/* * Copyright (c) 2003+ Evgeniy Polyakov <zbr@ioremap.net> * * * 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 */ #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt #include <linux/module.h> #include <linux/kernel.h> #include <linux/if.h> #include <linux/inetdevice.h> #include <linux/ip.h> #include <linux/list.h> #include <linux/rculist.h> #include <linux/skbuff.h> #include <linux/slab.h> #include <linux/tcp.h> #include <net/ip.h> #include <net/tcp.h> #include <linux/netfilter/nfnetlink.h> #include <linux/netfilter/x_tables.h> #include <net/netfilter/nf_log.h> #include <linux/netfilter/xt_osf.h> 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 int xt_osf_add_callback(struct sock *ctnl, struct sk_buff *skb, const struct nlmsghdr *nlh, const struct nlattr * const 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, const struct nlmsghdr *nlh, const struct nlattr * const 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); kfree_rcu(sf, rcu_head); 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, struct xt_action_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->family, p->hooknum, 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->family, p->hooknum, 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; i<ARRAY_SIZE(xt_osf_fingers); ++i) INIT_LIST_HEAD(&xt_osf_fingers[i]); err = nfnetlink_subsys_register(&xt_osf_nfnetlink); if (err < 0) { pr_err("Failed to register OSF nsfnetlink helper (%d)\n", err); goto err_out_exit; } err = xt_register_match(&xt_osf_match); if (err) { pr_err("Failed to register OS fingerprint " "matching module (%d)\n", err); goto err_out_remove; } return 0; err_out_remove: nfnetlink_subsys_unregister(&xt_osf_nfnetlink); err_out_exit: return err; } static void __exit xt_osf_fini(void) { struct xt_osf_finger *f; int i; nfnetlink_subsys_unregister(&xt_osf_nfnetlink); xt_unregister_match(&xt_osf_match); rcu_read_lock(); for (i=0; i<ARRAY_SIZE(xt_osf_fingers); ++i) { list_for_each_entry_rcu(f, &xt_osf_fingers[i], finger_entry) { list_del_rcu(&f->finger_entry); kfree_rcu(f, rcu_head); } } rcu_read_unlock(); rcu_barrier(); } module_init(xt_osf_init); module_exit(xt_osf_fini); MODULE_LICENSE("GPL"); MODULE_AUTHOR("Evgeniy Polyakov <zbr@ioremap.net>"); MODULE_DESCRIPTION("Passive OS fingerprint matching."); MODULE_ALIAS_NFNL_SUBSYS(NFNL_SUBSYS_OSF);