diff options
Diffstat (limited to 'fix_options.c')
| -rw-r--r-- | fix_options.c | 109 |
1 files changed, 109 insertions, 0 deletions
diff --git a/fix_options.c b/fix_options.c new file mode 100644 index 0000000..b5e81b8 --- /dev/null +++ b/fix_options.c @@ -0,0 +1,109 @@ + /* + * Routine to disable IP-level socket options. This code was taken from 4.4BSD + * rlogind and kernel source, but all mistakes in it are my fault. + * + * Author: Wietse Venema, Eindhoven University of Technology, The Netherlands. + */ + +#ifndef lint +static char sccsid[] = "@(#) fix_options.c 1.6 97/04/08 02:29:19"; +#endif + +#include <sys/types.h> +#include <sys/param.h> +#include <netinet/in.h> +#include <netinet/in_systm.h> +#include <netinet/ip.h> +#include <netdb.h> +#include <stdio.h> +#include <syslog.h> + +#ifndef IPOPT_OPTVAL +#define IPOPT_OPTVAL 0 +#define IPOPT_OLEN 1 +#endif + +#include "tcpd.h" + +#define BUFFER_SIZE 512 /* Was: BUFSIZ */ + +/* fix_options - get rid of IP-level socket options */ + +fix_options(request) +struct request_info *request; +{ +#ifdef IP_OPTIONS + unsigned char optbuf[BUFFER_SIZE / 3], *cp; + char lbuf[BUFFER_SIZE], *lp; + int optsize = sizeof(optbuf), ipproto; + struct protoent *ip; + int fd = request->fd; + unsigned int opt; + int optlen; + struct in_addr dummy; + + if ((ip = getprotobyname("ip")) != 0) + ipproto = ip->p_proto; + else + ipproto = IPPROTO_IP; + + if (getsockopt(fd, ipproto, IP_OPTIONS, (char *) optbuf, &optsize) == 0 + && optsize != 0) { + + /* + * Horror! 4.[34] BSD getsockopt() prepends the first-hop destination + * address to the result IP options list when source routing options + * are present (see <netinet/ip_var.h>), but produces no output for + * other IP options. Solaris 2.x getsockopt() does produce output for + * non-routing IP options, and uses the same format as BSD even when + * the space for the destination address is unused. The code below + * does the right thing with 4.[34]BSD derivatives and Solaris 2, but + * may occasionally miss source routing options on incompatible + * systems such as Linux. Their choice. + * + * Look for source routing options. Drop the connection when one is + * found. Just wiping the IP options is insufficient: we would still + * help the attacker by providing a real TCP sequence number, and the + * attacker would still be able to send packets (blind spoofing). I + * discussed this attack with Niels Provos, half a year before the + * attack was described in open mailing lists. + * + * It would be cleaner to just return a yes/no reply and let the caller + * decide how to deal with it. Resident servers should not terminate. + * However I am not prepared to make changes to internal interfaces + * on short notice. + */ +#define ADDR_LEN sizeof(dummy.s_addr) + + for (cp = optbuf + ADDR_LEN; cp < optbuf + optsize; cp += optlen) { + opt = cp[IPOPT_OPTVAL]; + if (opt == IPOPT_LSRR || opt == IPOPT_SSRR) { + syslog(LOG_WARNING, + "refused connect from %s with IP source routing options", + eval_client(request)); + shutdown(fd, 2); + return; + } + if (opt == IPOPT_EOL) + break; + if (opt == IPOPT_NOP) { + optlen = 1; + } else { + optlen = cp[IPOPT_OLEN]; + if (optlen <= 0) /* Do not loop! */ + break; + } + } + lp = lbuf; + for (cp = optbuf; optsize > 0; cp++, optsize--, lp += 3) + sprintf(lp, " %2.2x", *cp); + syslog(LOG_NOTICE, + "connect from %s with IP options (ignored):%s", + eval_client(request), lbuf); + if (setsockopt(fd, ipproto, IP_OPTIONS, (char *) 0, optsize) != 0) { + syslog(LOG_ERR, "setsockopt IP_OPTIONS NULL: %m"); + shutdown(fd, 2); + } + } +#endif +} |