup routing table (if nothing else happens, we were successful!) */
1073 /* now forward until we hit a problem */
1076 /* now need to regain privs so we can remove the firewall rules we added! */
1077 #ifdef HAVE_SETRESUID
1078 if (0 != setresuid (uid, 0, 0))
1080 fprintf (stderr, "Failed to setresuid back to root: %s\n", strerror (
1083 goto cleanup_route_4;
1086 if (0 != seteuid (0))
1088 fprintf (stderr, "Failed to seteuid back to root: %s\n", strerror (errno));
1090 goto cleanup_route_4;
1094 /* update routing tables again -- this is why we could not fully drop privs */
1095 /* now undo updating of routing tables; normal exit or clean-up-on-error case */
1099 char *const route_clean_args[] = {
1100 "ip", "-6", "route", "del", "default", "dev", dev,
1101 "table", DNS_TABLE, NULL
1103 if (0 != fork_and_exec (sbin_ip, route_clean_args))
1109 char *const route_clean_args[] = {
1110 "ip", "route", "del", "default", "dev", dev,
1111 "table", DNS_TABLE, NULL
1113 if (0 != fork_and_exec (sbin_ip, route_clean_args))
1119 char *const forward_clean_args[] = {
1120 "ip", "-6", "rule", "del", "fwmark", DNS_MARK, "table", DNS_TABLE, NULL
1122 if (0 != fork_and_exec (sbin_ip, forward_clean_args))
1128 char *const forward_clean_args[] = {
1129 "ip", "rule", "del", "fwmark", DNS_MARK, "table", DNS_TABLE, NULL
1131 if (0 != fork_and_exec (sbin_ip, forward_clean_args))
1137 char *const mark_clean_args[] = {
1138 "ip6tables", "-t", "mangle", "-D", "OUTPUT", "-p", "udp",
1139 "--dport", DNS_PORT,
1140 "!", "-s", "fe80::/10", /* this line excludes link-local traffic */
1141 "-j", "MARK", "--set-mark", DNS_MARK, NULL
1143 if (0 != fork_and_exec (sbin_ip6tables, mark_clean_args))
1149 char *const mark_clean_args[] = {
1150 "iptables", "-t", "mangle", "-D", "OUTPUT", "-p", "udp",
1151 "--dport", DNS_PORT, "-j", "MARK", "--set-mark", DNS_MARK, NULL
1153 if (0 != fork_and_exec (sbin_iptables, mark_clean_args))
1159 char *const mangle_clean_args[] = {
1160 "ip6tables", "-m", "owner", "-t", "mangle", "-D", "OUTPUT", "-p", "udp",
1161 "--gid-owner", mygid, "--dport", DNS_PORT, "-j", "ACCEPT",
1164 if (0 != fork_and_exec (sbin_ip6tables, mangle_clean_args))
1170 char *const mangle_clean_args[] = {
1171 "iptables", "-m", "owner", "-t", "mangle", "-D", "OUTPUT", "-p", "udp",
1172 "--gid-owner", mygid, "--dport", DNS_PORT, "-j", "ACCEPT",
1175 if (0 != fork_and_exec (sbin_iptables, mangle_clean_args))
1180 /* close virtual interface */
1181 (void) close (fd_tun);
1182 /* remove signal handler so we can close the pipes */
1183 (void) signal (SIGTERM, SIG_IGN);
1184 #if (SIGTERM != GNUNET_TERM_SIG)
1185 (void) signal (GNUNET_TERM_SIG, SIG_IGN);
1187 (void) signal (SIGINT, SIG_IGN);
1188 (void) signal (SIGHUP, SIG_IGN);
1189 (void) close (cpipe[0]);
1190 (void) close (cpipe[1]);
1195 /* end of gnunet-helper-dns.c */