1
2#include <net/ip.h>
3#include <net/tcp.h>
4
5#include <net/netfilter/nf_tables.h>
6#include <linux/netfilter/nfnetlink_osf.h>
7
8struct nft_osf {
9 u8 dreg;
10 u8 ttl;
11 u32 flags;
12};
13
14static const struct nla_policy nft_osf_policy[NFTA_OSF_MAX + 1] = {
15 [NFTA_OSF_DREG] = { .type = NLA_U32 },
16 [NFTA_OSF_TTL] = { .type = NLA_U8 },
17 [NFTA_OSF_FLAGS] = { .type = NLA_U32 },
18};
19
20static void nft_osf_eval(const struct nft_expr *expr, struct nft_regs *regs,
21 const struct nft_pktinfo *pkt)
22{
23 struct nft_osf *priv = nft_expr_priv(expr);
24 u32 *dest = ®s->data[priv->dreg];
25 struct sk_buff *skb = pkt->skb;
26 char os_match[NFT_OSF_MAXGENRELEN + 1];
27 const struct tcphdr *tcp;
28 struct nf_osf_data data;
29 struct tcphdr _tcph;
30
31 if (pkt->tprot != IPPROTO_TCP) {
32 regs->verdict.code = NFT_BREAK;
33 return;
34 }
35
36 tcp = skb_header_pointer(skb, ip_hdrlen(skb),
37 sizeof(struct tcphdr), &_tcph);
38 if (!tcp) {
39 regs->verdict.code = NFT_BREAK;
40 return;
41 }
42 if (!tcp->syn) {
43 regs->verdict.code = NFT_BREAK;
44 return;
45 }
46
47 if (!nf_osf_find(skb, nf_osf_fingers, priv->ttl, &data)) {
48 strncpy((char *)dest, "unknown", NFT_OSF_MAXGENRELEN);
49 } else {
50 if (priv->flags & NFT_OSF_F_VERSION)
51 snprintf(os_match, NFT_OSF_MAXGENRELEN, "%s:%s",
52 data.genre, data.version);
53 else
54 strlcpy(os_match, data.genre, NFT_OSF_MAXGENRELEN);
55
56 strncpy((char *)dest, os_match, NFT_OSF_MAXGENRELEN);
57 }
58}
59
60static int nft_osf_init(const struct nft_ctx *ctx,
61 const struct nft_expr *expr,
62 const struct nlattr * const tb[])
63{
64 struct nft_osf *priv = nft_expr_priv(expr);
65 u32 flags;
66 int err;
67 u8 ttl;
68
69 if (!tb[NFTA_OSF_DREG])
70 return -EINVAL;
71
72 if (tb[NFTA_OSF_TTL]) {
73 ttl = nla_get_u8(tb[NFTA_OSF_TTL]);
74 if (ttl > 2)
75 return -EINVAL;
76 priv->ttl = ttl;
77 }
78
79 if (tb[NFTA_OSF_FLAGS]) {
80 flags = ntohl(nla_get_be32(tb[NFTA_OSF_FLAGS]));
81 if (flags != NFT_OSF_F_VERSION)
82 return -EINVAL;
83 priv->flags = flags;
84 }
85
86 err = nft_parse_register_store(ctx, tb[NFTA_OSF_DREG], &priv->dreg,
87 NULL, NFT_DATA_VALUE,
88 NFT_OSF_MAXGENRELEN);
89 if (err < 0)
90 return err;
91
92 return 0;
93}
94
95static int nft_osf_dump(struct sk_buff *skb, const struct nft_expr *expr)
96{
97 const struct nft_osf *priv = nft_expr_priv(expr);
98
99 if (nla_put_u8(skb, NFTA_OSF_TTL, priv->ttl))
100 goto nla_put_failure;
101
102 if (nla_put_be32(skb, NFTA_OSF_FLAGS, ntohl(priv->flags)))
103 goto nla_put_failure;
104
105 if (nft_dump_register(skb, NFTA_OSF_DREG, priv->dreg))
106 goto nla_put_failure;
107
108 return 0;
109
110nla_put_failure:
111 return -1;
112}
113
114static int nft_osf_validate(const struct nft_ctx *ctx,
115 const struct nft_expr *expr,
116 const struct nft_data **data)
117{
118 return nft_chain_validate_hooks(ctx->chain, (1 << NF_INET_LOCAL_IN) |
119 (1 << NF_INET_PRE_ROUTING) |
120 (1 << NF_INET_FORWARD));
121}
122
123static struct nft_expr_type nft_osf_type;
124static const struct nft_expr_ops nft_osf_op = {
125 .eval = nft_osf_eval,
126 .size = NFT_EXPR_SIZE(sizeof(struct nft_osf)),
127 .init = nft_osf_init,
128 .dump = nft_osf_dump,
129 .type = &nft_osf_type,
130 .validate = nft_osf_validate,
131};
132
133static struct nft_expr_type nft_osf_type __read_mostly = {
134 .ops = &nft_osf_op,
135 .name = "osf",
136 .owner = THIS_MODULE,
137 .policy = nft_osf_policy,
138 .maxattr = NFTA_OSF_MAX,
139};
140
141static int __init nft_osf_module_init(void)
142{
143 return nft_register_expr(&nft_osf_type);
144}
145
146static void __exit nft_osf_module_exit(void)
147{
148 return nft_unregister_expr(&nft_osf_type);
149}
150
151module_init(nft_osf_module_init);
152module_exit(nft_osf_module_exit);
153
154MODULE_LICENSE("GPL");
155MODULE_AUTHOR("Fernando Fernandez <ffmancera@riseup.net>");
156MODULE_ALIAS_NFT_EXPR("osf");
157MODULE_DESCRIPTION("nftables passive OS fingerprint support");
158
