[1/2,WIP,nf-next] netfilter: implement Passive OS fingerprint module in nft_osf

Message ID 20180712103414.2501-1-ffmancera@riseup.net
State RFC
Delegated to: Pablo Neira
Headers show
Series
  • [1/2,WIP,nf-next] netfilter: implement Passive OS fingerprint module in nft_osf
Related show

Commit Message

Fernando Fernandez Mancera July 12, 2018, 10:34 a.m.
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 <ffmancera@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

Comments

Florian Westphal July 12, 2018, 10:53 a.m. | #1
Fernando Fernandez Mancera <ffmancera@riseup.net> wrote:
> Add basic module functions into nft_osf.[ch] in order to start the
> implementation of OSF module in nf_tables.
> 
> +struct nft_osf {
> +	char	genre[OSF_GENRE_SIZE];
> +	__u32	flags;
> +	__u32	loglevel;
> +	__u32	ttl;
> +	__u32	len;
> +};

48 bytes is quite a lot.  Can this be compressed further?

e.g. len appears to be useless, and flags/loglevel/ttl
can probably be u8 or u16.

> +static const struct nla_policy nft_osf_policy[NFTA_OSF_MAX + 1] = {
> +	[NFTA_OSF_GENRE]	= { .type = NLA_STRING, .len = OSF_GENRE_SIZE },

This allows strlen() of OSF_GENRE_SIZE.

> +	[NFTA_OSF_FLAGS]	= { .type = NLA_U32 },
> +	[NFTA_OSF_LOGLEVEL]	= { .type = NLA_U32 },
> +	[NFTA_OSF_TTL]		= { .type = NLA_U32 },
> +};

This looks ok.

> +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);

This then copies OSF_GENRE_SIZE - 1 (for \0).

So its either .len = OSF_GENRE_SIZE - 1,
or genre[OSF_GENRE_SIZE+1], or char *genre + nla_strdup().

> +	priv->len = strlen(priv->genre);

I don't understand need for this.
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Fernando Fernandez Mancera July 12, 2018, 11:26 a.m. | #2
On 07/12/2018 12:53 PM, Florian Westphal wrote:
> Fernando Fernandez Mancera <ffmancera@riseup.net> wrote:
>> Add basic module functions into nft_osf.[ch] in order to start the
>> implementation of OSF module in nf_tables.
>>
>> +struct nft_osf {
>> +	char	genre[OSF_GENRE_SIZE];
>> +	__u32	flags;
>> +	__u32	loglevel;
>> +	__u32	ttl;
>> +	__u32	len;
>> +};
> 
> 48 bytes is quite a lot.  Can this be compressed further?
> 
> e.g. len appears to be useless, and flags/loglevel/ttl
> can probably be u8 or u16.
> 

Agree, u8 should be enough for flags/loglevel/ttl.

>> +static const struct nla_policy nft_osf_policy[NFTA_OSF_MAX + 1] = {
>> +	[NFTA_OSF_GENRE]	= { .type = NLA_STRING, .len = OSF_GENRE_SIZE },
> 
> This allows strlen() of OSF_GENRE_SIZE.
> 
>> +	[NFTA_OSF_FLAGS]	= { .type = NLA_U32 },
>> +	[NFTA_OSF_LOGLEVEL]	= { .type = NLA_U32 },
>> +	[NFTA_OSF_TTL]		= { .type = NLA_U32 },
>> +};
> 
> This looks ok.
> 
>> +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);
> 
> This then copies OSF_GENRE_SIZE - 1 (for \0).
> 
> So its either .len = OSF_GENRE_SIZE - 1,
> or genre[OSF_GENRE_SIZE+1], or char *genre + nla_strdup().
> 
>> +	priv->len = strlen(priv->genre);
> 
> I don't understand need for this.

Yes, I am thinking on getting "len" out.

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kbuild test robot July 12, 2018, 11:14 p.m. | #3
Hi Fernando,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on nf-next/master]

url:    https://github.com/0day-ci/linux/commits/Fernando-Fernandez-Mancera/netfilter-implement-Passive-OS-fingerprint-module-in-nft_osf/20180712-203655
base:   https://git.kernel.org/pub/scm/linux/kernel/git/pablo/nf-next.git master
config: ia64-allmodconfig (attached as .config)
compiler: ia64-linux-gcc (GCC) 8.1.0
reproduce:
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        GCC_VERSION=8.1.0 make.cross ARCH=ia64 

Note: the linux-review/Fernando-Fernandez-Mancera/netfilter-implement-Passive-OS-fingerprint-module-in-nft_osf/20180712-203655 HEAD da6169296e9d1fd467a0717ebcdd42305488927d builds fine.
      It only hurts bisectibility.

All errors (new ones prefixed by >>):

   In file included from include/linux/netfilter/nf_osf.h:1,
                    from net/netfilter/nft_osf.c:2:
>> include/uapi/linux/netfilter/nf_osf.h:66:24: error: 'MAX_IPOPTLEN' undeclared here (not in a function); did you mean 'MAY_OPEN'?
     struct nf_osf_opt opt[MAX_IPOPTLEN];
                           ^~~~~~~~~~~~
                           MAY_OPEN
>> include/uapi/linux/netfilter/nf_osf.h:71:17: error: field 'ip' has incomplete type
     struct iphdr   ip;
                    ^~
>> include/uapi/linux/netfilter/nf_osf.h:72:18: error: field 'tcp' has incomplete type
     struct tcphdr   tcp;
                     ^~~
>> net/netfilter/nft_osf.c:20:47: error: 'NFTA_OSF_MAX' undeclared here (not in a function); did you mean 'NFTA_OBJ_MAX'?
    static const struct nla_policy nft_osf_policy[NFTA_OSF_MAX + 1] = {
                                                  ^~~~~~~~~~~~
                                                  NFTA_OBJ_MAX
>> net/netfilter/nft_osf.c:21:3: error: 'NFTA_OSF_GENRE' undeclared here (not in a function); did you mean 'NF_OSF_GENRE'?
     [NFTA_OSF_GENRE] = { .type = NLA_STRING, .len = OSF_GENRE_SIZE },
      ^~~~~~~~~~~~~~
      NF_OSF_GENRE
>> net/netfilter/nft_osf.c:21:3: error: array index in initializer not of integer type
   net/netfilter/nft_osf.c:21:3: note: (near initialization for 'nft_osf_policy')
>> net/netfilter/nft_osf.c:21:23: error: field name not in record or union initializer
     [NFTA_OSF_GENRE] = { .type = NLA_STRING, .len = OSF_GENRE_SIZE },
                          ^
   net/netfilter/nft_osf.c:21:23: note: (near initialization for 'nft_osf_policy')
   net/netfilter/nft_osf.c:21:43: error: field name not in record or union initializer
     [NFTA_OSF_GENRE] = { .type = NLA_STRING, .len = OSF_GENRE_SIZE },
                                              ^
   net/netfilter/nft_osf.c:21:43: note: (near initialization for 'nft_osf_policy')
>> net/netfilter/nft_osf.c:22:3: error: 'NFTA_OSF_FLAGS' undeclared here (not in a function); did you mean 'NFTA_FIB_FLAGS'?
     [NFTA_OSF_FLAGS] = { .type = NLA_U32 },
      ^~~~~~~~~~~~~~
      NFTA_FIB_FLAGS
   net/netfilter/nft_osf.c:22:3: error: array index in initializer not of integer type
   net/netfilter/nft_osf.c:22:3: note: (near initialization for 'nft_osf_policy')
   net/netfilter/nft_osf.c:22:23: error: field name not in record or union initializer
     [NFTA_OSF_FLAGS] = { .type = NLA_U32 },
                          ^
   net/netfilter/nft_osf.c:22:23: note: (near initialization for 'nft_osf_policy')
>> net/netfilter/nft_osf.c:23:3: error: 'NFTA_OSF_LOGLEVEL' undeclared here (not in a function); did you mean 'NFTA_LOG_LEVEL'?
     [NFTA_OSF_LOGLEVEL] = { .type = NLA_U32 },
      ^~~~~~~~~~~~~~~~~
      NFTA_LOG_LEVEL
   net/netfilter/nft_osf.c:23:3: error: array index in initializer not of integer type
   net/netfilter/nft_osf.c:23:3: note: (near initialization for 'nft_osf_policy')
   net/netfilter/nft_osf.c:23:26: error: field name not in record or union initializer
     [NFTA_OSF_LOGLEVEL] = { .type = NLA_U32 },
                             ^
   net/netfilter/nft_osf.c:23:26: note: (near initialization for 'nft_osf_policy')
>> net/netfilter/nft_osf.c:24:3: error: 'NFTA_OSF_TTL' undeclared here (not in a function); did you mean 'NF_OSF_TTL'?
     [NFTA_OSF_TTL]  = { .type = NLA_U32 },
      ^~~~~~~~~~~~
      NF_OSF_TTL
   net/netfilter/nft_osf.c:24:3: error: array index in initializer not of integer type
   net/netfilter/nft_osf.c:24:3: note: (near initialization for 'nft_osf_policy')
   net/netfilter/nft_osf.c:24:22: error: field name not in record or union initializer
     [NFTA_OSF_TTL]  = { .type = NLA_U32 },
                         ^
   net/netfilter/nft_osf.c:24:22: note: (near initialization for 'nft_osf_policy')
   net/netfilter/nft_osf.c:20:32: warning: 'nft_osf_policy' defined but not used [-Wunused-variable]
    static const struct nla_policy nft_osf_policy[NFTA_OSF_MAX + 1] = {
                                   ^~~~~~~~~~~~~~
--
   In file included from include/linux/netfilter/nf_osf.h:1,
                    from net//netfilter/nft_osf.c:2:
>> include/uapi/linux/netfilter/nf_osf.h:66:24: error: 'MAX_IPOPTLEN' undeclared here (not in a function); did you mean 'MAY_OPEN'?
     struct nf_osf_opt opt[MAX_IPOPTLEN];
                           ^~~~~~~~~~~~
                           MAY_OPEN
>> include/uapi/linux/netfilter/nf_osf.h:71:17: error: field 'ip' has incomplete type
     struct iphdr   ip;
                    ^~
>> include/uapi/linux/netfilter/nf_osf.h:72:18: error: field 'tcp' has incomplete type
     struct tcphdr   tcp;
                     ^~~
   net//netfilter/nft_osf.c:20:47: error: 'NFTA_OSF_MAX' undeclared here (not in a function); did you mean 'NFTA_OBJ_MAX'?
    static const struct nla_policy nft_osf_policy[NFTA_OSF_MAX + 1] = {
                                                  ^~~~~~~~~~~~
                                                  NFTA_OBJ_MAX
   net//netfilter/nft_osf.c:21:3: error: 'NFTA_OSF_GENRE' undeclared here (not in a function); did you mean 'NF_OSF_GENRE'?
     [NFTA_OSF_GENRE] = { .type = NLA_STRING, .len = OSF_GENRE_SIZE },
      ^~~~~~~~~~~~~~
      NF_OSF_GENRE
   net//netfilter/nft_osf.c:21:3: error: array index in initializer not of integer type
   net//netfilter/nft_osf.c:21:3: note: (near initialization for 'nft_osf_policy')
   net//netfilter/nft_osf.c:21:23: error: field name not in record or union initializer
     [NFTA_OSF_GENRE] = { .type = NLA_STRING, .len = OSF_GENRE_SIZE },
                          ^
   net//netfilter/nft_osf.c:21:23: note: (near initialization for 'nft_osf_policy')
   net//netfilter/nft_osf.c:21:43: error: field name not in record or union initializer
     [NFTA_OSF_GENRE] = { .type = NLA_STRING, .len = OSF_GENRE_SIZE },
                                              ^
   net//netfilter/nft_osf.c:21:43: note: (near initialization for 'nft_osf_policy')
   net//netfilter/nft_osf.c:22:3: error: 'NFTA_OSF_FLAGS' undeclared here (not in a function); did you mean 'NFTA_FIB_FLAGS'?
     [NFTA_OSF_FLAGS] = { .type = NLA_U32 },
      ^~~~~~~~~~~~~~
      NFTA_FIB_FLAGS
   net//netfilter/nft_osf.c:22:3: error: array index in initializer not of integer type
   net//netfilter/nft_osf.c:22:3: note: (near initialization for 'nft_osf_policy')
   net//netfilter/nft_osf.c:22:23: error: field name not in record or union initializer
     [NFTA_OSF_FLAGS] = { .type = NLA_U32 },
                          ^
   net//netfilter/nft_osf.c:22:23: note: (near initialization for 'nft_osf_policy')
   net//netfilter/nft_osf.c:23:3: error: 'NFTA_OSF_LOGLEVEL' undeclared here (not in a function); did you mean 'NFTA_LOG_LEVEL'?
     [NFTA_OSF_LOGLEVEL] = { .type = NLA_U32 },
      ^~~~~~~~~~~~~~~~~
      NFTA_LOG_LEVEL
   net//netfilter/nft_osf.c:23:3: error: array index in initializer not of integer type
   net//netfilter/nft_osf.c:23:3: note: (near initialization for 'nft_osf_policy')
   net//netfilter/nft_osf.c:23:26: error: field name not in record or union initializer
     [NFTA_OSF_LOGLEVEL] = { .type = NLA_U32 },
                             ^
   net//netfilter/nft_osf.c:23:26: note: (near initialization for 'nft_osf_policy')
   net//netfilter/nft_osf.c:24:3: error: 'NFTA_OSF_TTL' undeclared here (not in a function); did you mean 'NF_OSF_TTL'?
     [NFTA_OSF_TTL]  = { .type = NLA_U32 },
      ^~~~~~~~~~~~
      NF_OSF_TTL
   net//netfilter/nft_osf.c:24:3: error: array index in initializer not of integer type
   net//netfilter/nft_osf.c:24:3: note: (near initialization for 'nft_osf_policy')
   net//netfilter/nft_osf.c:24:22: error: field name not in record or union initializer
     [NFTA_OSF_TTL]  = { .type = NLA_U32 },
                         ^
   net//netfilter/nft_osf.c:24:22: note: (near initialization for 'nft_osf_policy')
   net//netfilter/nft_osf.c:20:32: warning: 'nft_osf_policy' defined but not used [-Wunused-variable]
    static const struct nla_policy nft_osf_policy[NFTA_OSF_MAX + 1] = {
                                   ^~~~~~~~~~~~~~

vim +66 include/uapi/linux/netfilter/nf_osf.h

bfb15f2a9 Fernando Fernandez Mancera 2018-05-03  53  
bfb15f2a9 Fernando Fernandez Mancera 2018-05-03  54  struct nf_osf_user_finger {
bfb15f2a9 Fernando Fernandez Mancera 2018-05-03  55  	struct nf_osf_wc	wss;
bfb15f2a9 Fernando Fernandez Mancera 2018-05-03  56  
bfb15f2a9 Fernando Fernandez Mancera 2018-05-03  57  	__u8	ttl, df;
bfb15f2a9 Fernando Fernandez Mancera 2018-05-03  58  	__u16	ss, mss;
bfb15f2a9 Fernando Fernandez Mancera 2018-05-03  59  	__u16	opt_num;
bfb15f2a9 Fernando Fernandez Mancera 2018-05-03  60  
bfb15f2a9 Fernando Fernandez Mancera 2018-05-03  61  	char	genre[MAXGENRELEN];
bfb15f2a9 Fernando Fernandez Mancera 2018-05-03  62  	char	version[MAXGENRELEN];
bfb15f2a9 Fernando Fernandez Mancera 2018-05-03  63  	char	subtype[MAXGENRELEN];
bfb15f2a9 Fernando Fernandez Mancera 2018-05-03  64  
bfb15f2a9 Fernando Fernandez Mancera 2018-05-03  65  	/* MAX_IPOPTLEN is maximum if all options are NOPs or EOLs */
bfb15f2a9 Fernando Fernandez Mancera 2018-05-03 @66  	struct nf_osf_opt	opt[MAX_IPOPTLEN];
bfb15f2a9 Fernando Fernandez Mancera 2018-05-03  67  };
bfb15f2a9 Fernando Fernandez Mancera 2018-05-03  68  
bfb15f2a9 Fernando Fernandez Mancera 2018-05-03  69  struct nf_osf_nlmsg {
bfb15f2a9 Fernando Fernandez Mancera 2018-05-03  70  	struct nf_osf_user_finger	f;
bfb15f2a9 Fernando Fernandez Mancera 2018-05-03 @71  	struct iphdr			ip;
bfb15f2a9 Fernando Fernandez Mancera 2018-05-03 @72  	struct tcphdr			tcp;
bfb15f2a9 Fernando Fernandez Mancera 2018-05-03  73  };
bfb15f2a9 Fernando Fernandez Mancera 2018-05-03  74  

:::::: The code at line 66 was first introduced by commit
:::::: bfb15f2a95cbbc548b59abf8007d0fdb35fdfee5 netfilter: extract Passive OS fingerprint infrastructure from xt_osf

:::::: TO: Fernando Fernandez Mancera <ffmancera@riseup.net>
:::::: CC: Pablo Neira Ayuso <pablo@netfilter.org>

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation

Patch

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 <ffmancera@riseup.net>");
+MODULE_ALIAS_NFT_EXPR("osf");