netfilter: nf_tables: implement Passive OS fingerprint module in nft_osf

Add basic module functions into nft_osf.[ch] in order to implement OSF
module in nf_tables.

Signed-off-by: Fernando Fernandez Mancera <ffmancera@riseup.net>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

diff --git a/include/uapi/linux/netfilter/nf_tables.h b/include/uapi/linux/netfilter/nf_tables.h
index f466860..382c32d 100644 (file)
--- a/include/uapi/linux/netfilter/nf_tables.h
+++ b/include/uapi/linux/netfilter/nf_tables.h
@@ -1463,6 +1463,13 @@ enum nft_flowtable_hook_attributes {
 };
 #define NFTA_FLOWTABLE_HOOK_MAX        (__NFTA_FLOWTABLE_HOOK_MAX - 1)
 
+enum nft_osf_attributes {
+       NFTA_OSF_UNSPEC,
+       NFTA_OSF_DREG,
+       __NFTA_OSF_MAX,
+};
+#define NFTA_OSF_MAX (__NFTA_OSF_MAX - 1)
+
 /**
  * enum nft_device_attributes - nf_tables device netlink attributes
  *

diff --git a/net/netfilter/Kconfig b/net/netfilter/Kconfig
index 8533343..16fdfb7 100644 (file)
--- a/net/netfilter/Kconfig
+++ b/net/netfilter/Kconfig
@@ -627,6 +627,13 @@ config NFT_SOCKET
          This option allows matching for the presence or absence of a
          corresponding socket and its attributes.
 
+config NFT_OSF
+       tristate "Netfilter nf_tables passive OS fingerprint support"
+       depends on NETFILTER_ADVANCED
+       select NETFILTER_NETLINK_OSF
+       help
+         This option allows matching packets from an specific OS.
+
 if NF_TABLES_NETDEV
 
 config NF_DUP_NETDEV

diff --git a/net/netfilter/Makefile b/net/netfilter/Makefile
index e684f9b..5cbbf69 100644 (file)
--- a/net/netfilter/Makefile
+++ b/net/netfilter/Makefile
@@ -110,6 +110,7 @@ obj-$(CONFIG_NFT_FIB)               += nft_fib.o
 obj-$(CONFIG_NFT_FIB_INET)     += nft_fib_inet.o
 obj-$(CONFIG_NFT_FIB_NETDEV)   += nft_fib_netdev.o
 obj-$(CONFIG_NFT_SOCKET)       += nft_socket.o
+obj-$(CONFIG_NFT_OSF)          += nft_osf.o
 
 # nf_tables netdev
 obj-$(CONFIG_NFT_DUP_NETDEV)   += nft_dup_netdev.o

diff --git a/net/netfilter/nft_osf.c b/net/netfilter/nft_osf.c
new file mode 100644 (file)
index 0000000..bdacc4c
--- /dev/null
+++ b/net/netfilter/nft_osf.c
@@ -0,0 +1,106 @@
+#include <net/ip.h>
+#include <net/tcp.h>
+
+#include <net/netfilter/nf_tables.h>
+#include <linux/netfilter/nf_osf.h>
+
+#define OSF_GENRE_SIZE         32
+
+struct nft_osf {
+       enum nft_registers      dreg:8;
+};
+
+static const struct nla_policy nft_osf_policy[NFTA_OSF_MAX + 1] = {
+       [NFTA_OSF_DREG]         = { .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 = &regs->data[priv->dreg];
+       struct sk_buff *skb = pkt->skb;
+       const struct tcphdr *tcp;
+       struct tcphdr _tcph;
+       const char *os_name;
+
+       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;
+       }
+
+       os_name = nf_osf_find(skb, nf_osf_fingers);
+       if (!os_name)
+               strncpy((char *)dest, "unknown", IFNAMSIZ);
+       else
+               strncpy((char *)dest, os_name, IFNAMSIZ);
+}
+
+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);
+       int err;
+
+       priv->dreg = nft_parse_register(tb[NFTA_OSF_DREG]);
+       err = nft_validate_register_store(ctx, priv->dreg, NULL,
+                                         NFTA_DATA_VALUE, OSF_GENRE_SIZE);
+       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 (nft_dump_register(skb, NFTA_OSF_DREG, priv->dreg))
+               goto nla_put_failure;
+
+       return 0;
+
+nla_put_failure:
+       return -1;
+}
+
+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,
+};
+
+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");