916a27901d
The capability check in nfnetlink_rcv() verifies that the caller has CAP_NET_ADMIN in the namespace that "owns" the netlink socket. However, xt_osf_fingers is shared by all net namespaces on the system. An unprivileged user can create user and net namespaces in which he holds CAP_NET_ADMIN to bypass the netlink_net_capable() check: vpnns -- nfnl_osf -f /tmp/pf.os vpnns -- nfnl_osf -f /tmp/pf.os -d These non-root operations successfully modify the systemwide OS fingerprint list. Add new capable() checks so that they can't. Signed-off-by: Kevin Cernekee <cernekee@chromium.org> Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
435 lines
10 KiB
C
435 lines
10 KiB
C
/*
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* Copyright (c) 2003+ Evgeniy Polyakov <zbr@ioremap.net>
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*
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, see <http://www.gnu.org/licenses/>.
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*/
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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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#include <linux/module.h>
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#include <linux/kernel.h>
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#include <linux/capability.h>
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#include <linux/if.h>
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#include <linux/inetdevice.h>
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#include <linux/ip.h>
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#include <linux/list.h>
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#include <linux/rculist.h>
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#include <linux/skbuff.h>
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#include <linux/slab.h>
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#include <linux/tcp.h>
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#include <net/ip.h>
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#include <net/tcp.h>
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#include <linux/netfilter/nfnetlink.h>
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#include <linux/netfilter/x_tables.h>
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#include <net/netfilter/nf_log.h>
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#include <linux/netfilter/xt_osf.h>
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struct xt_osf_finger {
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struct rcu_head rcu_head;
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struct list_head finger_entry;
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struct xt_osf_user_finger finger;
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};
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enum osf_fmatch_states {
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/* Packet does not match the fingerprint */
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FMATCH_WRONG = 0,
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/* Packet matches the fingerprint */
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FMATCH_OK,
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/* Options do not match the fingerprint, but header does */
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FMATCH_OPT_WRONG,
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};
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/*
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* Indexed by dont-fragment bit.
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* It is the only constant value in the fingerprint.
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*/
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static struct list_head xt_osf_fingers[2];
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static const struct nla_policy xt_osf_policy[OSF_ATTR_MAX + 1] = {
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[OSF_ATTR_FINGER] = { .len = sizeof(struct xt_osf_user_finger) },
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};
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static int xt_osf_add_callback(struct net *net, struct sock *ctnl,
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struct sk_buff *skb, const struct nlmsghdr *nlh,
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const struct nlattr * const osf_attrs[],
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struct netlink_ext_ack *extack)
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{
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struct xt_osf_user_finger *f;
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struct xt_osf_finger *kf = NULL, *sf;
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int err = 0;
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if (!capable(CAP_NET_ADMIN))
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return -EPERM;
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if (!osf_attrs[OSF_ATTR_FINGER])
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return -EINVAL;
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if (!(nlh->nlmsg_flags & NLM_F_CREATE))
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return -EINVAL;
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f = nla_data(osf_attrs[OSF_ATTR_FINGER]);
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kf = kmalloc(sizeof(struct xt_osf_finger), GFP_KERNEL);
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if (!kf)
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return -ENOMEM;
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memcpy(&kf->finger, f, sizeof(struct xt_osf_user_finger));
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list_for_each_entry(sf, &xt_osf_fingers[!!f->df], finger_entry) {
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if (memcmp(&sf->finger, f, sizeof(struct xt_osf_user_finger)))
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continue;
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kfree(kf);
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kf = NULL;
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if (nlh->nlmsg_flags & NLM_F_EXCL)
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err = -EEXIST;
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break;
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}
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/*
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* We are protected by nfnl mutex.
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*/
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if (kf)
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list_add_tail_rcu(&kf->finger_entry, &xt_osf_fingers[!!f->df]);
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return err;
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}
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static int xt_osf_remove_callback(struct net *net, struct sock *ctnl,
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struct sk_buff *skb,
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const struct nlmsghdr *nlh,
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const struct nlattr * const osf_attrs[],
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struct netlink_ext_ack *extack)
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{
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struct xt_osf_user_finger *f;
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struct xt_osf_finger *sf;
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int err = -ENOENT;
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if (!capable(CAP_NET_ADMIN))
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return -EPERM;
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if (!osf_attrs[OSF_ATTR_FINGER])
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return -EINVAL;
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f = nla_data(osf_attrs[OSF_ATTR_FINGER]);
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list_for_each_entry(sf, &xt_osf_fingers[!!f->df], finger_entry) {
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if (memcmp(&sf->finger, f, sizeof(struct xt_osf_user_finger)))
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continue;
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/*
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* We are protected by nfnl mutex.
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*/
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list_del_rcu(&sf->finger_entry);
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kfree_rcu(sf, rcu_head);
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err = 0;
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break;
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}
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return err;
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}
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static const struct nfnl_callback xt_osf_nfnetlink_callbacks[OSF_MSG_MAX] = {
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[OSF_MSG_ADD] = {
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.call = xt_osf_add_callback,
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.attr_count = OSF_ATTR_MAX,
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.policy = xt_osf_policy,
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},
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[OSF_MSG_REMOVE] = {
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.call = xt_osf_remove_callback,
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.attr_count = OSF_ATTR_MAX,
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.policy = xt_osf_policy,
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},
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};
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static const struct nfnetlink_subsystem xt_osf_nfnetlink = {
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.name = "osf",
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.subsys_id = NFNL_SUBSYS_OSF,
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.cb_count = OSF_MSG_MAX,
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.cb = xt_osf_nfnetlink_callbacks,
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};
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static inline int xt_osf_ttl(const struct sk_buff *skb, const struct xt_osf_info *info,
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unsigned char f_ttl)
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{
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const struct iphdr *ip = ip_hdr(skb);
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if (info->flags & XT_OSF_TTL) {
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if (info->ttl == XT_OSF_TTL_TRUE)
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return ip->ttl == f_ttl;
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if (info->ttl == XT_OSF_TTL_NOCHECK)
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return 1;
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else if (ip->ttl <= f_ttl)
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return 1;
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else {
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struct in_device *in_dev = __in_dev_get_rcu(skb->dev);
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int ret = 0;
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for_ifa(in_dev) {
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if (inet_ifa_match(ip->saddr, ifa)) {
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ret = (ip->ttl == f_ttl);
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break;
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}
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}
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endfor_ifa(in_dev);
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return ret;
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}
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}
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return ip->ttl == f_ttl;
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}
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static bool
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xt_osf_match_packet(const struct sk_buff *skb, struct xt_action_param *p)
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{
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const struct xt_osf_info *info = p->matchinfo;
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const struct iphdr *ip = ip_hdr(skb);
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const struct tcphdr *tcp;
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struct tcphdr _tcph;
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int fmatch = FMATCH_WRONG, fcount = 0;
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unsigned int optsize = 0, check_WSS = 0;
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u16 window, totlen, mss = 0;
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bool df;
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const unsigned char *optp = NULL, *_optp = NULL;
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unsigned char opts[MAX_IPOPTLEN];
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const struct xt_osf_finger *kf;
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const struct xt_osf_user_finger *f;
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struct net *net = xt_net(p);
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if (!info)
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return false;
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tcp = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(struct tcphdr), &_tcph);
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if (!tcp)
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return false;
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if (!tcp->syn)
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return false;
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totlen = ntohs(ip->tot_len);
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df = ntohs(ip->frag_off) & IP_DF;
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window = ntohs(tcp->window);
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if (tcp->doff * 4 > sizeof(struct tcphdr)) {
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optsize = tcp->doff * 4 - sizeof(struct tcphdr);
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_optp = optp = skb_header_pointer(skb, ip_hdrlen(skb) +
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sizeof(struct tcphdr), optsize, opts);
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}
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list_for_each_entry_rcu(kf, &xt_osf_fingers[df], finger_entry) {
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int foptsize, optnum;
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f = &kf->finger;
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if (!(info->flags & XT_OSF_LOG) && strcmp(info->genre, f->genre))
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continue;
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optp = _optp;
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fmatch = FMATCH_WRONG;
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if (totlen != f->ss || !xt_osf_ttl(skb, info, f->ttl))
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continue;
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/*
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* Should not happen if userspace parser was written correctly.
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*/
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if (f->wss.wc >= OSF_WSS_MAX)
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continue;
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/* Check options */
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foptsize = 0;
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for (optnum = 0; optnum < f->opt_num; ++optnum)
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foptsize += f->opt[optnum].length;
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if (foptsize > MAX_IPOPTLEN ||
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optsize > MAX_IPOPTLEN ||
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optsize != foptsize)
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continue;
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check_WSS = f->wss.wc;
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for (optnum = 0; optnum < f->opt_num; ++optnum) {
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if (f->opt[optnum].kind == (*optp)) {
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__u32 len = f->opt[optnum].length;
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const __u8 *optend = optp + len;
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fmatch = FMATCH_OK;
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switch (*optp) {
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case OSFOPT_MSS:
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mss = optp[3];
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mss <<= 8;
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mss |= optp[2];
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mss = ntohs((__force __be16)mss);
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break;
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case OSFOPT_TS:
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break;
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}
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optp = optend;
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} else
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fmatch = FMATCH_OPT_WRONG;
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if (fmatch != FMATCH_OK)
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break;
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}
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if (fmatch != FMATCH_OPT_WRONG) {
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fmatch = FMATCH_WRONG;
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switch (check_WSS) {
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case OSF_WSS_PLAIN:
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if (f->wss.val == 0 || window == f->wss.val)
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fmatch = FMATCH_OK;
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break;
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case OSF_WSS_MSS:
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/*
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* Some smart modems decrease mangle MSS to
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* SMART_MSS_2, so we check standard, decreased
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* and the one provided in the fingerprint MSS
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* values.
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*/
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#define SMART_MSS_1 1460
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#define SMART_MSS_2 1448
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if (window == f->wss.val * mss ||
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window == f->wss.val * SMART_MSS_1 ||
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window == f->wss.val * SMART_MSS_2)
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fmatch = FMATCH_OK;
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break;
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case OSF_WSS_MTU:
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if (window == f->wss.val * (mss + 40) ||
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window == f->wss.val * (SMART_MSS_1 + 40) ||
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window == f->wss.val * (SMART_MSS_2 + 40))
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fmatch = FMATCH_OK;
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break;
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case OSF_WSS_MODULO:
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if ((window % f->wss.val) == 0)
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fmatch = FMATCH_OK;
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break;
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}
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}
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if (fmatch != FMATCH_OK)
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continue;
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fcount++;
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if (info->flags & XT_OSF_LOG)
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nf_log_packet(net, xt_family(p), xt_hooknum(p), skb,
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xt_in(p), xt_out(p), NULL,
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"%s [%s:%s] : %pI4:%d -> %pI4:%d hops=%d\n",
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f->genre, f->version, f->subtype,
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&ip->saddr, ntohs(tcp->source),
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&ip->daddr, ntohs(tcp->dest),
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f->ttl - ip->ttl);
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if ((info->flags & XT_OSF_LOG) &&
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info->loglevel == XT_OSF_LOGLEVEL_FIRST)
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break;
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}
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if (!fcount && (info->flags & XT_OSF_LOG))
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nf_log_packet(net, xt_family(p), xt_hooknum(p), skb, xt_in(p),
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xt_out(p), NULL,
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"Remote OS is not known: %pI4:%u -> %pI4:%u\n",
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&ip->saddr, ntohs(tcp->source),
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&ip->daddr, ntohs(tcp->dest));
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if (fcount)
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fmatch = FMATCH_OK;
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return fmatch == FMATCH_OK;
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}
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static struct xt_match xt_osf_match = {
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.name = "osf",
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.revision = 0,
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.family = NFPROTO_IPV4,
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.proto = IPPROTO_TCP,
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.hooks = (1 << NF_INET_LOCAL_IN) |
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(1 << NF_INET_PRE_ROUTING) |
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(1 << NF_INET_FORWARD),
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.match = xt_osf_match_packet,
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.matchsize = sizeof(struct xt_osf_info),
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.me = THIS_MODULE,
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};
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static int __init xt_osf_init(void)
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{
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int err = -EINVAL;
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int i;
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for (i=0; i<ARRAY_SIZE(xt_osf_fingers); ++i)
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INIT_LIST_HEAD(&xt_osf_fingers[i]);
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err = nfnetlink_subsys_register(&xt_osf_nfnetlink);
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if (err < 0) {
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pr_err("Failed to register OSF nsfnetlink helper (%d)\n", err);
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goto err_out_exit;
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}
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err = xt_register_match(&xt_osf_match);
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if (err) {
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pr_err("Failed to register OS fingerprint "
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"matching module (%d)\n", err);
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goto err_out_remove;
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}
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return 0;
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err_out_remove:
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nfnetlink_subsys_unregister(&xt_osf_nfnetlink);
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err_out_exit:
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return err;
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}
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static void __exit xt_osf_fini(void)
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{
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struct xt_osf_finger *f;
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int i;
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nfnetlink_subsys_unregister(&xt_osf_nfnetlink);
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xt_unregister_match(&xt_osf_match);
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rcu_read_lock();
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for (i=0; i<ARRAY_SIZE(xt_osf_fingers); ++i) {
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list_for_each_entry_rcu(f, &xt_osf_fingers[i], finger_entry) {
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list_del_rcu(&f->finger_entry);
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kfree_rcu(f, rcu_head);
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}
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}
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rcu_read_unlock();
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rcu_barrier();
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}
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module_init(xt_osf_init);
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module_exit(xt_osf_fini);
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MODULE_LICENSE("GPL");
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MODULE_AUTHOR("Evgeniy Polyakov <zbr@ioremap.net>");
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MODULE_DESCRIPTION("Passive OS fingerprint matching.");
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MODULE_ALIAS("ipt_osf");
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MODULE_ALIAS("ip6t_osf");
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MODULE_ALIAS_NFNL_SUBSYS(NFNL_SUBSYS_OSF);
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