// SPDX-License-Identifier: GPL-2.0-only
#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/nfnetlink_osf.h>
/*
* Indexed by dont-fragment bit.
* It is the only constant value in the fingerprint.
*/
struct list_head nf_osf_fingers[2];
EXPORT_SYMBOL_GPL(nf_osf_fingers);
static inline int nf_osf_ttl(const struct sk_buff *skb,
int ttl_check, unsigned char f_ttl)
{
struct in_device *in_dev = __in_dev_get_rcu(skb->dev);
const struct iphdr *ip = ip_hdr(skb);
const struct in_ifaddr *ifa;
int ret = 0;
if (ttl_check == NF_OSF_TTL_TRUE)
return ip->ttl == f_ttl;
if (ttl_check == NF_OSF_TTL_NOCHECK)
return 1;
else if (ip->ttl <= f_ttl)
return 1;
in_dev_for_each_ifa_rcu(ifa, in_dev) {
if (inet_ifa_match(ip->saddr, ifa)) {
ret = (ip->ttl == f_ttl);
break;
}
}
return ret;
}
struct nf_osf_hdr_ctx {
bool df;
u16 window;
u16 totlen;
const unsigned char *optp;
unsigned int optsize;
};
static bool nf_osf_match_one(const struct sk_buff *skb,
const struct nf_osf_user_finger *f,
int ttl_check,
struct nf_osf_hdr_ctx *ctx)
{
const __u8 *optpinit = ctx->optp;
unsigned int check_WSS = 0;
int fmatch = FMATCH_WRONG;
int foptsize, optnum;
u16 mss = 0;
if (ctx->totlen != f->ss || !nf_osf_ttl(skb, ttl_check, f->ttl))
return false;
/*
* Should not happen if userspace parser was written correctly.
*/
if (f->wss.wc >= OSF_WSS_MAX)
return false;
/* Check options */
foptsize = 0;
for (optnum = 0; optnum < f->opt_num; ++optnum)
foptsize += f->opt[optnum].length;
if (foptsize > MAX_IPOPTLEN ||
ctx->optsize > MAX_IPOPTLEN ||
ctx->optsize != foptsize)
return false;
check_WSS = f->wss.wc;
for (optnum = 0; optnum < f->opt_num; ++optnum) {
if (f->opt[optnum].kind == *ctx->optp) {
__u32 len = f->opt[optnum].length;
const __u8 *optend = ctx->optp + len;
fmatch = FMATCH_OK;
switch (*ctx->optp) {
case OSFOPT_MSS:
mss = ctx->optp[3];
mss <<= 8;
mss |= ctx->optp[2];
mss = ntohs((__force __be16)mss);
break;
case OSFOPT_TS:
break;
}
ctx->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 || ctx->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 (ctx->window == f->wss.val * mss ||
ctx->window == f->wss.val * SMART_MSS_1 ||
ctx->window == f->wss.val * SMART_MSS_2)
fmatch = FMATCH_OK;
break;
case OSF_WSS_MTU:
if (ctx->window == f->wss.val * (mss + 40) ||
ctx->window == f->wss.val * (SMART_MSS_1 + 40) ||
ctx->window == f->wss.val * (SMART_MSS_2 + 40))
fmatch = FMATCH_OK;
break;
case OSF_WSS_MODULO:
if ((ctx->window % f->wss.val) == 0)
fmatch = FMATCH_OK;
break;
}
}
if (fmatch != FMATCH_OK)
ctx->optp = optpinit;
return fmatch == FMATCH_OK;
}
static const struct tcphdr *nf_osf_hdr_ctx_init(struct nf_osf_hdr_ctx *ctx,
const struct sk_buff *skb,
const struct iphdr *ip,
unsigned char *opts,
struct tcphdr *_tcph)
{
const struct tcphdr *tcp;
tcp = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(struct tcphdr), _tcph);
if (!tcp)
return NULL;
if (!tcp->syn)
return NULL;
ctx->totlen = ntohs(ip->tot_len);
ctx->df = ntohs(ip->frag_off) & IP_DF;
ctx->window = ntohs(tcp->window);
if (tcp->doff * 4 > sizeof(struct tcphdr)) {
ctx->optsize = tcp->doff * 4 - sizeof(struct tcphdr);
ctx->optp = skb_header_pointer(skb, ip_hdrlen(skb) +
sizeof(struct tcphdr), ctx->optsize, opts);
if (!ctx->optp)
return NULL;
}
return tcp;
}
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 struct iphdr *ip = ip_hdr(skb);
const struct nf_osf_user_finger *f;
unsigned char opts[MAX_IPOPTLEN];
const struct nf_osf_finger *kf;
int fcount = 0, ttl_check;
int fmatch = FMATCH_WRONG;
struct nf_osf_hdr_ctx ctx;
const struct tcphdr *tcp;
struct tcphdr _tcph;
memset(&ctx, 0, sizeof(ctx));
tcp = nf_osf_hdr_ctx_init(&ctx, skb, ip, opts, &_tcph);
if (!tcp)
return false;
ttl_check = (info->flags & NF_OSF_TTL) ? info->ttl : 0;
list_for_each_entry_rcu(kf, &nf_osf_fingers[ctx.df], finger_entry) {
f = &kf->finger;
if (!(info->flags & NF_OSF_LOG) && strcmp(info->genre, f->genre))
continue;
if (!nf_osf_match_one(skb, f, ttl_check, &ctx))
continue;
fmatch = FMATCH_OK;
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);
bool nf_osf_find(const struct sk_buff *skb,
const struct list_head *nf_osf_fingers,
const int ttl_check, struct nf_osf_data *data)
{
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;
struct nf_osf_hdr_ctx ctx;
const struct tcphdr *tcp;
struct tcphdr _tcph;
bool found = false;
memset(&ctx, 0, sizeof(ctx));
tcp = nf_osf_hdr_ctx_init(&ctx, skb, ip, opts, &_tcph);
if (!tcp)
return false;
list_for_each_entry_rcu(kf, &nf_osf_fingers[ctx.df], finger_entry) {
f = &kf->finger;
if (!nf_osf_match_one(skb, f, ttl_check, &ctx))
continue;
data->genre = f->genre;
data->version = f->version;
found = true;
break;
}
return found;
}
EXPORT_SYMBOL_GPL(nf_osf_find);
static const struct nla_policy nfnl_osf_policy[OSF_ATTR_MAX + 1] = {
[OSF_ATTR_FINGER] = { .len = sizeof(struct nf_osf_user_finger) },
};
static int nfnl_osf_add_callback(struct sk_buff *skb,
const struct nfnl_info *info,
const struct nlattr * const osf_attrs[])
{
struct nf_osf_user_finger *f;
struct nf_osf_finger *kf = NULL, *sf;
int err = 0;
if (!capable(CAP_NET_ADMIN))
return -EPERM;
if (!osf_attrs[OSF_ATTR_FINGER])
return -EINVAL;
if (!(info->nlh->nlmsg_flags & NLM_F_CREATE))
return -EINVAL;
f = nla_data(osf_attrs[OSF_ATTR_FINGER]);
if (f->opt_num > ARRAY_SIZE(f->opt))
return -EINVAL;
if (!memchr(f->genre, 0, MAXGENRELEN) ||
!memchr(f->subtype, 0, MAXGENRELEN) ||
!memchr(f->version, 0, MAXGENRELEN))
return -EINVAL;
kf = kmalloc(sizeof(struct nf_osf_finger), GFP_KERNEL);
if (!kf)
return -ENOMEM;
memcpy(&kf->finger, f, sizeof(struct nf_osf_user_finger));
list_for_each_entry(sf, &nf_osf_fingers[!!f->df], finger_entry) {
if (memcmp(&sf->finger, f, sizeof(struct nf_osf_user_finger)))
continue;
kfree(kf);
kf = NULL;
if (info->nlh->nlmsg_flags & NLM_F_EXCL)
err = -EEXIST;
break;
}
/*
* We are protected by nfnl mutex.
*/
if (kf)
list_add_tail_rcu(&kf->finger_entry, &nf_osf_fingers[!!f->df]);
return err;
}
static int nfnl_osf_remove_callback(struct sk_buff *skb,
const struct nfnl_info *info,
const struct nlattr * const osf_attrs[])
{
struct nf_osf_user_finger *f;
struct nf_osf_finger *sf;
int err = -ENOENT;
if (!capable(CAP_NET_ADMIN))
return -EPERM;
if (!osf_attrs[OSF_ATTR_FINGER])
return -EINVAL;
f = nla_data(osf_attrs[OSF_ATTR_FINGER]);
list_for_each_entry(sf, &nf_osf_fingers[!!f->df], finger_entry) {
if (memcmp(&sf->finger, f, sizeof(struct nf_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 nfnl_osf_callbacks[OSF_MSG_MAX] = {
[OSF_MSG_ADD] = {
.call = nfnl_osf_add_callback,
.type = NFNL_CB_MUTEX,
.attr_count = OSF_ATTR_MAX,
.policy = nfnl_osf_policy,
},
[OSF_MSG_REMOVE] = {
.call = nfnl_osf_remove_callback,
.type = NFNL_CB_MUTEX,
.attr_count = OSF_ATTR_MAX,
.policy = nfnl_osf_policy,
},
};
static const struct nfnetlink_subsystem nfnl_osf_subsys = {
.name = "osf",
.subsys_id = NFNL_SUBSYS_OSF,
.cb_count = OSF_MSG_MAX,
.cb = nfnl_osf_callbacks,
};
static int __init nfnl_osf_init(void)
{
int err = -EINVAL;
int i;
for (i = 0; i < ARRAY_SIZE(nf_osf_fingers); ++i)
INIT_LIST_HEAD(&nf_osf_fingers[i]);
err = nfnetlink_subsys_register(&nfnl_osf_subsys);
if (err < 0) {
pr_err("Failed to register OSF nsfnetlink helper (%d)\n", err);
goto err_out_exit;
}
return 0;
err_out_exit:
return err;
}
static void __exit nfnl_osf_fini(void)
{
struct nf_osf_finger *f;
int i;
nfnetlink_subsys_unregister(&nfnl_osf_subsys);
rcu_read_lock();
for (i = 0; i < ARRAY_SIZE(nf_osf_fingers); ++i) {
list_for_each_entry_rcu(f, &nf_osf_fingers[i], finger_entry) {
list_del_rcu(&f->finger_entry);
kfree_rcu(f, rcu_head);
}
}
rcu_read_unlock();
rcu_barrier();
}
module_init(nfnl_osf_init);
module_exit(nfnl_osf_fini);
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("Passive OS fingerprint matching");
MODULE_ALIAS_NFNL_SUBSYS(NFNL_SUBSYS_OSF);
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