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@xxxxxxxxxxxxx>
---
Compile tested only.
net/netfilter/nf_osf.c | 207 ++++++++++++++++++++++++++-----------------------
1 file changed, 111 insertions(+), 96 deletions(-)
diff --git a/net/netfilter/nf_osf.c b/net/netfilter/nf_osf.c
index 5ba5c7bef2f9..bd7b34dd7d87 100644
--- a/net/netfilter/nf_osf.c
+++ b/net/netfilter/nf_osf.c
@@ -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;
@@ -52,6 +51,104 @@ 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,
@@ -59,15 +156,16 @@ nf_osf_match(const struct sk_buff *skb, u_int8_t family,
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);
@@ -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++;
--
2.11.0
--
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