Add basic module functions into nft_osf.[ch] in order to start the
implementation of OSF module in nf_tables.

Signed-off-by: Fernando Fernandez Mancera <ffmanc...@riseup.net>
---
 include/uapi/linux/netfilter/nf_osf.h |   7 ++
 include/uapi/linux/netfilter/xt_osf.h |   6 +-
 net/netfilter/Kconfig                 |   7 ++
 net/netfilter/Makefile                |   1 +
 net/netfilter/nft_osf.c               | 108 ++++++++++++++++++++++++++
 5 files changed, 128 insertions(+), 1 deletion(-)
 create mode 100644 net/netfilter/nft_osf.c

diff --git a/include/uapi/linux/netfilter/nf_osf.h 
b/include/uapi/linux/netfilter/nf_osf.h
index 8f2f2f403183..79882b2f7f8e 100644
--- a/include/uapi/linux/netfilter/nf_osf.h
+++ b/include/uapi/linux/netfilter/nf_osf.h
@@ -16,9 +16,16 @@
 
 #define NF_OSF_TTL_TRUE                        0       /* True ip and 
fingerprint TTL comparison */
 
+/* Check if ip TTL is less than fingerprint one */
+#define NF_OSF_TTL_LESS                        1
+
 /* Do not compare ip and fingerprint TTL at all */
 #define NF_OSF_TTL_NOCHECK             2
 
+#define NF_OSF_FLAGMASK                (NF_OSF_GENRE | \
+                                NF_OSF_TTL | \
+                                NF_OSF_LOG | \
+                                NF_OSF_INVERT)
 /* Wildcard MSS (kind of).
  * It is used to implement a state machine for the different wildcard values
  * of the MSS and window sizes.
diff --git a/include/uapi/linux/netfilter/xt_osf.h 
b/include/uapi/linux/netfilter/xt_osf.h
index 72956eceeb09..2f5d4e6d0434 100644
--- a/include/uapi/linux/netfilter/xt_osf.h
+++ b/include/uapi/linux/netfilter/xt_osf.h
@@ -37,8 +37,12 @@
 
 #define XT_OSF_TTL_TRUE                NF_OSF_TTL_TRUE
 #define XT_OSF_TTL_NOCHECK     NF_OSF_TTL_NOCHECK
+#define XT_OSF_TTL_LESS                NF_OSF_TTL_LESS
 
-#define XT_OSF_TTL_LESS        1       /* Check if ip TTL is less than 
fingerprint one */
+#define XT_OSF_FLAGMASK                (XT_OSF_GENRE | \
+                               XT_OSF_TTL | \
+                               XT_OSF_LOG | \
+                               XT_OSF_INVERT)
 
 #define xt_osf_wc              nf_osf_wc
 #define xt_osf_opt             nf_osf_opt
diff --git a/net/netfilter/Kconfig b/net/netfilter/Kconfig
index dbd7d1fad277..e630aac8a081 100644
--- a/net/netfilter/Kconfig
+++ b/net/netfilter/Kconfig
@@ -631,6 +631,13 @@ 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 fingerprinting support"
+       depends on NETFILTER_ADVANCED && NETFILTER_NETLINK
+       select NF_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 44449389e527..d15bd858ecef 100644
--- a/net/netfilter/Makefile
+++ b/net/netfilter/Makefile
@@ -104,6 +104,7 @@ obj-$(CONFIG_NFT_FIB_INET)  += nft_fib_inet.o
 obj-$(CONFIG_NFT_FIB_NETDEV)   += nft_fib_netdev.o
 obj-$(CONFIG_NF_OSF)           += nf_osf.o
 obj-$(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
index 000000000000..30c503f2bf53
--- /dev/null
+++ b/net/netfilter/nft_osf.c
@@ -0,0 +1,108 @@
+#include <net/netfilter/nf_tables.h>
+#include <linux/netfilter/nf_osf.h>
+
+#define OSF_GENRE_SIZE 32
+
+struct nft_osf {
+       char    genre[OSF_GENRE_SIZE];
+       __u32   flags;
+       __u32   loglevel;
+       __u32   ttl;
+       __u32   len;
+};
+
+/* placeholder function WIP */
+static inline bool match_packet(struct nft_osf *priv, struct sk_buff *skb)
+{
+       return 1;
+}
+
+static const struct nla_policy nft_osf_policy[NFTA_OSF_MAX + 1] = {
+       [NFTA_OSF_GENRE]        = { .type = NLA_STRING, .len = OSF_GENRE_SIZE },
+       [NFTA_OSF_FLAGS]        = { .type = NLA_U32 },
+       [NFTA_OSF_LOGLEVEL]     = { .type = NLA_U32 },
+       [NFTA_OSF_TTL]          = { .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);
+       struct sk_buff *skb = pkt->skb;
+
+       if (!match_packet(priv, skb))
+               regs->verdict.code = NFT_BREAK;
+}
+
+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);
+
+       if (tb[NFTA_OSF_GENRE] == NULL)
+               return -EINVAL;
+       nla_strlcpy(priv->genre, tb[NFTA_OSF_GENRE], OSF_GENRE_SIZE);
+       if (ntohl(nla_get_be32(tb[NFTA_OSF_FLAGS])) & ~NF_OSF_FLAGMASK)
+               return -EINVAL;
+       priv->flags     = ntohl(nla_get_be32(tb[NFTA_OSF_FLAGS]));
+       if (ntohl(nla_get_be32(tb[NFTA_OSF_LOGLEVEL])) >=
+                              NF_OSF_LOGLEVEL_ALL_KNOWN)
+               return -EINVAL;
+       priv->loglevel  = ntohl(nla_get_be32(tb[NFTA_OSF_LOGLEVEL]));
+       if (ntohl(nla_get_be32(tb[NFTA_OSF_TTL])) >= NF_OSF_TTL_NOCHECK)
+               return -EINVAL;
+       priv->ttl       = ntohl(nla_get_be32(tb[NFTA_OSF_TTL]));
+       priv->len = strlen(priv->genre);
+       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_string(skb, NFTA_OSF_GENRE, priv->genre) ||
+           nla_put_be32(skb, NFTA_OSF_FLAGS, htonl(priv->flags)) ||
+           nla_put_be32(skb, NFTA_OSF_LOGLEVEL, htonl(priv->loglevel)) ||
+           nla_put_be32(skb, NFTA_OSF_TTL, htonl(priv->ttl)))
+               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 <ffmanc...@riseup.net>");
+MODULE_ALIAS_NFT_EXPR("osf");
-- 
2.18.0

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