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, offset: ip_hdrlen(skb),
37 len: sizeof(struct tcphdr), buffer: &_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, ttl_check: priv->ttl, data: &data)) {
48 strscpy_pad(dest: (char *)dest, src: "unknown", NFT_OSF_MAXGENRELEN);
49 } else {
50 if (priv->flags & NFT_OSF_F_VERSION)
51 snprintf(buf: os_match, NFT_OSF_MAXGENRELEN, fmt: "%s:%s",
52 data.genre, data.version);
53 else
54 strscpy(p: os_match, q: data.genre, NFT_OSF_MAXGENRELEN);
55
56 strscpy_pad(dest: (char *)dest, src: 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(nla: 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, attr: tb[NFTA_OSF_DREG], dreg: &priv->dreg,
87 NULL, type: 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,
96 const struct nft_expr *expr, bool reset)
97{
98 const struct nft_osf *priv = nft_expr_priv(expr);
99
100 if (nla_put_u8(skb, attrtype: NFTA_OSF_TTL, value: priv->ttl))
101 goto nla_put_failure;
102
103 if (nla_put_u32(skb, attrtype: NFTA_OSF_FLAGS, ntohl((__force __be32)priv->flags)))
104 goto nla_put_failure;
105
106 if (nft_dump_register(skb, attr: NFTA_OSF_DREG, reg: priv->dreg))
107 goto nla_put_failure;
108
109 return 0;
110
111nla_put_failure:
112 return -1;
113}
114
115static int nft_osf_validate(const struct nft_ctx *ctx,
116 const struct nft_expr *expr,
117 const struct nft_data **data)
118{
119 unsigned int hooks;
120
121 switch (ctx->family) {
122 case NFPROTO_IPV4:
123 case NFPROTO_IPV6:
124 case NFPROTO_INET:
125 hooks = (1 << NF_INET_LOCAL_IN) |
126 (1 << NF_INET_PRE_ROUTING) |
127 (1 << NF_INET_FORWARD);
128 break;
129 default:
130 return -EOPNOTSUPP;
131 }
132
133 return nft_chain_validate_hooks(chain: ctx->chain, hook_flags: hooks);
134}
135
136static bool nft_osf_reduce(struct nft_regs_track *track,
137 const struct nft_expr *expr)
138{
139 struct nft_osf *priv = nft_expr_priv(expr);
140 struct nft_osf *osf;
141
142 if (!nft_reg_track_cmp(track, expr, dreg: priv->dreg)) {
143 nft_reg_track_update(track, expr, dreg: priv->dreg, NFT_OSF_MAXGENRELEN);
144 return false;
145 }
146
147 osf = nft_expr_priv(expr: track->regs[priv->dreg].selector);
148 if (priv->flags != osf->flags ||
149 priv->ttl != osf->ttl) {
150 nft_reg_track_update(track, expr, dreg: priv->dreg, NFT_OSF_MAXGENRELEN);
151 return false;
152 }
153
154 if (!track->regs[priv->dreg].bitwise)
155 return true;
156
157 return false;
158}
159
160static struct nft_expr_type nft_osf_type;
161static const struct nft_expr_ops nft_osf_op = {
162 .eval = nft_osf_eval,
163 .size = NFT_EXPR_SIZE(sizeof(struct nft_osf)),
164 .init = nft_osf_init,
165 .dump = nft_osf_dump,
166 .type = &nft_osf_type,
167 .validate = nft_osf_validate,
168 .reduce = nft_osf_reduce,
169};
170
171static struct nft_expr_type nft_osf_type __read_mostly = {
172 .ops = &nft_osf_op,
173 .name = "osf",
174 .owner = THIS_MODULE,
175 .policy = nft_osf_policy,
176 .maxattr = NFTA_OSF_MAX,
177};
178
179static int __init nft_osf_module_init(void)
180{
181 return nft_register_expr(&nft_osf_type);
182}
183
184static void __exit nft_osf_module_exit(void)
185{
186 return nft_unregister_expr(&nft_osf_type);
187}
188
189module_init(nft_osf_module_init);
190module_exit(nft_osf_module_exit);
191
192MODULE_LICENSE("GPL");
193MODULE_AUTHOR("Fernando Fernandez <ffmancera@riseup.net>");
194MODULE_ALIAS_NFT_EXPR("osf");
195MODULE_DESCRIPTION("nftables passive OS fingerprint support");
196

source code of linux/net/netfilter/nft_osf.c