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netfilter: extract Passive OS fingerprint infrastructure from xt_osf 

Add nf_osf_ttl() and nf_osf_match() into nf_osf.c to prepare for
nf_tables support.

Signed-off-by: Fernando Fernandez Mancera <ffmancera@riseup.net>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
This commit is contained in:
Fernando Fernandez Mancera 2018-05-03 14:05:40 +02:00 committed by Pablo Neira Ayuso
parent 3f9c56a581
commit bfb15f2a95
7 changed files with 359 additions and 289 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

27
include/linux/netfilter/nf_osf.h Normal file
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@ -0,0 +1,27 @@
#include <uapi/linux/netfilter/nf_osf.h>
/* Initial window size option state machine: multiple of mss, mtu or
* plain numeric value. Can also be made as plain numeric value which
* is not a multiple of specified value.
*/
enum nf_osf_window_size_options {
OSF_WSS_PLAIN = 0,
OSF_WSS_MSS,
OSF_WSS_MTU,
OSF_WSS_MODULO,
OSF_WSS_MAX,
};
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,
};
bool nf_osf_match(const struct sk_buff *skb, u_int8_t family,
int hooknum, struct net_device *in, struct net_device *out,
const struct nf_osf_info *info, struct net *net,
const struct list_head *nf_osf_fingers);

90
include/uapi/linux/netfilter/nf_osf.h Normal file
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@ -0,0 +1,90 @@
#ifndef _NF_OSF_H
#define _NF_OSF_H
#define MAXGENRELEN 32
#define NF_OSF_GENRE (1 << 0)
#define NF_OSF_TTL (1 << 1)
#define NF_OSF_LOG (1 << 2)
#define NF_OSF_INVERT (1 << 3)
#define NF_OSF_LOGLEVEL_ALL 0 /* log all matched fingerprints */
#define NF_OSF_LOGLEVEL_FIRST 1 /* log only the first matced fingerprint */
#define NF_OSF_LOGLEVEL_ALL_KNOWN 2 /* do not log unknown packets */
#define NF_OSF_TTL_TRUE 0 /* True ip and fingerprint TTL comparison */
/* Do not compare ip and fingerprint TTL at all */
#define NF_OSF_TTL_NOCHECK 2
/* Wildcard MSS (kind of).
* It is used to implement a state machine for the different wildcard values
* of the MSS and window sizes.
*/
struct nf_osf_wc {
__u32 wc;
__u32 val;
};
/* This struct represents IANA options
* http://www.iana.org/assignments/tcp-parameters
*/
struct nf_osf_opt {
__u16 kind, length;
struct nf_osf_wc wc;
};
struct nf_osf_info {
char genre[MAXGENRELEN];
__u32 len;
__u32 flags;
__u32 loglevel;
__u32 ttl;
};
struct nf_osf_user_finger {
struct nf_osf_wc wss;
__u8 ttl, df;
__u16 ss, mss;
__u16 opt_num;
char genre[MAXGENRELEN];
char version[MAXGENRELEN];
char subtype[MAXGENRELEN];
/* MAX_IPOPTLEN is maximum if all options are NOPs or EOLs */
struct nf_osf_opt opt[MAX_IPOPTLEN];
};
struct nf_osf_finger {
struct rcu_head rcu_head;
struct list_head finger_entry;
struct nf_osf_user_finger finger;
};
struct nf_osf_nlmsg {
struct nf_osf_user_finger f;
struct iphdr ip;
struct tcphdr tcp;
};
/* Defines for IANA option kinds */
enum iana_options {
OSFOPT_EOL = 0, /* End of options */
OSFOPT_NOP, /* NOP */
OSFOPT_MSS, /* Maximum segment size */
OSFOPT_WSO, /* Window scale option */
OSFOPT_SACKP, /* SACK permitted */
OSFOPT_SACK, /* SACK */
OSFOPT_ECHO,
OSFOPT_ECHOREPLY,
OSFOPT_TS, /* Timestamp option */
OSFOPT_POCP, /* Partial Order Connection Permitted */
OSFOPT_POSP, /* Partial Order Service Profile */
/* Others are not used in the current OSF */
OSFOPT_EMPTY = 255,
};
#endif /* _NF_OSF_H */

106
include/uapi/linux/netfilter/xt_osf.h
View File

@ -23,101 +23,29 @@
#include <linux/types.h>
#include <linux/ip.h>
#include <linux/tcp.h>
#include <linux/netfilter/nf_osf.h>
#define MAXGENRELEN 32
#define XT_OSF_GENRE NF_OSF_GENRE
#define XT_OSF_INVERT NF_OSF_INVERT
#define XT_OSF_GENRE (1<<0)
#define XT_OSF_TTL (1<<1)
#define XT_OSF_LOG (1<<2)
#define XT_OSF_INVERT (1<<3)
#define XT_OSF_TTL NF_OSF_TTL
#define XT_OSF_LOG NF_OSF_LOG
#define XT_OSF_LOGLEVEL_ALL 0 /* log all matched fingerprints */
#define XT_OSF_LOGLEVEL_FIRST 1 /* log only the first matced fingerprint */
#define XT_OSF_LOGLEVEL_ALL_KNOWN 2 /* do not log unknown packets */
#define XT_OSF_LOGLEVEL_ALL NF_OSF_LOGLEVEL_ALL
#define XT_OSF_LOGLEVEL_FIRST NF_OSF_LOGLEVEL_FIRST
#define XT_OSF_LOGLEVEL_ALL_KNOWN NF_OSF_LOGLEVEL_ALL_KNOWN
#define XT_OSF_TTL_TRUE 0 /* True ip and fingerprint TTL comparison */
#define XT_OSF_TTL_LESS 1 /* Check if ip TTL is less than fingerprint one */
#define XT_OSF_TTL_NOCHECK 2 /* Do not compare ip and fingerprint TTL at all */
#define XT_OSF_TTL_TRUE NF_OSF_TTL_TRUE
#define XT_OSF_TTL_NOCHECK NF_OSF_TTL_NOCHECK
struct xt_osf_info {
char genre[MAXGENRELEN];
__u32 len;
__u32 flags;
__u32 loglevel;
__u32 ttl;
};
#define XT_OSF_TTL_LESS 1 /* Check if ip TTL is less than fingerprint one */
/*
* Wildcard MSS (kind of).
* It is used to implement a state machine for the different wildcard values
* of the MSS and window sizes.
*/
struct xt_osf_wc {
__u32 wc;
__u32 val;
};
/*
* This struct represents IANA options
* http://www.iana.org/assignments/tcp-parameters
*/
struct xt_osf_opt {
__u16 kind, length;
struct xt_osf_wc wc;
};
struct xt_osf_user_finger {
struct xt_osf_wc wss;
__u8 ttl, df;
__u16 ss, mss;
__u16 opt_num;
char genre[MAXGENRELEN];
char version[MAXGENRELEN];
char subtype[MAXGENRELEN];
/* MAX_IPOPTLEN is maximum if all options are NOPs or EOLs */
struct xt_osf_opt opt[MAX_IPOPTLEN];
};
struct xt_osf_nlmsg {
struct xt_osf_user_finger f;
struct iphdr ip;
struct tcphdr tcp;
};
/* Defines for IANA option kinds */
enum iana_options {
OSFOPT_EOL = 0, /* End of options */
OSFOPT_NOP, /* NOP */
OSFOPT_MSS, /* Maximum segment size */
OSFOPT_WSO, /* Window scale option */
OSFOPT_SACKP, /* SACK permitted */
OSFOPT_SACK, /* SACK */
OSFOPT_ECHO,
OSFOPT_ECHOREPLY,
OSFOPT_TS, /* Timestamp option */
OSFOPT_POCP, /* Partial Order Connection Permitted */
OSFOPT_POSP, /* Partial Order Service Profile */
/* Others are not used in the current OSF */
OSFOPT_EMPTY = 255,
};
/*
* Initial window size option state machine: multiple of mss, mtu or
* plain numeric value. Can also be made as plain numeric value which
* is not a multiple of specified value.
*/
enum xt_osf_window_size_options {
OSF_WSS_PLAIN = 0,
OSF_WSS_MSS,
OSF_WSS_MTU,
OSF_WSS_MODULO,
OSF_WSS_MAX,
};
#define xt_osf_wc nf_osf_wc
#define xt_osf_opt nf_osf_opt
#define xt_osf_info nf_osf_info
#define xt_osf_user_finger nf_osf_user_finger
#define xt_osf_finger nf_osf_finger
#define xt_osf_nlmsg nf_osf_nlmsg
/*
* Add/remove fingerprint from the kernel.

4
net/netfilter/Kconfig
View File

@ -444,6 +444,9 @@ config NETFILTER_SYNPROXY
endif # NF_CONNTRACK
config NF_OSF
tristate 'Passive OS fingerprint infrastructure'
config NF_TABLES
select NETFILTER_NETLINK
tristate "Netfilter nf_tables support"
@ -1358,6 +1361,7 @@ config NETFILTER_XT_MATCH_NFACCT
config NETFILTER_XT_MATCH_OSF
tristate '"osf" Passive OS fingerprint match'
depends on NETFILTER_ADVANCED && NETFILTER_NETLINK
select NF_OSF
help
This option selects the Passive OS Fingerprinting match module
that allows to passively match the remote operating system by

1
net/netfilter/Makefile
View File

@ -101,6 +101,7 @@ obj-$(CONFIG_NFT_HASH) += nft_hash.o
obj-$(CONFIG_NFT_FIB) += nft_fib.o
obj-$(CONFIG_NFT_FIB_INET) += nft_fib_inet.o
obj-$(CONFIG_NFT_FIB_NETDEV) += nft_fib_netdev.o
obj-$(CONFIG_NF_OSF) += nf_osf.o
# nf_tables netdev
obj-$(CONFIG_NFT_DUP_NETDEV) += nft_dup_netdev.o

218
net/netfilter/nf_osf.c Normal file
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@ -0,0 +1,218 @@
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/capability.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/nf_osf.h>
static inline int nf_osf_ttl(const struct sk_buff *skb,
const struct nf_osf_info *info,
unsigned char f_ttl)
{
const struct iphdr *ip = ip_hdr(skb);
if (info->flags & NF_OSF_TTL) {
if (info->ttl == NF_OSF_TTL_TRUE)
return ip->ttl == f_ttl;
if (info->ttl == NF_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;
}
bool
nf_osf_match(const struct sk_buff *skb, u_int8_t family,
int hooknum, struct net_device *in, struct net_device *out,
const struct nf_osf_info *info, struct net *net,
const struct list_head *nf_osf_fingers)
{
const unsigned char *optp = NULL, *_optp = NULL;
unsigned int optsize = 0, check_WSS = 0;
int fmatch = FMATCH_WRONG, fcount = 0;
const struct iphdr *ip = ip_hdr(skb);
const struct nf_osf_user_finger *f;
unsigned char opts[MAX_IPOPTLEN];
const struct nf_osf_finger *kf;
u16 window, totlen, mss = 0;
const struct tcphdr *tcp;
struct tcphdr _tcph;
bool df;
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);
}
list_for_each_entry_rcu(kf, &nf_osf_fingers[df], finger_entry) {
int foptsize, optnum;
f = &kf->finger;
if (!(info->flags & NF_OSF_LOG) && strcmp(info->genre, f->genre))
continue;
optp = _optp;
fmatch = FMATCH_WRONG;
if (totlen != f->ss || !nf_osf_ttl(skb, info, f->ttl))
continue;
/*
* 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;
fmatch = FMATCH_OK;
switch (*optp) {
case OSFOPT_MSS:
mss = optp[3];
mss <<= 8;
mss |= optp[2];
mss = ntohs((__force __be16)mss);
break;
case OSFOPT_TS:
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 & NF_OSF_LOG)
nf_log_packet(net, family, hooknum, skb,
in, 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 & NF_OSF_LOG) &&
info->loglevel == NF_OSF_LOGLEVEL_FIRST)
break;
}
if (!fcount && (info->flags & NF_OSF_LOG))
nf_log_packet(net, family, hooknum, skb, in, 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;
}
EXPORT_SYMBOL_GPL(nf_osf_match);
MODULE_LICENSE("GPL");

202
net/netfilter/xt_osf.c
View File

@ -37,21 +37,6 @@
#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.
@ -164,200 +149,17 @@ static const struct nfnetlink_subsystem xt_osf_nfnetlink = {
.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;
struct net *net = xt_net(p);
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);
}
list_for_each_entry_rcu(kf, &xt_osf_fingers[df], finger_entry) {
int foptsize, optnum;
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))
continue;
/*
* 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;
fmatch = FMATCH_OK;
switch (*optp) {
case OSFOPT_MSS:
mss = optp[3];
mss <<= 8;
mss |= optp[2];
mss = ntohs((__force __be16)mss);
break;
case OSFOPT_TS:
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(net, xt_family(p), xt_hooknum(p), skb,
xt_in(p), xt_out(p), 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;
}
if (!fcount && (info->flags & XT_OSF_LOG))
nf_log_packet(net, xt_family(p), xt_hooknum(p), skb, xt_in(p),
xt_out(p), 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;
return nf_osf_match(skb, xt_family(p), xt_hooknum(p), xt_in(p),
xt_out(p), info, net, xt_osf_fingers);
}
static struct xt_match xt_osf_match = {