net/netfilter/nft_osf.c

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