From 11eeef41d5f63c7d2f7fdfcc733eb7fb137cc384 Mon Sep 17 00:00:00 2001 From: Evgeniy Polyakov Date: Mon, 8 Jun 2009 17:01:51 +0200 Subject: netfilter: passive OS fingerprint xtables match Passive OS fingerprinting netfilter module allows to passively detect remote OS and perform various netfilter actions based on that knowledge. This module compares some data (WS, MSS, options and it's order, ttl, df and others) from packets with SYN bit set with dynamically loaded OS fingerprints. Fingerprint matching rules can be downloaded from OpenBSD source tree or found in archive and loaded via netfilter netlink subsystem into the kernel via special util found in archive. Archive contains library file (also attached), which was shipped with iptables extensions some time ago (at least when ipt_osf existed in patch-o-matic). Following changes were made in this release: * added NLM_F_CREATE/NLM_F_EXCL checks * dropped _rcu list traversing helpers in the protected add/remove calls * dropped unneded structures, debug prints, obscure comment and check Fingerprints can be downloaded from http://www.openbsd.org/cgi-bin/cvsweb/src/etc/pf.os or can be found in archive Example usage: -d switch removes fingerprints Please consider for inclusion. Thank you. Passive OS fingerprint homepage (archives, examples): http://www.ioremap.net/projects/osf Signed-off-by: Evgeniy Polyakov Signed-off-by: Patrick McHardy --- net/netfilter/Kconfig | 13 ++ net/netfilter/Makefile | 1 + net/netfilter/xt_osf.c | 428 +++++++++++++++++++++++++++++++++++++++++++++++++ 3 files changed, 442 insertions(+) create mode 100644 net/netfilter/xt_osf.c (limited to 'net') diff --git a/net/netfilter/Kconfig b/net/netfilter/Kconfig index cb3ad74..79ba47f 100644 --- a/net/netfilter/Kconfig +++ b/net/netfilter/Kconfig @@ -917,6 +917,19 @@ config NETFILTER_XT_MATCH_U32 Details and examples are in the kernel module source. +config NETFILTER_XT_MATCH_OSF + tristate '"osf" Passive OS fingerprint match' + depends on NETFILTER_ADVANCED && NETFILTER_NETLINK + help + This option selects the Passive OS Fingerprinting match module + that allows to passively match the remote operating system by + analyzing incoming TCP SYN packets. + + Rules and loading software can be downloaded from + http://www.ioremap.net/projects/osf + + To compile it as a module, choose M here. If unsure, say N. + endif # NETFILTER_XTABLES endmenu diff --git a/net/netfilter/Makefile b/net/netfilter/Makefile index 6282060..49f62ee 100644 --- a/net/netfilter/Makefile +++ b/net/netfilter/Makefile @@ -77,6 +77,7 @@ obj-$(CONFIG_NETFILTER_XT_MATCH_LIMIT) += xt_limit.o obj-$(CONFIG_NETFILTER_XT_MATCH_MAC) += xt_mac.o obj-$(CONFIG_NETFILTER_XT_MATCH_MARK) += xt_mark.o obj-$(CONFIG_NETFILTER_XT_MATCH_MULTIPORT) += xt_multiport.o +obj-$(CONFIG_NETFILTER_XT_MATCH_OSF) += xt_osf.o obj-$(CONFIG_NETFILTER_XT_MATCH_OWNER) += xt_owner.o obj-$(CONFIG_NETFILTER_XT_MATCH_PHYSDEV) += xt_physdev.o obj-$(CONFIG_NETFILTER_XT_MATCH_PKTTYPE) += xt_pkttype.o diff --git a/net/netfilter/xt_osf.c b/net/netfilter/xt_osf.c new file mode 100644 index 0000000..863e409 --- /dev/null +++ b/net/netfilter/xt_osf.c @@ -0,0 +1,428 @@ +/* + * Copyright (c) 2003+ Evgeniy Polyakov + * + * + * 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., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA + */ + +#include +#include + +#include +#include +#include +#include +#include +#include +#include +#include + +#include +#include + +#include +#include +#include +#include + +struct xt_osf_finger { + struct rcu_head rcu_head; + struct list_head finger_entry; + struct xt_osf_user_finger finger; +}; + +enum osf_fmatch_states { + /* Packet does not match the fingerprint */ + FMATCH_WRONG = 0, + /* Packet matches the fingerprint */ + FMATCH_OK, + /* Options do not match the fingerprint, but header does */ + FMATCH_OPT_WRONG, +}; + +/* + * Indexed by dont-fragment bit. + * It is the only constant value in the fingerprint. + */ +static struct list_head xt_osf_fingers[2]; + +static const struct nla_policy xt_osf_policy[OSF_ATTR_MAX + 1] = { + [OSF_ATTR_FINGER] = { .len = sizeof(struct xt_osf_user_finger) }, +}; + +static void xt_osf_finger_free_rcu(struct rcu_head *rcu_head) +{ + struct xt_osf_finger *f = container_of(rcu_head, struct xt_osf_finger, rcu_head); + + kfree(f); +} + +static int xt_osf_add_callback(struct sock *ctnl, struct sk_buff *skb, + struct nlmsghdr *nlh, struct nlattr *osf_attrs[]) +{ + struct xt_osf_user_finger *f; + struct xt_osf_finger *kf = NULL, *sf; + int err = 0; + + if (!osf_attrs[OSF_ATTR_FINGER]) + return -EINVAL; + + if (!(nlh->nlmsg_flags & NLM_F_CREATE)) + return -EINVAL; + + f = nla_data(osf_attrs[OSF_ATTR_FINGER]); + + kf = kmalloc(sizeof(struct xt_osf_finger), GFP_KERNEL); + if (!kf) + return -ENOMEM; + + memcpy(&kf->finger, f, sizeof(struct xt_osf_user_finger)); + + list_for_each_entry(sf, &xt_osf_fingers[!!f->df], finger_entry) { + if (memcmp(&sf->finger, f, sizeof(struct xt_osf_user_finger))) + continue; + + kfree(kf); + kf = NULL; + + if (nlh->nlmsg_flags & NLM_F_EXCL) + err = -EEXIST; + break; + } + + /* + * We are protected by nfnl mutex. + */ + if (kf) + list_add_tail_rcu(&kf->finger_entry, &xt_osf_fingers[!!f->df]); + + return err; +} + +static int xt_osf_remove_callback(struct sock *ctnl, struct sk_buff *skb, + struct nlmsghdr *nlh, struct nlattr *osf_attrs[]) +{ + struct xt_osf_user_finger *f; + struct xt_osf_finger *sf; + int err = ENOENT; + + if (!osf_attrs[OSF_ATTR_FINGER]) + return -EINVAL; + + f = nla_data(osf_attrs[OSF_ATTR_FINGER]); + + list_for_each_entry(sf, &xt_osf_fingers[!!f->df], finger_entry) { + if (memcmp(&sf->finger, f, sizeof(struct xt_osf_user_finger))) + continue; + + /* + * We are protected by nfnl mutex. + */ + list_del_rcu(&sf->finger_entry); + call_rcu(&sf->rcu_head, xt_osf_finger_free_rcu); + + err = 0; + break; + } + + return err; +} + +static const struct nfnl_callback xt_osf_nfnetlink_callbacks[OSF_MSG_MAX] = { + [OSF_MSG_ADD] = { + .call = xt_osf_add_callback, + .attr_count = OSF_ATTR_MAX, + .policy = xt_osf_policy, + }, + [OSF_MSG_REMOVE] = { + .call = xt_osf_remove_callback, + .attr_count = OSF_ATTR_MAX, + .policy = xt_osf_policy, + }, +}; + +static const struct nfnetlink_subsystem xt_osf_nfnetlink = { + .name = "osf", + .subsys_id = NFNL_SUBSYS_OSF, + .cb_count = OSF_MSG_MAX, + .cb = xt_osf_nfnetlink_callbacks, +}; + +static inline int xt_osf_ttl(const struct sk_buff *skb, const struct xt_osf_info *info, + unsigned char f_ttl) +{ + const struct iphdr *ip = ip_hdr(skb); + + if (info->flags & XT_OSF_TTL) { + if (info->ttl == XT_OSF_TTL_TRUE) + return ip->ttl == f_ttl; + if (info->ttl == XT_OSF_TTL_NOCHECK) + return 1; + else if (ip->ttl <= f_ttl) + return 1; + else { + struct in_device *in_dev = __in_dev_get_rcu(skb->dev); + int ret = 0; + + for_ifa(in_dev) { + if (inet_ifa_match(ip->saddr, ifa)) { + ret = (ip->ttl == f_ttl); + break; + } + } + endfor_ifa(in_dev); + + return ret; + } + } + + return ip->ttl == f_ttl; +} + +static bool xt_osf_match_packet(const struct sk_buff *skb, + const struct xt_match_param *p) +{ + const struct xt_osf_info *info = p->matchinfo; + const struct iphdr *ip = ip_hdr(skb); + const struct tcphdr *tcp; + struct tcphdr _tcph; + int fmatch = FMATCH_WRONG, fcount = 0; + unsigned int optsize = 0, check_WSS = 0; + u16 window, totlen, mss = 0; + bool df; + const unsigned char *optp = NULL, *_optp = NULL; + unsigned char opts[MAX_IPOPTLEN]; + const struct xt_osf_finger *kf; + const struct xt_osf_user_finger *f; + + if (!info) + return false; + + tcp = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(struct tcphdr), &_tcph); + if (!tcp) + return false; + + if (!tcp->syn) + return false; + + totlen = ntohs(ip->tot_len); + df = ntohs(ip->frag_off) & IP_DF; + window = ntohs(tcp->window); + + if (tcp->doff * 4 > sizeof(struct tcphdr)) { + optsize = tcp->doff * 4 - sizeof(struct tcphdr); + + _optp = optp = skb_header_pointer(skb, ip_hdrlen(skb) + + sizeof(struct tcphdr), optsize, opts); + } + + rcu_read_lock(); + list_for_each_entry_rcu(kf, &xt_osf_fingers[df], finger_entry) { + f = &kf->finger; + + if (!(info->flags & XT_OSF_LOG) && strcmp(info->genre, f->genre)) + continue; + + optp = _optp; + fmatch = FMATCH_WRONG; + + if (totlen == f->ss && xt_osf_ttl(skb, info, f->ttl)) { + int foptsize, optnum; + + /* + * Should not happen if userspace parser was written correctly. + */ + if (f->wss.wc >= OSF_WSS_MAX) + continue; + + /* Check options */ + + foptsize = 0; + for (optnum = 0; optnum < f->opt_num; ++optnum) + foptsize += f->opt[optnum].length; + + if (foptsize > MAX_IPOPTLEN || + optsize > MAX_IPOPTLEN || + optsize != foptsize) + continue; + + check_WSS = f->wss.wc; + + for (optnum = 0; optnum < f->opt_num; ++optnum) { + if (f->opt[optnum].kind == (*optp)) { + __u32 len = f->opt[optnum].length; + const __u8 *optend = optp + len; + int loop_cont = 0; + + fmatch = FMATCH_OK; + + switch (*optp) { + case OSFOPT_MSS: + mss = optp[3]; + mss <<= 8; + mss |= optp[2]; + + mss = ntohs(mss); + break; + case OSFOPT_TS: + loop_cont = 1; + break; + } + + optp = optend; + } else + fmatch = FMATCH_OPT_WRONG; + + if (fmatch != FMATCH_OK) + break; + } + + if (fmatch != FMATCH_OPT_WRONG) { + fmatch = FMATCH_WRONG; + + switch (check_WSS) { + case OSF_WSS_PLAIN: + if (f->wss.val == 0 || window == f->wss.val) + fmatch = FMATCH_OK; + break; + case OSF_WSS_MSS: + /* + * Some smart modems decrease mangle MSS to + * SMART_MSS_2, so we check standard, decreased + * and the one provided in the fingerprint MSS + * values. + */ +#define SMART_MSS_1 1460 +#define SMART_MSS_2 1448 + if (window == f->wss.val * mss || + window == f->wss.val * SMART_MSS_1 || + window == f->wss.val * SMART_MSS_2) + fmatch = FMATCH_OK; + break; + case OSF_WSS_MTU: + if (window == f->wss.val * (mss + 40) || + window == f->wss.val * (SMART_MSS_1 + 40) || + window == f->wss.val * (SMART_MSS_2 + 40)) + fmatch = FMATCH_OK; + break; + case OSF_WSS_MODULO: + if ((window % f->wss.val) == 0) + fmatch = FMATCH_OK; + break; + } + } + + if (fmatch != FMATCH_OK) + continue; + + fcount++; + + if (info->flags & XT_OSF_LOG) + nf_log_packet(p->hooknum, 0, skb, p->in, p->out, NULL, + "%s [%s:%s] : %pi4:%d -> %pi4:%d hops=%d\n", + f->genre, f->version, f->subtype, + &ip->saddr, ntohs(tcp->source), + &ip->daddr, ntohs(tcp->dest), + f->ttl - ip->ttl); + + if ((info->flags & XT_OSF_LOG) && + info->loglevel == XT_OSF_LOGLEVEL_FIRST) + break; + } + } + rcu_read_unlock(); + + if (!fcount && (info->flags & XT_OSF_LOG)) + nf_log_packet(p->hooknum, 0, skb, p->in, p->out, NULL, + "Remote OS is not known: %pi4:%u -> %pi4:%u\n", + &ip->saddr, ntohs(tcp->source), + &ip->daddr, ntohs(tcp->dest)); + + if (fcount) + fmatch = FMATCH_OK; + + return fmatch == FMATCH_OK; +} + +static struct xt_match xt_osf_match = { + .name = "osf", + .revision = 0, + .family = NFPROTO_IPV4, + .proto = IPPROTO_TCP, + .hooks = (1 << NF_INET_LOCAL_IN) | + (1 << NF_INET_PRE_ROUTING) | + (1 << NF_INET_FORWARD), + .match = xt_osf_match_packet, + .matchsize = sizeof(struct xt_osf_info), + .me = THIS_MODULE, +}; + +static int __init xt_osf_init(void) +{ + int err = -EINVAL; + int i; + + for (i=0; ifinger_entry); + call_rcu(&f->rcu_head, xt_osf_finger_free_rcu); + } + } + rcu_read_unlock(); + + rcu_barrier(); +} + +module_init(xt_osf_init); +module_exit(xt_osf_fini); + +MODULE_LICENSE("GPL"); +MODULE_AUTHOR("Evgeniy Polyakov "); +MODULE_DESCRIPTION("Passive OS fingerprint matching."); +MODULE_ALIAS_NFNL_SUBSYS(NFNL_SUBSYS_OSF); -- cgit v1.1