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// SPDX-License-Identifier: GPL-2.0-only
#include <net/ip.h>
#include <net/tcp.h>
#include <net/netfilter/nf_tables.h>
#include <linux/netfilter/nfnetlink_osf.h>
struct nft_osf {
u8 dreg;
u8 ttl;
u32 flags;
};
static const struct nla_policy nft_osf_policy[NFTA_OSF_MAX + 1] = {
[NFTA_OSF_DREG] = { .type = NLA_U32 },
[NFTA_OSF_TTL] = { .type = NLA_U8 },
[NFTA_OSF_FLAGS] = { .type = NLA_U32 },
};
static void nft_osf_eval(const struct nft_expr *expr, struct nft_regs *regs,
const struct nft_pktinfo *pkt)
{
struct nft_osf *priv = nft_expr_priv(expr);
u32 *dest = ®s->data[priv->dreg];
struct sk_buff *skb = pkt->skb;
char os_match[NFT_OSF_MAXGENRELEN + 1];
const struct tcphdr *tcp;
struct nf_osf_data data;
struct tcphdr _tcph;
if (pkt->tprot != IPPROTO_TCP) {
regs->verdict.code = NFT_BREAK;
return;
}
tcp = skb_header_pointer(skb, ip_hdrlen(skb),
sizeof(struct tcphdr), &_tcph);
if (!tcp) {
regs->verdict.code = NFT_BREAK;
return;
}
if (!tcp->syn) {
regs->verdict.code = NFT_BREAK;
return;
}
if (!nf_osf_find(skb, nf_osf_fingers, priv->ttl, &data)) {
strncpy((char *)dest, "unknown", NFT_OSF_MAXGENRELEN);
} else {
if (priv->flags & NFT_OSF_F_VERSION)
snprintf(os_match, NFT_OSF_MAXGENRELEN, "%s:%s",
data.genre, data.version);
else
strlcpy(os_match, data.genre, NFT_OSF_MAXGENRELEN);
strncpy((char *)dest, os_match, NFT_OSF_MAXGENRELEN);
}
}
static int nft_osf_init(const struct nft_ctx *ctx,
const struct nft_expr *expr,
const struct nlattr * const tb[])
{
struct nft_osf *priv = nft_expr_priv(expr);
u32 flags;
int err;
u8 ttl;
if (!tb[NFTA_OSF_DREG])
return -EINVAL;
if (tb[NFTA_OSF_TTL]) {
ttl = nla_get_u8(tb[NFTA_OSF_TTL]);
if (ttl > 2)
return -EINVAL;
priv->ttl = ttl;
}
if (tb[NFTA_OSF_FLAGS]) {
flags = ntohl(nla_get_be32(tb[NFTA_OSF_FLAGS]));
if (flags != NFT_OSF_F_VERSION)
return -EINVAL;
priv->flags = flags;
}
err = nft_parse_register_store(ctx, tb[NFTA_OSF_DREG], &priv->dreg,
NULL, NFT_DATA_VALUE,
NFT_OSF_MAXGENRELEN);
if (err < 0)
return err;
return 0;
}
static int nft_osf_dump(struct sk_buff *skb, const struct nft_expr *expr)
{
const struct nft_osf *priv = nft_expr_priv(expr);
if (nla_put_u8(skb, NFTA_OSF_TTL, priv->ttl))
goto nla_put_failure;
if (nla_put_be32(skb, NFTA_OSF_FLAGS, ntohl(priv->flags)))
goto nla_put_failure;
if (nft_dump_register(skb, NFTA_OSF_DREG, priv->dreg))
goto nla_put_failure;
return 0;
nla_put_failure:
return -1;
}
static int nft_osf_validate(const struct nft_ctx *ctx,
const struct nft_expr *expr,
const struct nft_data **data)
{
return nft_chain_validate_hooks(ctx->chain, (1 << NF_INET_LOCAL_IN) |
(1 << NF_INET_PRE_ROUTING) |
(1 << NF_INET_FORWARD));
}
static struct nft_expr_type nft_osf_type;
static const struct nft_expr_ops nft_osf_op = {
.eval = nft_osf_eval,
.size = NFT_EXPR_SIZE(sizeof(struct nft_osf)),
.init = nft_osf_init,
.dump = nft_osf_dump,
.type = &nft_osf_type,
.validate = nft_osf_validate,
};
static struct nft_expr_type nft_osf_type __read_mostly = {
.ops = &nft_osf_op,
.name = "osf",
.owner = THIS_MODULE,
.policy = nft_osf_policy,
.maxattr = NFTA_OSF_MAX,
};
static int __init nft_osf_module_init(void)
{
return nft_register_expr(&nft_osf_type);
}
static void __exit nft_osf_module_exit(void)
{
return nft_unregister_expr(&nft_osf_type);
}
module_init(nft_osf_module_init);
module_exit(nft_osf_module_exit);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Fernando Fernandez <ffmancera@riseup.net>");
MODULE_ALIAS_NFT_EXPR("osf");
MODULE_DESCRIPTION("nftables passive OS fingerprint support");
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