1// SPDX-License-Identifier: GPL-2.0-only
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 = &regs->data[priv->dreg];
25	struct sk_buff *skb = pkt->skb;
26	char os_match[NFT_OSF_MAXGENRELEN];
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		strscpy_pad((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			strscpy(os_match, data.genre, NFT_OSF_MAXGENRELEN);
55
56		strscpy_pad((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	u8 ttl;
67
68	if (!tb[NFTA_OSF_DREG])
69		return -EINVAL;
70
71	if (tb[NFTA_OSF_TTL]) {
72		ttl = nla_get_u8(tb[NFTA_OSF_TTL]);
73		if (ttl > 2)
74			return -EINVAL;
75		priv->ttl = ttl;
76	}
77
78	if (tb[NFTA_OSF_FLAGS]) {
79		flags = ntohl(nla_get_be32(tb[NFTA_OSF_FLAGS]));
80		if (flags != NFT_OSF_F_VERSION)
81			return -EINVAL;
82		priv->flags = flags;
83	}
84
85	return nft_parse_register_store(ctx, tb[NFTA_OSF_DREG], &priv->dreg,
86					NULL, NFT_DATA_VALUE,
87					NFT_OSF_MAXGENRELEN);
88}
89
90static int nft_osf_dump(struct sk_buff *skb,
91			const struct nft_expr *expr, bool reset)
92{
93	const struct nft_osf *priv = nft_expr_priv(expr);
94
95	if (nla_put_u8(skb, NFTA_OSF_TTL, priv->ttl))
96		goto nla_put_failure;
97
98	if (nla_put_u32(skb, NFTA_OSF_FLAGS, ntohl((__force __be32)priv->flags)))
99		goto nla_put_failure;
100
101	if (nft_dump_register(skb, NFTA_OSF_DREG, priv->dreg))
102		goto nla_put_failure;
103
104	return 0;
105
106nla_put_failure:
107	return -1;
108}
109
110static int nft_osf_validate(const struct nft_ctx *ctx,
111			    const struct nft_expr *expr,
112			    const struct nft_data **data)
113{
114	unsigned int hooks;
115
116	switch (ctx->family) {
117	case NFPROTO_IPV4:
118	case NFPROTO_IPV6:
119	case NFPROTO_INET:
120		hooks = (1 << NF_INET_LOCAL_IN) |
121			(1 << NF_INET_PRE_ROUTING) |
122			(1 << NF_INET_FORWARD);
123		break;
124	default:
125		return -EOPNOTSUPP;
126	}
127
128	return nft_chain_validate_hooks(ctx->chain, hooks);
129}
130
131static bool nft_osf_reduce(struct nft_regs_track *track,
132			   const struct nft_expr *expr)
133{
134	struct nft_osf *priv = nft_expr_priv(expr);
135	struct nft_osf *osf;
136
137	if (!nft_reg_track_cmp(track, expr, priv->dreg)) {
138		nft_reg_track_update(track, expr, priv->dreg, NFT_OSF_MAXGENRELEN);
139		return false;
140	}
141
142	osf = nft_expr_priv(track->regs[priv->dreg].selector);
143	if (priv->flags != osf->flags ||
144	    priv->ttl != osf->ttl) {
145		nft_reg_track_update(track, expr, priv->dreg, NFT_OSF_MAXGENRELEN);
146		return false;
147	}
148
149	if (!track->regs[priv->dreg].bitwise)
150		return true;
151
152	return false;
153}
154
155static struct nft_expr_type nft_osf_type;
156static const struct nft_expr_ops nft_osf_op = {
157	.eval		= nft_osf_eval,
158	.size		= NFT_EXPR_SIZE(sizeof(struct nft_osf)),
159	.init		= nft_osf_init,
160	.dump		= nft_osf_dump,
161	.type		= &nft_osf_type,
162	.validate	= nft_osf_validate,
163	.reduce		= nft_osf_reduce,
164};
165
166static struct nft_expr_type nft_osf_type __read_mostly = {
167	.ops		= &nft_osf_op,
168	.name		= "osf",
169	.owner		= THIS_MODULE,
170	.policy		= nft_osf_policy,
171	.maxattr	= NFTA_OSF_MAX,
172};
173
174static int __init nft_osf_module_init(void)
175{
176	return nft_register_expr(&nft_osf_type);
177}
178
179static void __exit nft_osf_module_exit(void)
180{
181	return nft_unregister_expr(&nft_osf_type);
182}
183
184module_init(nft_osf_module_init);
185module_exit(nft_osf_module_exit);
186
187MODULE_LICENSE("GPL");
188MODULE_AUTHOR("Fernando Fernandez <ffmancera@riseup.net>");
189MODULE_ALIAS_NFT_EXPR("osf");
190MODULE_DESCRIPTION("nftables passive OS fingerprint support");
191