Date: Sat, 10 Apr 2004 09:44:25 +0100 From: Bruce M Simpson <bms@spc.org> To: Vlad GALU <dudu@diaspar.rdsnet.ro> Cc: hackers@freebsd.org Subject: Re: passing messages to routing sockets Message-ID: <20040410084425.GT710@empiric.dek.spc.org> In-Reply-To: <20040409195541.I31321@qvnfcne.eqfarg.eb> References: <20040409195541.I31321@qvnfcne.eqfarg.eb>
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On Fri, Apr 09, 2004 at 08:02:30PM +0300, Vlad GALU wrote:
> I understand that in order to add a new route to the routing
> table, one must fill a buffer with an ifa_msghdr header, followed by three
> socked adddress structures, representing the destination net/ip, the
> netmask and the gateway.
[routing table suckiness snipped]
> Could anyone provide a quick/small example on how to fill this
> member ? I don't really understand what I should write into it.
It's a sucky one and I had to stare at src/sbin/route/* for a while til
the penny dropped. The netmasks in particular are packed in in a format
which isn't immediately obvious.
Have a look at the attached code, in particular, reply_rtmsg_resolve().
Also have a look at Section 19.11 of TCP/IP Illustrated Volume 2, and
Section 18.9 of UNIX Network Programming 3e Vol 1.
The API sucks, and it's something we'd like to change in future.
Regards,
BMS
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/* $FreeBSD$ */
/*
* This is a hack to demonstrate the concept of hooking for the
* RTM_RESOLVE message being sent from the FreeBSD routing code,
* as a means of looking up routes on demand using a routing protocol
* such as AODV.
* This code will probably be vastly cleaned up and tested more thoroughly
* before being used as the basis for a user-space BSD AODV implementation.
*/
/*
* Copyright (c) 2003 Bruce M. Simpson <bms@spc.org>
* All rights reserved.
*
* 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, 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.
* 3. All advertising materials mentioning features or use of this software
* must display the following acknowledgement:
* This product includes software developed by Bruce M. Simpson.
* 4. Neither the name of Bruce M. Simpson nor the names of co-
* contributors may be used to endorse or promote products derived
* from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY Bruce M. Simpson AND CONTRIBUTORS
* ``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 Bruce M. Simpson OR CONTRIBUTORS
* 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 <sys/param.h>
#include <sys/file.h>
#include <sys/socket.h>
#include <sys/sysctl.h>
#include <sys/ioctl.h>
#include <sys/sysctl.h>
#include <sys/types.h>
#include <sys/signal.h>
#include <net/if.h>
#include <net/if_var.h>
#include <net/if_mib.h>
#include <net/if_types.h>
#include <net/if_dl.h>
#include <net/route.h>
#include <netinet/in.h>
#include <netinet/if_ether.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <ctype.h>
#include <err.h>
#include <errno.h>
#include <paths.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sysexits.h>
#include <unistd.h>
#include <ifaddrs.h>
union sockunion {
struct sockaddr sa;
struct sockaddr_in sin;
struct sockaddr_dl sdl;
struct sockaddr_storage ss;
};
typedef union sockunion sockunion_t;
void usage(void);
int add_xresolve_route(char *ifname, struct sockaddr_in *sin, int bits);
int inet_cidr_aton(char *s, struct in_addr *pin, int *bits);
int create_if(char *ifname);
int destroy_if(char *ifname);
int if2sockaddr(char *ifname, struct sockaddr_dl *sdl);
int handle_rtmsg(struct rt_msghdr *rtm, int msglen);
int handle_rtmsg_resolve(struct rt_msghdr *rtm, int msglen);
int reply_rtmsg_resolve(struct sockaddr_in *sin);
/*
* We check for the existence of ifname.
*/
#if 1
#define _IFNAME "disc1"
#else
#define _IFNAME "lo0"
#endif
int rtsock = -1;
int created = 0;
char *ifname = _IFNAME;
void
sighand_term(int sig)
{
/*
* Destroying an interface is sufficient to delete the routes
* pointing to it.
*/
if (created)
destroy_if(ifname);
exit(EXIT_SUCCESS);
}
void
setup_signals(void)
{
struct sigaction sa, osa;
sa.sa_handler = sighand_term;
sa.sa_flags = 0;
sigemptyset(&sa.sa_mask);
sigaction(SIGTERM, &sa, &osa);
sigaction(SIGINT, &sa, &osa);
sigaction(SIGQUIT, &sa, &osa);
sigaction(SIGKILL, &sa, &osa);
}
int
main(int argc, char *argv[])
{
int n;
int bits;
char msg[2048];
struct sockaddr_in sin;
if (geteuid() != 0)
errx(1, "must be root to alter routing table");
memset(&sin, 0, sizeof(sin));
sin.sin_family = AF_INET;
sin.sin_len = sizeof(sin);
/* Parse network argument */
if ((argc != 2)
|| (inet_cidr_aton(argv[1], &sin.sin_addr, &bits) != 1))
usage();
setup_signals();
/* Open routing socket */
rtsock = socket(PF_ROUTE, SOCK_RAW, 0);
if (rtsock == -1)
err(EX_OSERR, "socket");
/* Check that the target interface exists; create it if it doesn't. */
if (if_nametoindex(ifname) == 0) {
warnx("interface %s does not exist, creating.", ifname);
create_if(ifname);
created = 1;
add_xresolve_route(ifname, &sin, bits);
}
/* Routing event loop */
for (;;) {
n = read(rtsock, msg, sizeof(msg));
handle_rtmsg((struct rt_msghdr *)msg, n);
}
if (rtsock != -1)
close(rtsock);
exit (EXIT_SUCCESS);
}
void
usage(void)
{
fprintf(stderr, "usage: rtmhack <testnet>\n"
"<testnet> specifies the test network in CIDR notation\n");
exit(EXIT_FAILURE);
}
/*
* Like inet_aton(), but handle an optional CIDR prefix.
*/
int
inet_cidr_aton(char *s, struct in_addr *pin, int *bits)
{
char *q;
q = NULL;
*bits = 32;
if ((q = strchr(s, '/')) != NULL) {
*bits = strtoul(q+1, 0, 0);
*q = '\0';
}
return (inet_aton(s, pin));
}
/*
* create an instance of a named clonable interface.
* Return 0 if successful, or -1 if an error occurred.
*/
int
create_if(char *ifname)
{
int s, retval;
struct ifreq ifr;
retval = 0;
s = socket(AF_INET, SOCK_DGRAM, 0);
if (s == -1)
err(1, "socket");
memset(&ifr, 0, sizeof(ifr));
(void) strlcpy(ifr.ifr_name, ifname, sizeof(ifr.ifr_name));
if (ioctl(s, SIOCIFCREATE, &ifr) < 0) {
retval = -1;
warn("SIOCIFCREATE");
}
close(s);
return (retval);
}
/*
* destroy an instance of a named clonable interface.
* Return 0 if successful, or -1 if an error occurred.
*/
int
destroy_if(char *ifname)
{
int s, retval;
struct ifreq ifr;
retval = 0;
s = socket(AF_INET, SOCK_DGRAM, 0);
if (s == -1)
err(1, "socket");
memset(&ifr, 0, sizeof(ifr));
(void) strlcpy(ifr.ifr_name, ifname, sizeof(ifr.ifr_name));
if (ioctl(s, SIOCIFDESTROY, &ifr) < 0) {
retval = -1;
warn("SIOCIFDESTROY");
}
close(s);
return (retval);
}
/*
* Copy the sockaddr_dl structure corresponding to the named interface
* into the structure pointed to by sdl.
* Returns 0 if successful, or -1 if the structure found was not valid.
*/
int
if2sockaddr(char *ifname, struct sockaddr_dl *sdl)
{
struct ifaddrs *ifap, *ifa;
struct sockaddr_dl *isdl;
if (getifaddrs(&ifap))
err(1, "getifaddrs");
isdl = NULL;
for (ifa = ifap; ifa; ifa = ifa->ifa_next) {
if (ifa->ifa_addr->sa_family != AF_LINK)
continue;
if (strcmp(ifname, ifa->ifa_name))
continue;
isdl = (struct sockaddr_dl *)ifa->ifa_addr;
}
if (isdl)
memcpy(sdl, isdl, isdl->sdl_len);
return ((isdl != NULL) ? 0 : -1);
}
/*
* Given the prefix length of an IPv4 CIDR network address,
* fill out a sockaddr_in structure accordingly for use with
* BSD routing code.
*
* Return the value of the sin_len member as a hint.
*/
int
inet_makenetmask(int bits, struct sockaddr_in *so_mask)
{
char *cp;
unsigned long mask;
int len;
const int maxbits = 32;
memset(so_mask, 0, sizeof(struct sockaddr_in));
mask = 0xFFFFFFFF << (maxbits - bits);
so_mask->sin_addr.s_addr = htonl(mask);
/* count number of bytes in mask containing set bits */
cp = (char *)(&so_mask->sin_addr + 1);
while (*--cp == 0 && cp > (char *)&so_mask)
;
so_mask->sin_len = len = 1 + cp - (char *)&so_mask;
return (len);
}
/*
* Bind an cloning XRESOLVE route, for the given network/host,
* to a named interface.
*
* The packing of the rtm message is all important. The kernel
* expects it in a certain way. This routine seems to work but
* 'route monitor' is reporting some junk at the end of the netmask.
*
* Return 0 if successful, or -1 if an error occurred.
*/
int
add_xresolve_route(char *ifname, struct sockaddr_in *so_dst, int bits)
{
#define ROUNDUP(a) \
((a) > 0 ? (1 + (((a) - 1) | (sizeof(long) - 1))) : sizeof(long))
#define NEXTADDR(cp, l, u) \
do { \
l = (u)->sa.sa_len; \
(l) = ROUNDUP(l); \
memmove((cp), (u), (l)); \
(cp) += (l); \
} while (0)
/* */
struct {
struct rt_msghdr rtm;
sockunion_t addrs[RTAX_MAX];
} r;
sockunion_t so_iface;
sockunion_t so_mask;
int rlen, len, masklen;
char *cp;
cp = (char *)&r.addrs[0];
masklen = rlen = len = 0;
memset(&r, 0, sizeof(r));
memset(&so_iface, 0, sizeof(so_iface));
memset(&so_mask, 0, sizeof(so_mask));
r.rtm.rtm_version = RTM_VERSION;
r.rtm.rtm_type = RTM_ADD;
r.rtm.rtm_pid = getpid();
r.rtm.rtm_seq = 0;
r.rtm.rtm_flags = RTF_XRESOLVE | RTF_CLONING | RTF_UP;
r.rtm.rtm_addrs = RTA_DST | RTA_GATEWAY | RTA_NETMASK;
if2sockaddr(ifname, &so_iface.sdl);
masklen = inet_makenetmask(bits, &so_mask.sin);
NEXTADDR(cp, len, (sockunion_t *)so_dst);
NEXTADDR(cp, len, &so_iface);
NEXTADDR(cp, len, &so_mask);
r.rtm.rtm_msglen = len = cp - (char *)&r;
rlen = write(rtsock, &r, len);
if (rlen < 0)
warn("write");
return ((rlen > 0) ? 0 : -1);
#undef NEXTADDR
#undef ROUNDUP
}
/*
* routing socket message dispatcher
*/
int
handle_rtmsg(struct rt_msghdr *rtm, int msglen)
{
if (rtm->rtm_version != RTM_VERSION) {
(void) printf("bad routing message version %d\n",
rtm->rtm_version);
return (-1);
}
switch (rtm->rtm_type) {
case RTM_RESOLVE:
(void) printf("rtm_type %d: RTM_RESOLVE\n", rtm->rtm_type);
handle_rtmsg_resolve(rtm, msglen);
break;
default:
(void) printf("rtm_type %d: ignored\n", rtm->rtm_type);
}
return (0);
}
/*
* Dispatch routine for RTM_RESOLVE routing messages.
* Return 0 if successful; otherwise, return -1 if an error occurred.
*/
int
handle_rtmsg_resolve(struct rt_msghdr *rtm, int msglen)
{
struct sockaddr_in *sin;
struct sockaddr *sa;
void *sp;
/*
* ignore messages from ourselves
*/
if (rtm->rtm_pid == getpid()) {
printf("heard own message, ignoring\n");
return (0);
}
printf("rtm_index: %04x rtm_addrs: %08x\n",
rtm->rtm_index, rtm->rtm_addrs);
/*
* The message must contain the address for which a route is
* being requested, otherwise it is invalid.
*/
if (!(rtm->rtm_addrs & RTA_DST)) {
warnx("RTM_RESOLVE message does not contain destination");
return (-1);
}
sa = sp = (rtm + 1);
if (sa->sa_family != AF_INET) {
warnx("RTM_RESOLVE contains non-AF_INET destination %d",
sa->sa_family);
return (-1);
}
sin = (struct sockaddr_in *)sa;
printf("route requested for %s\n", inet_ntoa(sin->sin_addr));
/*
* XXX: Should check if the requested destination is within the
* network prefix specified on the command line.
*/
reply_rtmsg_resolve(sin);
printf("route resolved for %s\n", inet_ntoa(sin->sin_addr));
return (0);
}
/*
* Modify a given route in response to an RTM_RESOLVE message from the kernel.
* Return 0 if successful; otherwise, return -1.
*/
int
reply_rtmsg_resolve(struct sockaddr_in *sin)
{
struct {
struct rt_msghdr rtm;
struct sockaddr addrs[RTAX_MAX];
} r;
struct sockaddr_dl sdl;
int len;
memset(&r, 0, sizeof(r));
r.rtm.rtm_version = RTM_VERSION;
r.rtm.rtm_type = RTM_CHANGE;
r.rtm.rtm_pid = getpid();
r.rtm.rtm_seq = 0;
if2sockaddr("lo0", &sdl);
memcpy(&r.addrs[RTAX_DST], sin, sin->sin_len);
memcpy(&r.addrs[RTAX_GATEWAY], &sdl, sdl.sdl_len);
memset(&r.addrs[RTAX_IFP], 0, sizeof(r.addrs[RTAX_IFP]));
memset(&r.addrs[RTAX_IFA], 0, sizeof(r.addrs[RTAX_IFA]));
r.rtm.rtm_addrs = RTA_DST | RTA_GATEWAY | RTA_IFP | RTA_IFA;
r.rtm.rtm_flags = RTF_DONE;
r.rtm.rtm_msglen = sizeof(r);
len = write(rtsock, &r, r.rtm.rtm_msglen);
if (len != r.rtm.rtm_msglen)
warn("write");
return ((len > 0) ? 0 : -1);
}
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