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 + 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");