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netfilter: nf_osf: add struct nf_osf_hdr_ctx
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Wrap context that allow us to guess the OS into a structure.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
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Pablo Neira Ayuso committed Jul 18, 2018
1 parent 06ff4aa commit 31a9c29
Showing 1 changed file with 62 additions and 43 deletions.
105 changes: 62 additions & 43 deletions net/netfilter/nf_osf.c
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Original file line number Diff line number Diff line change
Expand Up @@ -51,18 +51,25 @@ static inline int nf_osf_ttl(const struct sk_buff *skb,
return ip->ttl == f_ttl;
}

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, u16 totlen, u16 window,
const unsigned char *optp,
unsigned int optsize)
int ttl_check,
struct nf_osf_hdr_ctx *ctx)
{
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))
if (ctx->totlen != f->ss || !nf_osf_ttl(skb, ttl_check, f->ttl))
return false;

/*
Expand All @@ -78,32 +85,32 @@ static bool nf_osf_match_one(const struct sk_buff *skb,
foptsize += f->opt[optnum].length;

if (foptsize > MAX_IPOPTLEN ||
optsize > MAX_IPOPTLEN ||
optsize != foptsize)
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 == (*optp)) {
if (f->opt[optnum].kind == *ctx->optp) {
__u32 len = f->opt[optnum].length;
const __u8 *optend = optp + len;
const __u8 *optend = ctx->optp + len;

fmatch = FMATCH_OK;

switch (*optp) {
switch (*ctx->optp) {
case OSFOPT_MSS:
mss = optp[3];
mss = ctx->optp[3];
mss <<= 8;
mss |= optp[2];
mss |= ctx->optp[2];

mss = ntohs((__force __be16)mss);
break;
case OSFOPT_TS:
break;
}

optp = optend;
ctx->optp = optend;
} else
fmatch = FMATCH_OPT_WRONG;

Expand All @@ -116,7 +123,7 @@ static bool nf_osf_match_one(const struct sk_buff *skb,

switch (check_WSS) {
case OSF_WSS_PLAIN:
if (f->wss.val == 0 || window == f->wss.val)
if (f->wss.val == 0 || ctx->window == f->wss.val)
fmatch = FMATCH_OK;
break;
case OSF_WSS_MSS:
Expand All @@ -128,19 +135,19 @@ static bool nf_osf_match_one(const struct sk_buff *skb,
*/
#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)
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 (window == f->wss.val * (mss + 40) ||
window == f->wss.val * (SMART_MSS_1 + 40) ||
window == f->wss.val * (SMART_MSS_2 + 40))
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 ((window % f->wss.val) == 0)
if ((ctx->window % f->wss.val) == 0)
fmatch = FMATCH_OK;
break;
}
Expand All @@ -149,54 +156,66 @@ static bool nf_osf_match_one(const struct sk_buff *skb,
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)
{
const struct tcphdr *tcp;
struct tcphdr _tcph;

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);
}

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 unsigned char *optp = NULL, *_optp = NULL;
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;
unsigned int optsize = 0;
struct nf_osf_hdr_ctx ctx;
const struct tcphdr *tcp;
struct tcphdr _tcph;
u16 window, totlen;
bool df;

tcp = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(struct tcphdr), &_tcph);
if (!tcp)
return false;
memset(&ctx, 0, sizeof(ctx));

if (!tcp->syn)
tcp = nf_osf_hdr_ctx_init(&ctx, skb, ip, opts);
if (!tcp)
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);
}

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

list_for_each_entry_rcu(kf, &nf_osf_fingers[df], finger_entry) {
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, totlen, window, optp, optsize))
if (!nf_osf_match_one(skb, f, ttl_check, &ctx))
continue;

fmatch = FMATCH_OK;
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