* @brief helper to install firewall rules to hijack all DNS traffic
* and send it to our virtual interface (except for DNS traffic
* that originates on the specified port). We then
- * allow interacting with our virtual interface via stdin/stdout.
+ * allow interacting with our virtual interface via stdin/stdout.
* @author Philipp Tölke
* @author Christian Grothoff
*
* administrators must take care to not cause conflicts with these
* values (it was deemed safest to hardcode them as passing these
* values as arguments might permit messing with arbitrary firewall
- * rules, which would be dangerous).
+ * rules, which would be dangerous). Traffic coming from the same
+ * group ID as the effective group ID that this process is running
+ * as is not intercepted.
*
* The code first sets up the virtual interface, then begins to
* redirect the DNS traffic to it, and then on errors or SIGTERM shuts
* Naturally, neither of these problems can be helped as this is the
* fundamental purpose of the binary. Certifying that this code is
* "safe" thus only means that it doesn't allow anything else (such
- * as local priv. escalation, etc.).
+ * as local priv. escalation, etc.).
*
* The following list of people have reviewed this code and considered
* it safe (within specifications) since the last modification (if you
* reviewed it, please have your name added to the list):
*
- * - Christian Grothoff
+ * - Christian Grothoff
*/
#include "platform.h"
/**
* Need 'struct GNUNET_MessageHeader'.
*/
+#include "gnunet_crypto_lib.h"
#include "gnunet_common.h"
/**
/**
* Name and full path of IPTABLES binary.
*/
-#define SBIN_IPTABLES "/sbin/iptables"
+static const char *sbin_iptables;
+
+/**
+ * Name and full path of sysctl binary
+ */
+static const char *sbin_sysctl;
/**
* Name and full path of IPTABLES binary.
*/
-#define SBIN_IP "/sbin/ip"
+static const char *sbin_ip;
/**
* Port for DNS traffic.
}
+/**
+ * Open '/dev/null' and make the result the given
+ * file descriptor.
+ *
+ * @param target_fd desired FD to point to /dev/null
+ * @param flags open flags (O_RDONLY, O_WRONLY)
+ */
+static void
+open_dev_null (int target_fd,
+ int flags)
+{
+ int fd;
+
+ fd = open ("/dev/null", flags);
+ if (-1 == fd)
+ abort ();
+ if (fd == target_fd)
+ return;
+ if (-1 == dup2 (fd, target_fd))
+ {
+ (void) close (fd);
+ abort ();
+ }
+ (void) close (fd);
+}
+
+
/**
* Run the given command and wait for it to complete.
- *
+ *
* @param file name of the binary to run
* @param cmd command line arguments (as given to 'execv')
* @return 0 on success, 1 on any error
*/
static int
-fork_and_exec (const char *file,
+fork_and_exec (const char *file,
char *const cmd[])
{
int status;
pid = fork ();
if (-1 == pid)
{
- fprintf (stderr,
- "fork failed: %s\n",
+ fprintf (stderr,
+ "fork failed: %s\n",
strerror (errno));
return 1;
}
if (0 == pid)
{
/* we are the child process */
+ /* close stdin/stdout to not cause interference
+ with the helper's main protocol! */
+ (void) close (0);
+ open_dev_null (0, O_RDONLY);
+ (void) close (1);
+ open_dev_null (1, O_WRONLY);
(void) execv (file, cmd);
/* can only get here on error */
- fprintf (stderr,
- "exec `%s' failed: %s\n",
+ fprintf (stderr,
+ "exec `%s' failed: %s\n",
file,
strerror (errno));
_exit (1);
}
/* keep running waitpid as long as the only error we get is 'EINTR' */
while ( (-1 == (ret = waitpid (pid, &status, 0))) &&
- (errno == EINTR) );
+ (errno == EINTR) );
if (-1 == ret)
{
- fprintf (stderr,
- "waitpid failed: %s\n",
+ fprintf (stderr,
+ "waitpid failed: %s\n",
strerror (errno));
return 1;
}
if (fd >= FD_SETSIZE)
{
fprintf (stderr, "File descriptor to large: %d", fd);
+ (void) close (fd);
return -1;
}
sa6.sin6_family = AF_INET6;
if (1 != inet_pton (AF_INET6, address, sa6.sin6_addr.s6_addr))
{
- fprintf (stderr, "Failed to parse address `%s': %s\n", address,
+ fprintf (stderr,
+ "Failed to parse IPv6 address `%s': %s\n",
+ address,
strerror (errno));
exit (1);
}
if (-1 == (fd = socket (PF_INET6, SOCK_DGRAM, 0)))
{
- fprintf (stderr, "Error creating socket: %s\n", strerror (errno));
- exit (1);
+ fprintf (stderr,
+ "Error creating IPv6 socket: %s (ignored)\n",
+ strerror (errno));
+ /* ignore error, maybe only IPv4 works on this system! */
+ return;
}
memset (&ifr, 0, sizeof (struct ifreq));
*/
if (1 != inet_pton (AF_INET, address, &addr->sin_addr.s_addr))
{
- fprintf (stderr, "Failed to parse address `%s': %s\n", address,
+ fprintf (stderr,
+ "Failed to parse IPv4 address `%s': %s\n",
+ address,
strerror (errno));
exit (1);
}
if (-1 == (fd = socket (PF_INET, SOCK_DGRAM, 0)))
{
- fprintf (stderr, "Error creating socket: %s\n", strerror (errno));
+ fprintf (stderr,
+ "Error creating IPv4 socket: %s\n",
+ strerror (errno));
exit (1);
}
* We are supposed to read and the buffer is not empty
* -> select on write to stdout
*/
- if (0 != buftun_size)
+ if (0 < buftun_size)
FD_SET (1, &fds_w);
/*
{
if ( (errno == EINTR) ||
(errno == EAGAIN) )
- continue;
+ {
+ buftun_size = 0;
+ continue;
+ }
fprintf (stderr, "read-error: %s\n", strerror (errno));
return;
}
return;
}
buftun_size -= written;
- buftun_read += written;
+ buftun_read += written;
}
if (FD_ISSET (0, &fds_r))
bufin_size = read (0, bufin + bufin_rpos, MAX_SIZE - bufin_rpos);
if (-1 == bufin_size)
{
+ bufin_read = NULL;
if ( (errno == EINTR) ||
(errno == EAGAIN) )
continue;
}
if (0 == bufin_size)
{
+ bufin_read = NULL;
fprintf (stderr, "EOF on stdin\n");
return;
}
* 3: IPv6 netmask length in bits ("64")
* 4: IPv4 address for the tunnel ("1.2.3.4")
* 5: IPv4 netmask ("255.255.0.0")
- * 6: PORT to not hijack ("55533")
* @return 0 on success, otherwise code indicating type of error:
* 1 wrong number of arguments
* 2 invalid arguments (i.e. port number / prefix length wrong)
* 5 failed to initialize tunnel interface
* 6 failed to initialize control pipe
* 8 failed to change routing table, cleanup successful
- * 9-23 failed to undo some changes to routing table
+ * 9-23 failed to change routing table and failed to undo some changes to routing table
* 24 failed to drop privs
* 25-39 failed to drop privs and then failed to undo some changes to routing table
* 40 failed to regain privs
* 41-55 failed to regain prisv and then failed to undo some changes to routing table
+ * 254 insufficient priviledges
* 255 failed to handle kill signal properly
*/
int
main (int argc, char *const*argv)
{
- unsigned int port;
- char localport[6];
int r;
char dev[IFNAMSIZ];
+ char mygid[32];
int fd_tun;
+ uid_t uid;
- if (7 != argc)
+ if (6 != argc)
{
fprintf (stderr, "Fatal: must supply 6 arguments!\n");
return 1;
}
+ /* assert privs so we can modify the firewall rules! */
+ uid = getuid ();
+#ifdef HAVE_SETRESUID
+ if (0 != setresuid (uid, 0, 0))
+ {
+ fprintf (stderr, "Failed to setresuid to root: %s\n", strerror (errno));
+ return 254;
+ }
+#else
+ if (0 != seteuid (0))
+ {
+ fprintf (stderr, "Failed to seteuid back to root: %s\n", strerror (errno));
+ return 254;
+ }
+#endif
+
/* verify that the binaries were care about are executable */
- if (0 != access (SBIN_IPTABLES, X_OK))
+ if (0 == access ("/sbin/iptables", X_OK))
+ sbin_iptables = "/sbin/iptables";
+ else if (0 == access ("/usr/sbin/iptables", X_OK))
+ sbin_iptables = "/usr/sbin/iptables";
+ else
{
- fprintf (stderr,
- "`%s' is not executable: %s\n",
- SBIN_IPTABLES,
+ fprintf (stderr,
+ "Fatal: executable iptables not found in approved directories: %s\n",
strerror (errno));
return 3;
}
- if (0 != access (SBIN_IP, X_OK))
+ if (0 == access ("/sbin/ip", X_OK))
+ sbin_ip = "/sbin/ip";
+ else if (0 == access ("/usr/sbin/ip", X_OK))
+ sbin_ip = "/usr/sbin/ip";
+ else
{
- fprintf (stderr,
- "`%s' is not executable: %s\n",
- SBIN_IP,
+ fprintf (stderr,
+ "Fatal: executable ip not found in approved directories: %s\n",
strerror (errno));
return 4;
}
-
- /* validate port number */
- port = atoi (argv[6]);
- if ( (port == 0) || (port >= 65536) )
+ if (0 == access ("/sbin/sysctl", X_OK))
+ sbin_sysctl = "/sbin/sysctl";
+ else if (0 == access ("/usr/sbin/sysctl", X_OK))
+ sbin_sysctl = "/usr/sbin/sysctl";
+ else
{
- fprintf (stderr,
- "Port `%u' is invalid\n",
- port);
- return 2;
+ fprintf (stderr,
+ "Fatal: executable sysctl not found in approved directories: %s\n",
+ strerror (errno));
+ return 5;
}
- /* print port number to string for command-line use*/
- (void) snprintf (localport,
- sizeof (localport),
- "%u",
- port);
+
+ /* setup 'mygid' string */
+ snprintf (mygid, sizeof (mygid), "%d", (int) getegid());
/* do not die on SIGPIPE */
if (SIG_ERR == signal (SIGPIPE, SIG_IGN))
/* setup pipe to shutdown nicely on SIGINT */
if (0 != pipe (cpipe))
{
- fprintf (stderr,
+ fprintf (stderr,
"Fatal: could not setup control pipe: %s\n",
strerror (errno));
return 6;
return 6;
}
}
- if (SIG_ERR == signal (SIGINT, &signal_handler))
- {
- fprintf (stderr,
+ if ( (SIG_ERR == signal (SIGTERM, &signal_handler)) ||
+#if (SIGTERM != GNUNET_TERM_SIG)
+ (SIG_ERR == signal (GNUNET_TERM_SIG, &signal_handler)) ||
+#endif
+ (SIG_ERR == signal (SIGINT, &signal_handler)) ||
+ (SIG_ERR == signal (SIGHUP, &signal_handler)) )
+ {
+ fprintf (stderr,
"Fatal: could not initialize signal handler: %s\n",
strerror (errno));
(void) close (cpipe[0]);
(void) close (cpipe[1]);
- return 7;
+ return 7;
}
strncpy (dev, argv[1], IFNAMSIZ);
dev[IFNAMSIZ - 1] = '\0';
+ /* Disable rp filtering */
+ {
+ char *const sysctl_args[] = {"sysctl", "-w",
+ "net.ipv4.conf.all.rp_filter=0", NULL};
+ char *const sysctl_args2[] = {"sysctl", "-w",
+ "net.ipv4.conf.default.rp_filter=0", NULL};
+ if ((0 != fork_and_exec (sbin_sysctl, sysctl_args)) ||
+ (0 != fork_and_exec (sbin_sysctl, sysctl_args2)))
+ {
+ fprintf (stderr,
+ "Failed to disable rp filtering.\n");
+ return 5;
+ }
+ }
+
+
/* now open virtual interface (first part that requires root) */
if (-1 == (fd_tun = init_tun (dev)))
{
fprintf (stderr, "Fatal: could not initialize tun-interface\n");
+ (void) signal (SIGTERM, SIG_IGN);
+#if (SIGTERM != GNUNET_TERM_SIG)
+ (void) signal (GNUNET_TERM_SIG, SIG_IGN);
+#endif
(void) signal (SIGINT, SIG_IGN);
+ (void) signal (SIGHUP, SIG_IGN);
(void) close (cpipe[0]);
(void) close (cpipe[1]);
return 5;
if ((prefix_len < 1) || (prefix_len > 127))
{
fprintf (stderr, "Fatal: prefix_len out of range\n");
+ (void) signal (SIGTERM, SIG_IGN);
+#if (SIGTERM != GNUNET_TERM_SIG)
+ (void) signal (GNUNET_TERM_SIG, SIG_IGN);
+#endif
(void) signal (SIGINT, SIG_IGN);
+ (void) signal (SIGHUP, SIG_IGN);
(void) close (cpipe[0]);
(void) close (cpipe[1]);
return 2;
set_address4 (dev, address, mask);
}
-
+
+
/* update routing tables -- next part why we need SUID! */
- /* Forward everything from the given local port (with destination
- to port 53, and only for UDP) without hijacking */
+ /* Forward everything from our EGID (which should only be held
+ by the 'gnunet-service-dns') and with destination
+ to port 53 on UDP, without hijacking */
r = 8; /* failed to fully setup routing table */
{
- char *const mangle_args[] =
+ char *const mangle_args[] =
{
- "iptables", "-t", "mangle", "-I", "OUTPUT", "1", "-p",
- "udp", "--sport", localport, "--dport", DNS_PORT, "-j",
+ "iptables", "-m", "owner", "-t", "mangle", "-I", "OUTPUT", "1", "-p",
+ "udp", "--gid-owner", mygid, "--dport", DNS_PORT, "-j",
"ACCEPT", NULL
};
- if (0 != fork_and_exec (SBIN_IPTABLES, mangle_args))
- goto cleanup_mangle_1;
- }
+ if (0 != fork_and_exec (sbin_iptables, mangle_args))
+ goto cleanup_rest;
+ }
/* Mark all of the other DNS traffic using our mark DNS_MARK */
{
char *const mark_args[] =
{
- "iptables", "-t", "mangle", "-I", "OUTPUT", DNS_TABLE, "-p",
+ "iptables", "-t", "mangle", "-I", "OUTPUT", "2", "-p",
"udp", "--dport", DNS_PORT, "-j", "MARK", "--set-mark", DNS_MARK,
NULL
};
- if (0 != fork_and_exec (SBIN_IPTABLES, mark_args))
- goto cleanup_mark_2;
+ if (0 != fork_and_exec (sbin_iptables, mark_args))
+ goto cleanup_mangle_1;
}
/* Forward all marked DNS traffic to our DNS_TABLE */
{
{
"ip", "rule", "add", "fwmark", DNS_MARK, "table", DNS_TABLE, NULL
};
- if (0 != fork_and_exec (SBIN_IP, forward_args))
- goto cleanup_forward_3;
+ if (0 != fork_and_exec (sbin_ip, forward_args))
+ goto cleanup_mark_2;
}
/* Finally, add rule in our forwarding table to pass to our virtual interface */
{
char *const route_args[] =
{
- "ip", "route", "add", "default", "via", dev,
+ "ip", "route", "add", "default", "dev", dev,
"table", DNS_TABLE, NULL
};
- if (0 != fork_and_exec (SBIN_IP, route_args))
- goto cleanup_route_4;
+ if (0 != fork_and_exec (sbin_ip, route_args))
+ goto cleanup_forward_3;
}
/* drop privs *except* for the saved UID; this is not perfect, but better
than doing nothing */
- uid_t uid = getuid ();
#ifdef HAVE_SETRESUID
if (0 != setresuid (uid, uid, 0))
{
}
#else
/* Note: no 'setuid' here as we must keep our saved UID as root */
- if (0 != seteuid (uid))
+ if (0 != seteuid (uid))
{
fprintf (stderr, "Failed to seteuid: %s\n", strerror (errno));
r = 24;
/* now forward until we hit a problem */
run (fd_tun);
- (void) close (fd_tun);
-
+
/* now need to regain privs so we can remove the firewall rules we added! */
#ifdef HAVE_SETRESUID
if (0 != setresuid (uid, 0, 0))
goto cleanup_route_4;
}
#else
- if (0 != seteuid (0))
+ if (0 != seteuid (0))
{
fprintf (stderr, "Failed to seteuid back to root: %s\n", strerror (errno));
r = 40;
goto cleanup_route_4;
}
#endif
-
+
/* update routing tables again -- this is why we could not fully drop privs */
/* now undo updating of routing tables; normal exit or clean-up-on-error case */
cleanup_route_4:
{
- char *const route_clean_args[] =
+ char *const route_clean_args[] =
{
- "ip", "route", "del", "default", "via", dev,
+ "ip", "route", "del", "default", "dev", dev,
"table", DNS_TABLE, NULL
};
- if (0 != fork_and_exec (SBIN_IP, route_clean_args))
+ if (0 != fork_and_exec (sbin_ip, route_clean_args))
r += 1;
}
cleanup_forward_3:
{
"ip", "rule", "del", "fwmark", DNS_MARK, "table", DNS_TABLE, NULL
};
- if (0 != fork_and_exec (SBIN_IP, forward_clean_args))
+ if (0 != fork_and_exec (sbin_ip, forward_clean_args))
r += 2;
}
cleanup_mark_2:
"iptables", "-t", "mangle", "-D", "OUTPUT", "-p", "udp",
"--dport", DNS_PORT, "-j", "MARK", "--set-mark", DNS_MARK, NULL
};
- if (0 != fork_and_exec (SBIN_IPTABLES, mark_clean_args))
+ if (0 != fork_and_exec (sbin_iptables, mark_clean_args))
r += 4;
}
cleanup_mangle_1:
{
char *const mangle_clean_args[] =
{
- "iptables", "-t", "mangle", "-D", "OUTPUT", "-p", "udp",
- "--sport", localport, "--dport", DNS_PORT, "-j", "ACCEPT",
+ "iptables", "-m", "owner", "-t", "mangle", "-D", "OUTPUT", "-p", "udp",
+ "--gid-owner", mygid, "--dport", DNS_PORT, "-j", "ACCEPT",
NULL
};
- if (0 != fork_and_exec (SBIN_IPTABLES, mangle_clean_args))
+ if (0 != fork_and_exec (sbin_iptables, mangle_clean_args))
r += 8;
}
- /* remove SIGINT handler so we can close the pipes */
+ cleanup_rest:
+ /* close virtual interface */
+ (void) close (fd_tun);
+ /* remove signal handler so we can close the pipes */
+ (void) signal (SIGTERM, SIG_IGN);
+#if (SIGTERM != GNUNET_TERM_SIG)
+ (void) signal (GNUNET_TERM_SIG, SIG_IGN);
+#endif
(void) signal (SIGINT, SIG_IGN);
+ (void) signal (SIGHUP, SIG_IGN);
(void) close (cpipe[0]);
(void) close (cpipe[1]);
return r;
projects / oweals / gnunet.git / blobdiff