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netfilter: nf_osf: add nf_osf_match_one()
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This new function allows us to check if there is TCP syn packet matching
with a given fingerprint that can be reused from the upcoming new
nf_osf_find() function.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
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Pablo Neira Ayuso committed Jul 18, 2018
1 parent f102d66 commit 06ff4aa
Showing 1 changed file with 111 additions and 96 deletions.
207 changes: 111 additions & 96 deletions net/netfilter/nf_osf.c
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Original file line number Diff line number Diff line change
Expand Up @@ -21,15 +21,14 @@
#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)
int ttl_check, unsigned char f_ttl)
{
const struct iphdr *ip = ip_hdr(skb);

if (info->flags & NF_OSF_TTL) {
if (info->ttl == NF_OSF_TTL_TRUE)
if (ttl_check != -1) {
if (ttl_check == NF_OSF_TTL_TRUE)
return ip->ttl == f_ttl;
if (info->ttl == NF_OSF_TTL_NOCHECK)
if (ttl_check == NF_OSF_TTL_NOCHECK)
return 1;
else if (ip->ttl <= f_ttl)
return 1;
Expand All @@ -52,22 +51,121 @@ static inline int nf_osf_ttl(const struct sk_buff *skb,
return ip->ttl == f_ttl;
}

static bool nf_osf_match_one(const struct sk_buff *skb,
const struct nf_osf_user_finger *f,
int ttl_check, u16 totlen, u16 window,
const unsigned char *optp,
unsigned int optsize)
{
unsigned int check_WSS = 0;
int fmatch = FMATCH_WRONG;
int foptsize, optnum;
u16 mss = 0;

if (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 ||
optsize > MAX_IPOPTLEN ||
optsize != foptsize)
return false;

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;
}
}

return fmatch == FMATCH_OK;
}

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;
int fcount = 0, ttl_check;
int fmatch = FMATCH_WRONG;
unsigned int optsize = 0;
const struct tcphdr *tcp;
struct tcphdr _tcph;
u16 window, totlen;
bool df;

tcp = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(struct tcphdr), &_tcph);
Expand All @@ -88,103 +186,20 @@ nf_osf_match(const struct sk_buff *skb, u_int8_t family,
sizeof(struct tcphdr), optsize, opts);
}

ttl_check = (info->flags & NF_OSF_TTL) ? info->ttl : -1;

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)
if (!nf_osf_match_one(skb, f,
ttl_check, totlen, window, optp, optsize))
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;
fmatch = FMATCH_OK;

fcount++;

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