[libnftnl,v5,1/3] src: add ct timeout support

Message ID 20180809193216.13643-1-harshasharmaiitr@gmail.com
State Changes Requested
Delegated to: Pablo Neira
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Series
  • [libnftnl,v5,1/3] src: add ct timeout support
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Commit Message

Harsha Sharma Aug. 9, 2018, 7:32 p.m.
Add support for ct timeout objects, used to assign connection tracking
timeout policies.

Signed-off-by: Harsha Sharma <harshasharmaiitr@gmail.com>
---
Changes in v5:
 - Remove nftnl_timeout_policy_attr_set_u32
 - remove NFTNL_OBJ_CT_TIMEOUT_POLICY
 - remove nftnl_obj_get_void
 - minor changes
Changes in v4:
 - updated include/linux/netfilter/nf_tables.h
Changes in v3:
 - minor changes updated with nft patch
Changes in v2:
 - minor changes

 include/libnftnl/Makefile.am        |   3 +-
 include/libnftnl/cttimeout.h        |  39 ++++
 include/libnftnl/object.h           |   7 +
 include/linux/netfilter/nf_tables.h |  14 +-
 include/obj.h                       |   6 +
 src/Makefile.am                     |   1 +
 src/libnftnl.map                    |   1 +
 src/obj/ct_timeout.c                | 369 ++++++++++++++++++++++++++++++++++++
 src/object.c                        |   4 +-
 9 files changed, 441 insertions(+), 3 deletions(-)
 create mode 100644 include/libnftnl/cttimeout.h
 create mode 100644 src/obj/ct_timeout.c

Comments

Pablo Neira Ayuso Aug. 10, 2018, 11:46 a.m. | #1
Hi Harsha,

This looks mostly good, a few comments, see below.

On Fri, Aug 10, 2018 at 01:02:16AM +0530, Harsha Sharma wrote:
[...]
> diff --git a/include/libnftnl/Makefile.am b/include/libnftnl/Makefile.am
> index d846a57..a94f414 100644
> --- a/include/libnftnl/Makefile.am
> +++ b/include/libnftnl/Makefile.am
> @@ -10,4 +10,5 @@ pkginclude_HEADERS = batch.h		\
>  		     ruleset.h		\
>  		     common.h		\
>  		     udata.h		\
> -		     gen.h
> +		     gen.h 		\
> +		     cttimeout.h
> diff --git a/include/libnftnl/cttimeout.h b/include/libnftnl/cttimeout.h
> new file mode 100644
> index 0000000..b29ec57
> --- /dev/null
> +++ b/include/libnftnl/cttimeout.h
> @@ -0,0 +1,39 @@
> +#ifndef _LIBNETFILTER_CTTIMEOUT_H_
> +#define _LIBNETFILTER_CTTIMEOUT_H_
> +
> +#include <stdint.h>
> +#include <sys/types.h>
> +#include <linux/netfilter/nfnetlink_conntrack.h>

These includes don't belong here, place them in the corresponding .c
file, they may actually not be needed.

> +
> +#ifdef __cplusplus
> +extern "C" {
> +#endif
> +
> +struct nftnl_obj_ct_timeout;
> +
> +enum nftnl_cttimeout_tcp {
> +	NFTNL_CTTIMEOUT_TCP_SYN_SENT = 0,
> +	NFTNL_CTTIMEOUT_TCP_SYN_RECV,
> +	NFTNL_CTTIMEOUT_TCP_ESTABLISHED,
> +	NFTNL_CTTIMEOUT_TCP_FIN_WAIT,
> +	NFTNL_CTTIMEOUT_TCP_CLOSE_WAIT,
> +	NFTNL_CTTIMEOUT_TCP_LAST_ACK,
> +	NFTNL_CTTIMEOUT_TCP_TIME_WAIT,
> +	NFTNL_CTTIMEOUT_TCP_CLOSE,
> +	NFTNL_CTTIMEOUT_TCP_SYN_SENT2,
> +	NFTNL_CTTIMEOUT_TCP_RETRANS,
> +	NFTNL_CTTIMEOUT_TCP_UNACK,
> +	NFTNL_CTTIMEOUT_TCP_MAX
> +};
> +
> +enum nftnl_cttimeout_udp {
> +	NFTNL_CTTIMEOUT_UDP_UNREPLIED = 0,
> +	NFTNL_CTTIMEOUT_UDP_REPLIED,
> +	NFTNL_CTTIMEOUT_UDP_MAX
> +};
> +
> +#ifdef __cplusplus
> +} /* extern "C" */
> +#endif
> +
> +#endif
> diff --git a/include/libnftnl/object.h b/include/libnftnl/object.h
> index 6f9edfd..5ed6b98 100644
> --- a/include/libnftnl/object.h
> +++ b/include/libnftnl/object.h
> @@ -7,6 +7,7 @@
>  #include <sys/types.h>
>  
>  #include <libnftnl/common.h>
> +#include <libnftnl/cttimeout.h>
>  
>  #ifdef __cplusplus
>  extern "C" {
> @@ -41,6 +42,12 @@ enum {
>  	NFTNL_OBJ_CT_HELPER_L4PROTO,
>  };
>  
> +enum {
> +	NFTNL_OBJ_CT_TIMEOUT_L3PROTO = NFTNL_OBJ_BASE,
> +	NFTNL_OBJ_CT_TIMEOUT_L4PROTO,
> +	NFTNL_OBJ_CT_TIMEOUT_DATA,
> +};
> +
>  enum {
>  	NFTNL_OBJ_LIMIT_RATE	= NFTNL_OBJ_BASE,
>  	NFTNL_OBJ_LIMIT_UNIT,
> diff --git a/include/linux/netfilter/nf_tables.h b/include/linux/netfilter/nf_tables.h
> index 6dc00c6..382ca54 100644
> --- a/include/linux/netfilter/nf_tables.h
> +++ b/include/linux/netfilter/nf_tables.h
> @@ -969,6 +969,7 @@ enum nft_osf_attributes {
>   * @NFT_CT_DST_IP: conntrack layer 3 protocol destination (IPv4 address)
>   * @NFT_CT_SRC_IP6: conntrack layer 3 protocol source (IPv6 address)
>   * @NFT_CT_DST_IP6: conntrack layer 3 protocol destination (IPv6 address)
> + * @NFT_CT_TIMEOUT: connection tracking timeout policy assigned to conntrack
>   */
>  enum nft_ct_keys {
>  	NFT_CT_STATE,
> @@ -994,6 +995,7 @@ enum nft_ct_keys {
>  	NFT_CT_DST_IP,
>  	NFT_CT_SRC_IP6,
>  	NFT_CT_DST_IP6,
> +	NFT_CT_TIMEOUT,
>  	__NFT_CT_MAX
>  };
>  #define NFT_CT_MAX		(__NFT_CT_MAX - 1)
> @@ -1395,6 +1397,15 @@ enum nft_ct_helper_attributes {
>  };
>  #define NFTA_CT_HELPER_MAX	(__NFTA_CT_HELPER_MAX - 1)
>  
> +enum nft_ct_timeout_attributes {
> +	NFTA_CT_TIMEOUT_UNSPEC,
> +	NFTA_CT_TIMEOUT_L3PROTO,
> +	NFTA_CT_TIMEOUT_L4PROTO,
> +	NFTA_CT_TIMEOUT_DATA,
> +	__NFTA_CT_TIMEOUT_MAX,
> +};
> +#define NFTA_CT_TIMEOUT_MAX	(__NFTA_CT_TIMEOUT_MAX - 1)
> +
>  #define NFT_OBJECT_UNSPEC	0
>  #define NFT_OBJECT_COUNTER	1
>  #define NFT_OBJECT_QUOTA	2
> @@ -1402,7 +1413,8 @@ enum nft_ct_helper_attributes {
>  #define NFT_OBJECT_LIMIT	4
>  #define NFT_OBJECT_CONNLIMIT	5
>  #define NFT_OBJECT_TUNNEL	6
> -#define __NFT_OBJECT_MAX	7
> +#define NFT_OBJECT_CT_TIMEOUT	7
> +#define __NFT_OBJECT_MAX	8
>  #define NFT_OBJECT_MAX		(__NFT_OBJECT_MAX - 1)
>  
>  /**
> diff --git a/include/obj.h b/include/obj.h
> index 9363a69..837a54a 100644
> --- a/include/obj.h
> +++ b/include/obj.h
> @@ -36,6 +36,11 @@ struct nftnl_obj {
>  			uint8_t		l4proto;
>  			char		name[16];
>  		} ct_helper;
> +		struct nftnl_obj_ct_timeout {
> +			uint16_t	l3proto;
> +			uint8_t 	l4proto;
> +			uint32_t	*timeout;
> +		} ct_timeout;
>  		struct nftnl_obj_limit {
>  			uint64_t	rate;
>  			uint64_t	unit;
> @@ -91,6 +96,7 @@ struct obj_ops {
>  extern struct obj_ops obj_ops_counter;
>  extern struct obj_ops obj_ops_quota;
>  extern struct obj_ops obj_ops_ct_helper;
> +extern struct obj_ops obj_ops_ct_timeout;
>  extern struct obj_ops obj_ops_limit;
>  extern struct obj_ops obj_ops_tunnel;
>  
> diff --git a/src/Makefile.am b/src/Makefile.am
> index 9a1a3c4..b5ec079 100644
> --- a/src/Makefile.am
> +++ b/src/Makefile.am
> @@ -64,4 +64,5 @@ libnftnl_la_SOURCES = utils.c		\
>  		      obj/quota.c	\
>  		      obj/tunnel.c	\
>  		      obj/limit.c	\
> +		      obj/ct_timeout.c 	\
>  		      libnftnl.map
> diff --git a/src/libnftnl.map b/src/libnftnl.map
> index 0d6b20c..18c2b7a 100644
> --- a/src/libnftnl.map
> +++ b/src/libnftnl.map
> @@ -345,4 +345,5 @@ LIBNFTNL_7 {
>  
>  LIBNFTNL_8 {
>    nftnl_rule_list_insert_at;
> +  nftnl_obj_get;

This is a leftover, because there is no nftnl_obj_get() anymore.

>  } LIBNFTNL_7;
> diff --git a/src/obj/ct_timeout.c b/src/obj/ct_timeout.c
> new file mode 100644
> index 0000000..9701e99
> --- /dev/null
> +++ b/src/obj/ct_timeout.c
> @@ -0,0 +1,369 @@
> +/*
> + * (C) 2018 by Harsha Sharma <harshasharmaiitr@gmail.com>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License as published
> + * by the Free Software Foundation; either version 2 of the License, or
> + * (at your option) any later version.
> + */
> +
> +#include <stdio.h>
> +#include <stdint.h>
> +#include <arpa/inet.h>
> +#include <errno.h>
> +#include <inttypes.h>
> +
> +#include <linux/netfilter/nf_tables.h>
> +
> +#include "internal.h"
> +#include <libmnl/libmnl.h>
> +#include <libnftnl/object.h>
> +#include <libnftnl/cttimeout.h>
> +
> +#include "obj.h"
> +
> +static const char *const tcp_state_to_name[] = {
> +	[NFTNL_CTTIMEOUT_TCP_SYN_SENT]		= "SYN_SENT",
> +	[NFTNL_CTTIMEOUT_TCP_SYN_RECV]		= "SYN_RECV",
> +	[NFTNL_CTTIMEOUT_TCP_ESTABLISHED]	= "ESTABLISHED",
> +	[NFTNL_CTTIMEOUT_TCP_FIN_WAIT]		= "FIN_WAIT",
> +	[NFTNL_CTTIMEOUT_TCP_CLOSE_WAIT]	= "CLOSE_WAIT",
> +	[NFTNL_CTTIMEOUT_TCP_LAST_ACK]		= "LAST_ACK",
> +	[NFTNL_CTTIMEOUT_TCP_TIME_WAIT]		= "TIME_WAIT",
> +	[NFTNL_CTTIMEOUT_TCP_CLOSE]		= "CLOSE",
> +	[NFTNL_CTTIMEOUT_TCP_SYN_SENT2]		= "SYN_SENT2",
> +	[NFTNL_CTTIMEOUT_TCP_RETRANS]		= "RETRANS",
> +	[NFTNL_CTTIMEOUT_TCP_UNACK]		= "UNACKNOWLEDGED",
> +};
> +
> +static uint32_t tcp_dflt_timeout[] = {
> +	[NFTNL_CTTIMEOUT_TCP_SYN_SENT]		= 120,
> +	[NFTNL_CTTIMEOUT_TCP_SYN_RECV]		= 60,
> +	[NFTNL_CTTIMEOUT_TCP_ESTABLISHED]	= 432000,
> +	[NFTNL_CTTIMEOUT_TCP_FIN_WAIT]		= 120,
> +	[NFTNL_CTTIMEOUT_TCP_CLOSE_WAIT]	= 60,
> +	[NFTNL_CTTIMEOUT_TCP_LAST_ACK]		= 30,
> +	[NFTNL_CTTIMEOUT_TCP_TIME_WAIT]		= 120,
> +	[NFTNL_CTTIMEOUT_TCP_CLOSE]		= 10,
> +	[NFTNL_CTTIMEOUT_TCP_SYN_SENT2] 	= 120,
> +	[NFTNL_CTTIMEOUT_TCP_RETRANS]		= 300,
> +	[NFTNL_CTTIMEOUT_TCP_UNACK]		= 300,
> +};
> +
> +static const char *const udp_state_to_name[] = {
> +	[NFTNL_CTTIMEOUT_UDP_UNREPLIED]	= "UNREPLIED",
> +	[NFTNL_CTTIMEOUT_UDP_REPLIED]	= "REPLIED",
> +};
> +
> +static uint32_t udp_dflt_timeout[] = {
> +	[NFTNL_CTTIMEOUT_UDP_UNREPLIED]	= 30,
> +	[NFTNL_CTTIMEOUT_UDP_REPLIED]	= 180,
> +};
> +
> +static struct {
> +	uint32_t attr_max;
> +	const char *const *state_to_name;
> +	uint32_t *dflt_timeout;
> +} timeout_protocol[IPPROTO_MAX] = {
> +	[IPPROTO_TCP]	= {
> +		.attr_max	= NFTNL_CTTIMEOUT_TCP_MAX,
> +		.state_to_name	= tcp_state_to_name,
> +		.dflt_timeout	= tcp_dflt_timeout,
> +	},
> +	[IPPROTO_UDP]	= {
> +		.attr_max	= NFTNL_CTTIMEOUT_UDP_MAX,
> +		.state_to_name	= udp_state_to_name,
> +		.dflt_timeout	= udp_dflt_timeout,
> +	},
> +};
> +
> +struct _container_policy_cb {
> +	unsigned int nlattr_max;
> +	void *tb;
> +};
> +
> +static int
> +nftnl_timeout_policy_attr_set_u32(struct nftnl_obj *e,
> +				 uint32_t type, uint32_t data)
> +{
> +	struct nftnl_obj_ct_timeout *t = nftnl_obj_data(e);
> +	size_t timeout_array_size;
> +
> +	/* Layer 4 protocol needs to be already set. */
> +	if (!(e->flags & (1 << NFTNL_OBJ_CT_TIMEOUT_L4PROTO)))
> +		return -1;
> +	if (t->timeout == NULL) {
> +		/* if not supported, default to generic protocol tracker. */
> +		if (timeout_protocol[t->l4proto].attr_max != 0) {
> +			timeout_array_size = sizeof(uint32_t) *
> +					timeout_protocol[t->l4proto].attr_max;
> +		} else {
> +			timeout_array_size = sizeof(uint32_t) *
> +					timeout_protocol[IPPROTO_RAW].attr_max;
> +		}
> +		t->timeout = calloc(1, timeout_array_size);
> +		if (t->timeout == NULL)
> +			return -1;
> +	}
> +
> +	/* this state does not exists in this protocol tracker.*/
> +	if (type > timeout_protocol[t->l4proto].attr_max)
> +		return -1;
> +
> +	t->timeout[type] = data;
> +
> +	if (!(e->flags & (1 << NFTNL_OBJ_CT_TIMEOUT_DATA)))
> +		e->flags |= (1 << NFTNL_OBJ_CT_TIMEOUT_DATA);
> +
> +	return 0;
> +}
> +
> +static int
> +parse_timeout_attr_policy_cb(const struct nlattr *attr, void *data)
> +{
> +	struct _container_policy_cb *data_cb = data;
> +	const struct nlattr **tb = data_cb->tb;
> +	uint16_t type = mnl_attr_get_type(attr);
> +
> +	if (mnl_attr_type_valid(attr, data_cb->nlattr_max) < 0)
> +		return MNL_CB_OK;
> +
> +	if (type <= data_cb->nlattr_max) {
> +		if (mnl_attr_validate(attr, MNL_TYPE_U32) < 0)
> +			abi_breakage();
> +		tb[type] = attr;
> +	}
> +	return MNL_CB_OK;
> +}
> +
> +static void
> +timeout_parse_attr_data(struct nftnl_obj *e,
> +			const struct nlattr *nest)
> +{
> +	struct nftnl_obj_ct_timeout *t = nftnl_obj_data(e);
> +	unsigned int attr_max = timeout_protocol[t->l4proto].attr_max;
> +	struct nlattr *tb[attr_max];
> +	struct _container_policy_cb cnt = {
> +		.nlattr_max = attr_max,
> +		.tb = tb,
> +	};
> +	unsigned int i;
> +
> +	memset(tb, 0, sizeof(struct nlattr *) * attr_max);
> +
> +	mnl_attr_parse_nested(nest, parse_timeout_attr_policy_cb, &cnt);
> +
> +	for (i = 1; i <= attr_max; i++) {
> +		if (tb[i]) {
> +			nftnl_timeout_policy_attr_set_u32(e, i-1,
> +				ntohl(mnl_attr_get_u32(tb[i])));
> +		}
> +	}
> +}
> +
> +static int nftnl_obj_ct_timeout_set(struct nftnl_obj *e, uint16_t type,
> +				   const void *data, uint32_t data_len)
> +{
> +	struct nftnl_obj_ct_timeout *timeout = nftnl_obj_data(e);
> +
> +	switch (type) {
> +	case NFTNL_OBJ_CT_TIMEOUT_L3PROTO:
> +		timeout->l3proto = *((uint16_t *)data);
> +		break;
> +	case NFTNL_OBJ_CT_TIMEOUT_L4PROTO:
> +		timeout->l4proto = *((uint8_t *)data);
> +		break;
> +	case NFTNL_OBJ_CT_TIMEOUT_DATA:
> +		timeout->timeout = ((uint32_t *)data);
> +		break;
> +	default:
> +		return -1;
> +		}
> +	return 0;
> +}
> +
> +static const void *nftnl_obj_ct_timeout_get(const struct nftnl_obj *e,
> +					   uint16_t type, uint32_t *data_len)
> +{
> +	struct nftnl_obj_ct_timeout *timeout = nftnl_obj_data(e);
> +
> +	switch (type) {
> +	case NFTNL_OBJ_CT_TIMEOUT_L3PROTO:
> +		*data_len = sizeof(timeout->l3proto);
> +		return &timeout->l3proto;
> +	case NFTNL_OBJ_CT_TIMEOUT_L4PROTO:
> +		*data_len = sizeof(timeout->l4proto);
> +		return &timeout->l4proto;
> +	case NFTNL_OBJ_CT_TIMEOUT_DATA:
> +		*data_len = sizeof(timeout->timeout);
> +		return timeout->timeout;
> +	}
> +	return NULL;
> +}
> +
> +static int nftnl_obj_ct_timeout_cb(const struct nlattr *attr, void *data)
> +{
> +	int type = mnl_attr_get_type(attr);
> +	const struct nlattr **tb = data;
> +
> +	if (mnl_attr_type_valid(attr, NFTA_CT_TIMEOUT_MAX) < 0)
> +		return MNL_CB_OK;
> +
> +	switch (type) {
> +	case NFTA_CT_TIMEOUT_L3PROTO:
> +		if (mnl_attr_validate(attr, MNL_TYPE_U16) < 0)
> +			abi_breakage();
> +		break;
> +	case NFTA_CT_TIMEOUT_L4PROTO:
> +		if (mnl_attr_validate(attr, MNL_TYPE_U8) < 0)
> +			abi_breakage();
> +		break;
> +	case NFTA_CT_TIMEOUT_DATA:
> +		if (mnl_attr_validate(attr, MNL_TYPE_NESTED) < 0)
> +			abi_breakage();
> +		break;
> +	}
> +
> +	tb[type] = attr;
> +	return MNL_CB_OK;
> +}
> +
> +static void
> +nftnl_obj_ct_timeout_build(struct nlmsghdr *nlh, const struct nftnl_obj *e)
> +{
> +	struct nftnl_obj_ct_timeout *timeout = nftnl_obj_data(e);
> +	struct nlattr *nest;
> +
> +	if (e->flags & (1 << NFTNL_OBJ_CT_TIMEOUT_L3PROTO))
> +		mnl_attr_put_u16(nlh, NFTA_CT_TIMEOUT_L3PROTO, htons(timeout->l3proto));
> +	if (e->flags & (1 << NFTNL_OBJ_CT_TIMEOUT_L4PROTO))
> +		mnl_attr_put_u8(nlh, NFTA_CT_TIMEOUT_L4PROTO, timeout->l4proto);
> +	if (e->flags & (1 << NFTNL_OBJ_CT_TIMEOUT_DATA)) {
> +		nest = mnl_attr_nest_start(nlh, NFTA_CT_TIMEOUT_DATA);
> +		for (int i = 0; i < timeout_protocol[timeout->l4proto].attr_max; i++) {
> +			if (timeout->timeout[i])
> +				mnl_attr_put_u32(nlh, i+1, htonl(timeout->timeout[i]));
> +		}
> +		mnl_attr_nest_end(nlh, nest);
> +	}
> +}
> +
> +static int
> +nftnl_obj_ct_timeout_parse(struct nftnl_obj *e, struct nlattr *attr)
> +{
> +	struct nftnl_obj_ct_timeout *timeout = nftnl_obj_data(e);
> +	struct nlattr *tb[NFTA_CT_TIMEOUT_MAX + 1] = {};
> +
> +	if (mnl_attr_parse_nested(attr, nftnl_obj_ct_timeout_cb, tb) < 0)
> +		return -1;
> +
> +	if (tb[NFTA_CT_TIMEOUT_L3PROTO]) {
> +		timeout->l3proto = ntohs(mnl_attr_get_u16(tb[NFTA_CT_TIMEOUT_L3PROTO]));
> +		e->flags |= (1 << NFTNL_OBJ_CT_TIMEOUT_L3PROTO);
> +	}
> +	if (tb[NFTA_CT_TIMEOUT_L4PROTO]) {
> +		timeout->l4proto = mnl_attr_get_u8(tb[NFTA_CT_TIMEOUT_L4PROTO]);
> +		e->flags |= (1 << NFTNL_OBJ_CT_TIMEOUT_L4PROTO);
> +	}
> +	if (tb[NFTA_CT_TIMEOUT_DATA]) {
> +		timeout_parse_attr_data(e, tb[NFTA_CT_TIMEOUT_DATA]);
> +		e->flags |= (1 << NFTNL_OBJ_CT_TIMEOUT_DATA);
> +	}
> +	return 0;
> +}
> +
> +static int nftnl_obj_ct_timeout_export(char *buf, size_t size,
> +				   const struct nftnl_obj *e, int type)
> +{
> +	struct nftnl_obj_ct_timeout *timeout = nftnl_obj_data(e);
> +
> +	NFTNL_BUF_INIT(b, buf, size);
> +
> +	if (e->flags & (1 << NFTNL_OBJ_CT_TIMEOUT_L3PROTO))
> +		nftnl_buf_u32(&b, type, timeout->l3proto, FAMILY);
> +	if (e->flags & (1 << NFTNL_OBJ_CT_TIMEOUT_L4PROTO))
> +		nftnl_buf_u32(&b, type, timeout->l4proto, "service");

Hm, why "service" ?

> +	return nftnl_buf_done(&b);
> +}
> +
> +static int nftnl_obj_ct_timeout_snprintf_default(char *buf, size_t len,
> +					       const struct nftnl_obj *e)
> +{
> +	int ret = 0;
> +	int offset = 0, remain = len;
> +
> +	struct nftnl_obj_ct_timeout *timeout = nftnl_obj_data(e);
> +
> +	if (e->flags & (1 << NFTNL_OBJ_CT_TIMEOUT_L3PROTO)) {
> +		ret = snprintf(buf + offset, len, "family %d ",
> +			       timeout->l3proto);
> +		SNPRINTF_BUFFER_SIZE(ret, remain, offset);
> +	}
> +	if (e->flags & (1 << NFTNL_OBJ_CT_TIMEOUT_L4PROTO)) {
> +		ret = snprintf(buf + offset, len, "protocol %d ",
> +				timeout->l4proto);
> +		SNPRINTF_BUFFER_SIZE(ret, remain, offset);
> +	}
> +	if (e->flags & (1 << NFTNL_OBJ_CT_TIMEOUT_DATA)) {
> +		uint8_t l4num = timeout->l4proto;
> +		int i;
> +
> +		/* default to generic protocol tracker. */
> +		if (timeout_protocol[timeout->l4proto].attr_max == 0)
> +			l4num = IPPROTO_RAW;
> +
> +		ret = snprintf(buf + offset, len, "policy = {");
> +		SNPRINTF_BUFFER_SIZE(ret, remain, offset);
> +
> +		for (i = 0; i < timeout_protocol[l4num].attr_max; i++) {
> +			const char *state_name =
> +				timeout_protocol[l4num].state_to_name[i][0] ?
> +				timeout_protocol[l4num].state_to_name[i] :
> +				"UNKNOWN";
> +
> +			if (timeout->timeout[i] != timeout_protocol[l4num].dflt_timeout[i]) {
> +				ret = snprintf(buf + offset, len,
> +					"%s = %u,", state_name, timeout->timeout[i]);
> +				SNPRINTF_BUFFER_SIZE(ret, remain, offset);
> +			}
> +		}
> +
> +		ret = snprintf(buf + offset, len, "}");
> +		SNPRINTF_BUFFER_SIZE(ret, remain, offset);
> +	}
> +	buf[offset] = '\0';
> +
> +	return ret;

Instead, use:

        return offset;

so we return the right string length and hence you can skip the update
on nftnl_obj_snprintf_dflt().

> +

No need for empty line here after return;

> +}
> +
> +static int nftnl_obj_ct_timeout_snprintf(char *buf, size_t len, uint32_t type,
> +				       uint32_t flags,
> +				       const struct nftnl_obj *e)
> +{
> +	if (len)
> +		buf[0] = '\0';
> +
> +	switch (type) {
> +	case NFTNL_OUTPUT_DEFAULT:
> +		return nftnl_obj_ct_timeout_snprintf_default(buf, len, e);
> +	case NFTNL_OUTPUT_JSON:
> +		return nftnl_obj_ct_timeout_export(buf, len, e, type);
> +	default:
> +		break;
> +	}
> +	return -1;
> +}
> +
> +struct obj_ops obj_ops_ct_timeout = {
> +	.name		= "ct_timeout",
> +	.type		= NFT_OBJECT_CT_TIMEOUT,
> +	.alloc_len	= sizeof(struct nftnl_obj_ct_timeout),
> +	.max_attr	= NFTA_CT_TIMEOUT_MAX,
> +	.set		= nftnl_obj_ct_timeout_set,
> +	.get		= nftnl_obj_ct_timeout_get,
> +	.parse		= nftnl_obj_ct_timeout_parse,
> +	.build		= nftnl_obj_ct_timeout_build,
> +	.snprintf	= nftnl_obj_ct_timeout_snprintf,
> +};
> diff --git a/src/object.c b/src/object.c
> index 803b056..931f685 100644
> --- a/src/object.c
> +++ b/src/object.c
> @@ -31,6 +31,7 @@ static struct obj_ops *obj_ops[] = {
>  	[NFT_OBJECT_CT_HELPER]	= &obj_ops_ct_helper,
>  	[NFT_OBJECT_LIMIT]	= &obj_ops_limit,
>  	[NFT_OBJECT_TUNNEL]	= &obj_ops_tunnel,
> +	[NFT_OBJECT_CT_TIMEOUT] = &obj_ops_ct_timeout,
>  };
>  
>  static struct obj_ops *nftnl_obj_ops_lookup(uint32_t type)
> @@ -455,7 +456,8 @@ static int nftnl_obj_snprintf_dflt(char *buf, size_t size,
>  					 obj);
>  		SNPRINTF_BUFFER_SIZE(ret, remain, offset);
>  	}
> -	ret = snprintf(buf + offset, offset, "]");
> +
> +	ret = snprintf(buf + strlen(buf), offset, "]");
>  	SNPRINTF_BUFFER_SIZE(ret, remain, offset);
>  
>  	return offset;
> -- 
> 2.14.1
>

Patch

diff --git a/include/libnftnl/Makefile.am b/include/libnftnl/Makefile.am
index d846a57..a94f414 100644
--- a/include/libnftnl/Makefile.am
+++ b/include/libnftnl/Makefile.am
@@ -10,4 +10,5 @@  pkginclude_HEADERS = batch.h		\
 		     ruleset.h		\
 		     common.h		\
 		     udata.h		\
-		     gen.h
+		     gen.h 		\
+		     cttimeout.h
diff --git a/include/libnftnl/cttimeout.h b/include/libnftnl/cttimeout.h
new file mode 100644
index 0000000..b29ec57
--- /dev/null
+++ b/include/libnftnl/cttimeout.h
@@ -0,0 +1,39 @@ 
+#ifndef _LIBNETFILTER_CTTIMEOUT_H_
+#define _LIBNETFILTER_CTTIMEOUT_H_
+
+#include <stdint.h>
+#include <sys/types.h>
+#include <linux/netfilter/nfnetlink_conntrack.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+struct nftnl_obj_ct_timeout;
+
+enum nftnl_cttimeout_tcp {
+	NFTNL_CTTIMEOUT_TCP_SYN_SENT = 0,
+	NFTNL_CTTIMEOUT_TCP_SYN_RECV,
+	NFTNL_CTTIMEOUT_TCP_ESTABLISHED,
+	NFTNL_CTTIMEOUT_TCP_FIN_WAIT,
+	NFTNL_CTTIMEOUT_TCP_CLOSE_WAIT,
+	NFTNL_CTTIMEOUT_TCP_LAST_ACK,
+	NFTNL_CTTIMEOUT_TCP_TIME_WAIT,
+	NFTNL_CTTIMEOUT_TCP_CLOSE,
+	NFTNL_CTTIMEOUT_TCP_SYN_SENT2,
+	NFTNL_CTTIMEOUT_TCP_RETRANS,
+	NFTNL_CTTIMEOUT_TCP_UNACK,
+	NFTNL_CTTIMEOUT_TCP_MAX
+};
+
+enum nftnl_cttimeout_udp {
+	NFTNL_CTTIMEOUT_UDP_UNREPLIED = 0,
+	NFTNL_CTTIMEOUT_UDP_REPLIED,
+	NFTNL_CTTIMEOUT_UDP_MAX
+};
+
+#ifdef __cplusplus
+} /* extern "C" */
+#endif
+
+#endif
diff --git a/include/libnftnl/object.h b/include/libnftnl/object.h
index 6f9edfd..5ed6b98 100644
--- a/include/libnftnl/object.h
+++ b/include/libnftnl/object.h
@@ -7,6 +7,7 @@ 
 #include <sys/types.h>
 
 #include <libnftnl/common.h>
+#include <libnftnl/cttimeout.h>
 
 #ifdef __cplusplus
 extern "C" {
@@ -41,6 +42,12 @@  enum {
 	NFTNL_OBJ_CT_HELPER_L4PROTO,
 };
 
+enum {
+	NFTNL_OBJ_CT_TIMEOUT_L3PROTO = NFTNL_OBJ_BASE,
+	NFTNL_OBJ_CT_TIMEOUT_L4PROTO,
+	NFTNL_OBJ_CT_TIMEOUT_DATA,
+};
+
 enum {
 	NFTNL_OBJ_LIMIT_RATE	= NFTNL_OBJ_BASE,
 	NFTNL_OBJ_LIMIT_UNIT,
diff --git a/include/linux/netfilter/nf_tables.h b/include/linux/netfilter/nf_tables.h
index 6dc00c6..382ca54 100644
--- a/include/linux/netfilter/nf_tables.h
+++ b/include/linux/netfilter/nf_tables.h
@@ -969,6 +969,7 @@  enum nft_osf_attributes {
  * @NFT_CT_DST_IP: conntrack layer 3 protocol destination (IPv4 address)
  * @NFT_CT_SRC_IP6: conntrack layer 3 protocol source (IPv6 address)
  * @NFT_CT_DST_IP6: conntrack layer 3 protocol destination (IPv6 address)
+ * @NFT_CT_TIMEOUT: connection tracking timeout policy assigned to conntrack
  */
 enum nft_ct_keys {
 	NFT_CT_STATE,
@@ -994,6 +995,7 @@  enum nft_ct_keys {
 	NFT_CT_DST_IP,
 	NFT_CT_SRC_IP6,
 	NFT_CT_DST_IP6,
+	NFT_CT_TIMEOUT,
 	__NFT_CT_MAX
 };
 #define NFT_CT_MAX		(__NFT_CT_MAX - 1)
@@ -1395,6 +1397,15 @@  enum nft_ct_helper_attributes {
 };
 #define NFTA_CT_HELPER_MAX	(__NFTA_CT_HELPER_MAX - 1)
 
+enum nft_ct_timeout_attributes {
+	NFTA_CT_TIMEOUT_UNSPEC,
+	NFTA_CT_TIMEOUT_L3PROTO,
+	NFTA_CT_TIMEOUT_L4PROTO,
+	NFTA_CT_TIMEOUT_DATA,
+	__NFTA_CT_TIMEOUT_MAX,
+};
+#define NFTA_CT_TIMEOUT_MAX	(__NFTA_CT_TIMEOUT_MAX - 1)
+
 #define NFT_OBJECT_UNSPEC	0
 #define NFT_OBJECT_COUNTER	1
 #define NFT_OBJECT_QUOTA	2
@@ -1402,7 +1413,8 @@  enum nft_ct_helper_attributes {
 #define NFT_OBJECT_LIMIT	4
 #define NFT_OBJECT_CONNLIMIT	5
 #define NFT_OBJECT_TUNNEL	6
-#define __NFT_OBJECT_MAX	7
+#define NFT_OBJECT_CT_TIMEOUT	7
+#define __NFT_OBJECT_MAX	8
 #define NFT_OBJECT_MAX		(__NFT_OBJECT_MAX - 1)
 
 /**
diff --git a/include/obj.h b/include/obj.h
index 9363a69..837a54a 100644
--- a/include/obj.h
+++ b/include/obj.h
@@ -36,6 +36,11 @@  struct nftnl_obj {
 			uint8_t		l4proto;
 			char		name[16];
 		} ct_helper;
+		struct nftnl_obj_ct_timeout {
+			uint16_t	l3proto;
+			uint8_t 	l4proto;
+			uint32_t	*timeout;
+		} ct_timeout;
 		struct nftnl_obj_limit {
 			uint64_t	rate;
 			uint64_t	unit;
@@ -91,6 +96,7 @@  struct obj_ops {
 extern struct obj_ops obj_ops_counter;
 extern struct obj_ops obj_ops_quota;
 extern struct obj_ops obj_ops_ct_helper;
+extern struct obj_ops obj_ops_ct_timeout;
 extern struct obj_ops obj_ops_limit;
 extern struct obj_ops obj_ops_tunnel;
 
diff --git a/src/Makefile.am b/src/Makefile.am
index 9a1a3c4..b5ec079 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -64,4 +64,5 @@  libnftnl_la_SOURCES = utils.c		\
 		      obj/quota.c	\
 		      obj/tunnel.c	\
 		      obj/limit.c	\
+		      obj/ct_timeout.c 	\
 		      libnftnl.map
diff --git a/src/libnftnl.map b/src/libnftnl.map
index 0d6b20c..18c2b7a 100644
--- a/src/libnftnl.map
+++ b/src/libnftnl.map
@@ -345,4 +345,5 @@  LIBNFTNL_7 {
 
 LIBNFTNL_8 {
   nftnl_rule_list_insert_at;
+  nftnl_obj_get;
 } LIBNFTNL_7;
diff --git a/src/obj/ct_timeout.c b/src/obj/ct_timeout.c
new file mode 100644
index 0000000..9701e99
--- /dev/null
+++ b/src/obj/ct_timeout.c
@@ -0,0 +1,369 @@ 
+/*
+ * (C) 2018 by Harsha Sharma <harshasharmaiitr@gmail.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published
+ * by the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ */
+
+#include <stdio.h>
+#include <stdint.h>
+#include <arpa/inet.h>
+#include <errno.h>
+#include <inttypes.h>
+
+#include <linux/netfilter/nf_tables.h>
+
+#include "internal.h"
+#include <libmnl/libmnl.h>
+#include <libnftnl/object.h>
+#include <libnftnl/cttimeout.h>
+
+#include "obj.h"
+
+static const char *const tcp_state_to_name[] = {
+	[NFTNL_CTTIMEOUT_TCP_SYN_SENT]		= "SYN_SENT",
+	[NFTNL_CTTIMEOUT_TCP_SYN_RECV]		= "SYN_RECV",
+	[NFTNL_CTTIMEOUT_TCP_ESTABLISHED]	= "ESTABLISHED",
+	[NFTNL_CTTIMEOUT_TCP_FIN_WAIT]		= "FIN_WAIT",
+	[NFTNL_CTTIMEOUT_TCP_CLOSE_WAIT]	= "CLOSE_WAIT",
+	[NFTNL_CTTIMEOUT_TCP_LAST_ACK]		= "LAST_ACK",
+	[NFTNL_CTTIMEOUT_TCP_TIME_WAIT]		= "TIME_WAIT",
+	[NFTNL_CTTIMEOUT_TCP_CLOSE]		= "CLOSE",
+	[NFTNL_CTTIMEOUT_TCP_SYN_SENT2]		= "SYN_SENT2",
+	[NFTNL_CTTIMEOUT_TCP_RETRANS]		= "RETRANS",
+	[NFTNL_CTTIMEOUT_TCP_UNACK]		= "UNACKNOWLEDGED",
+};
+
+static uint32_t tcp_dflt_timeout[] = {
+	[NFTNL_CTTIMEOUT_TCP_SYN_SENT]		= 120,
+	[NFTNL_CTTIMEOUT_TCP_SYN_RECV]		= 60,
+	[NFTNL_CTTIMEOUT_TCP_ESTABLISHED]	= 432000,
+	[NFTNL_CTTIMEOUT_TCP_FIN_WAIT]		= 120,
+	[NFTNL_CTTIMEOUT_TCP_CLOSE_WAIT]	= 60,
+	[NFTNL_CTTIMEOUT_TCP_LAST_ACK]		= 30,
+	[NFTNL_CTTIMEOUT_TCP_TIME_WAIT]		= 120,
+	[NFTNL_CTTIMEOUT_TCP_CLOSE]		= 10,
+	[NFTNL_CTTIMEOUT_TCP_SYN_SENT2] 	= 120,
+	[NFTNL_CTTIMEOUT_TCP_RETRANS]		= 300,
+	[NFTNL_CTTIMEOUT_TCP_UNACK]		= 300,
+};
+
+static const char *const udp_state_to_name[] = {
+	[NFTNL_CTTIMEOUT_UDP_UNREPLIED]	= "UNREPLIED",
+	[NFTNL_CTTIMEOUT_UDP_REPLIED]	= "REPLIED",
+};
+
+static uint32_t udp_dflt_timeout[] = {
+	[NFTNL_CTTIMEOUT_UDP_UNREPLIED]	= 30,
+	[NFTNL_CTTIMEOUT_UDP_REPLIED]	= 180,
+};
+
+static struct {
+	uint32_t attr_max;
+	const char *const *state_to_name;
+	uint32_t *dflt_timeout;
+} timeout_protocol[IPPROTO_MAX] = {
+	[IPPROTO_TCP]	= {
+		.attr_max	= NFTNL_CTTIMEOUT_TCP_MAX,
+		.state_to_name	= tcp_state_to_name,
+		.dflt_timeout	= tcp_dflt_timeout,
+	},
+	[IPPROTO_UDP]	= {
+		.attr_max	= NFTNL_CTTIMEOUT_UDP_MAX,
+		.state_to_name	= udp_state_to_name,
+		.dflt_timeout	= udp_dflt_timeout,
+	},
+};
+
+struct _container_policy_cb {
+	unsigned int nlattr_max;
+	void *tb;
+};
+
+static int
+nftnl_timeout_policy_attr_set_u32(struct nftnl_obj *e,
+				 uint32_t type, uint32_t data)
+{
+	struct nftnl_obj_ct_timeout *t = nftnl_obj_data(e);
+	size_t timeout_array_size;
+
+	/* Layer 4 protocol needs to be already set. */
+	if (!(e->flags & (1 << NFTNL_OBJ_CT_TIMEOUT_L4PROTO)))
+		return -1;
+	if (t->timeout == NULL) {
+		/* if not supported, default to generic protocol tracker. */
+		if (timeout_protocol[t->l4proto].attr_max != 0) {
+			timeout_array_size = sizeof(uint32_t) *
+					timeout_protocol[t->l4proto].attr_max;
+		} else {
+			timeout_array_size = sizeof(uint32_t) *
+					timeout_protocol[IPPROTO_RAW].attr_max;
+		}
+		t->timeout = calloc(1, timeout_array_size);
+		if (t->timeout == NULL)
+			return -1;
+	}
+
+	/* this state does not exists in this protocol tracker.*/
+	if (type > timeout_protocol[t->l4proto].attr_max)
+		return -1;
+
+	t->timeout[type] = data;
+
+	if (!(e->flags & (1 << NFTNL_OBJ_CT_TIMEOUT_DATA)))
+		e->flags |= (1 << NFTNL_OBJ_CT_TIMEOUT_DATA);
+
+	return 0;
+}
+
+static int
+parse_timeout_attr_policy_cb(const struct nlattr *attr, void *data)
+{
+	struct _container_policy_cb *data_cb = data;
+	const struct nlattr **tb = data_cb->tb;
+	uint16_t type = mnl_attr_get_type(attr);
+
+	if (mnl_attr_type_valid(attr, data_cb->nlattr_max) < 0)
+		return MNL_CB_OK;
+
+	if (type <= data_cb->nlattr_max) {
+		if (mnl_attr_validate(attr, MNL_TYPE_U32) < 0)
+			abi_breakage();
+		tb[type] = attr;
+	}
+	return MNL_CB_OK;
+}
+
+static void
+timeout_parse_attr_data(struct nftnl_obj *e,
+			const struct nlattr *nest)
+{
+	struct nftnl_obj_ct_timeout *t = nftnl_obj_data(e);
+	unsigned int attr_max = timeout_protocol[t->l4proto].attr_max;
+	struct nlattr *tb[attr_max];
+	struct _container_policy_cb cnt = {
+		.nlattr_max = attr_max,
+		.tb = tb,
+	};
+	unsigned int i;
+
+	memset(tb, 0, sizeof(struct nlattr *) * attr_max);
+
+	mnl_attr_parse_nested(nest, parse_timeout_attr_policy_cb, &cnt);
+
+	for (i = 1; i <= attr_max; i++) {
+		if (tb[i]) {
+			nftnl_timeout_policy_attr_set_u32(e, i-1,
+				ntohl(mnl_attr_get_u32(tb[i])));
+		}
+	}
+}
+
+static int nftnl_obj_ct_timeout_set(struct nftnl_obj *e, uint16_t type,
+				   const void *data, uint32_t data_len)
+{
+	struct nftnl_obj_ct_timeout *timeout = nftnl_obj_data(e);
+
+	switch (type) {
+	case NFTNL_OBJ_CT_TIMEOUT_L3PROTO:
+		timeout->l3proto = *((uint16_t *)data);
+		break;
+	case NFTNL_OBJ_CT_TIMEOUT_L4PROTO:
+		timeout->l4proto = *((uint8_t *)data);
+		break;
+	case NFTNL_OBJ_CT_TIMEOUT_DATA:
+		timeout->timeout = ((uint32_t *)data);
+		break;
+	default:
+		return -1;
+		}
+	return 0;
+}
+
+static const void *nftnl_obj_ct_timeout_get(const struct nftnl_obj *e,
+					   uint16_t type, uint32_t *data_len)
+{
+	struct nftnl_obj_ct_timeout *timeout = nftnl_obj_data(e);
+
+	switch (type) {
+	case NFTNL_OBJ_CT_TIMEOUT_L3PROTO:
+		*data_len = sizeof(timeout->l3proto);
+		return &timeout->l3proto;
+	case NFTNL_OBJ_CT_TIMEOUT_L4PROTO:
+		*data_len = sizeof(timeout->l4proto);
+		return &timeout->l4proto;
+	case NFTNL_OBJ_CT_TIMEOUT_DATA:
+		*data_len = sizeof(timeout->timeout);
+		return timeout->timeout;
+	}
+	return NULL;
+}
+
+static int nftnl_obj_ct_timeout_cb(const struct nlattr *attr, void *data)
+{
+	int type = mnl_attr_get_type(attr);
+	const struct nlattr **tb = data;
+
+	if (mnl_attr_type_valid(attr, NFTA_CT_TIMEOUT_MAX) < 0)
+		return MNL_CB_OK;
+
+	switch (type) {
+	case NFTA_CT_TIMEOUT_L3PROTO:
+		if (mnl_attr_validate(attr, MNL_TYPE_U16) < 0)
+			abi_breakage();
+		break;
+	case NFTA_CT_TIMEOUT_L4PROTO:
+		if (mnl_attr_validate(attr, MNL_TYPE_U8) < 0)
+			abi_breakage();
+		break;
+	case NFTA_CT_TIMEOUT_DATA:
+		if (mnl_attr_validate(attr, MNL_TYPE_NESTED) < 0)
+			abi_breakage();
+		break;
+	}
+
+	tb[type] = attr;
+	return MNL_CB_OK;
+}
+
+static void
+nftnl_obj_ct_timeout_build(struct nlmsghdr *nlh, const struct nftnl_obj *e)
+{
+	struct nftnl_obj_ct_timeout *timeout = nftnl_obj_data(e);
+	struct nlattr *nest;
+
+	if (e->flags & (1 << NFTNL_OBJ_CT_TIMEOUT_L3PROTO))
+		mnl_attr_put_u16(nlh, NFTA_CT_TIMEOUT_L3PROTO, htons(timeout->l3proto));
+	if (e->flags & (1 << NFTNL_OBJ_CT_TIMEOUT_L4PROTO))
+		mnl_attr_put_u8(nlh, NFTA_CT_TIMEOUT_L4PROTO, timeout->l4proto);
+	if (e->flags & (1 << NFTNL_OBJ_CT_TIMEOUT_DATA)) {
+		nest = mnl_attr_nest_start(nlh, NFTA_CT_TIMEOUT_DATA);
+		for (int i = 0; i < timeout_protocol[timeout->l4proto].attr_max; i++) {
+			if (timeout->timeout[i])
+				mnl_attr_put_u32(nlh, i+1, htonl(timeout->timeout[i]));
+		}
+		mnl_attr_nest_end(nlh, nest);
+	}
+}
+
+static int
+nftnl_obj_ct_timeout_parse(struct nftnl_obj *e, struct nlattr *attr)
+{
+	struct nftnl_obj_ct_timeout *timeout = nftnl_obj_data(e);
+	struct nlattr *tb[NFTA_CT_TIMEOUT_MAX + 1] = {};
+
+	if (mnl_attr_parse_nested(attr, nftnl_obj_ct_timeout_cb, tb) < 0)
+		return -1;
+
+	if (tb[NFTA_CT_TIMEOUT_L3PROTO]) {
+		timeout->l3proto = ntohs(mnl_attr_get_u16(tb[NFTA_CT_TIMEOUT_L3PROTO]));
+		e->flags |= (1 << NFTNL_OBJ_CT_TIMEOUT_L3PROTO);
+	}
+	if (tb[NFTA_CT_TIMEOUT_L4PROTO]) {
+		timeout->l4proto = mnl_attr_get_u8(tb[NFTA_CT_TIMEOUT_L4PROTO]);
+		e->flags |= (1 << NFTNL_OBJ_CT_TIMEOUT_L4PROTO);
+	}
+	if (tb[NFTA_CT_TIMEOUT_DATA]) {
+		timeout_parse_attr_data(e, tb[NFTA_CT_TIMEOUT_DATA]);
+		e->flags |= (1 << NFTNL_OBJ_CT_TIMEOUT_DATA);
+	}
+	return 0;
+}
+
+static int nftnl_obj_ct_timeout_export(char *buf, size_t size,
+				   const struct nftnl_obj *e, int type)
+{
+	struct nftnl_obj_ct_timeout *timeout = nftnl_obj_data(e);
+
+	NFTNL_BUF_INIT(b, buf, size);
+
+	if (e->flags & (1 << NFTNL_OBJ_CT_TIMEOUT_L3PROTO))
+		nftnl_buf_u32(&b, type, timeout->l3proto, FAMILY);
+	if (e->flags & (1 << NFTNL_OBJ_CT_TIMEOUT_L4PROTO))
+		nftnl_buf_u32(&b, type, timeout->l4proto, "service");
+
+	return nftnl_buf_done(&b);
+}
+
+static int nftnl_obj_ct_timeout_snprintf_default(char *buf, size_t len,
+					       const struct nftnl_obj *e)
+{
+	int ret = 0;
+	int offset = 0, remain = len;
+
+	struct nftnl_obj_ct_timeout *timeout = nftnl_obj_data(e);
+
+	if (e->flags & (1 << NFTNL_OBJ_CT_TIMEOUT_L3PROTO)) {
+		ret = snprintf(buf + offset, len, "family %d ",
+			       timeout->l3proto);
+		SNPRINTF_BUFFER_SIZE(ret, remain, offset);
+	}
+	if (e->flags & (1 << NFTNL_OBJ_CT_TIMEOUT_L4PROTO)) {
+		ret = snprintf(buf + offset, len, "protocol %d ",
+				timeout->l4proto);
+		SNPRINTF_BUFFER_SIZE(ret, remain, offset);
+	}
+	if (e->flags & (1 << NFTNL_OBJ_CT_TIMEOUT_DATA)) {
+		uint8_t l4num = timeout->l4proto;
+		int i;
+
+		/* default to generic protocol tracker. */
+		if (timeout_protocol[timeout->l4proto].attr_max == 0)
+			l4num = IPPROTO_RAW;
+
+		ret = snprintf(buf + offset, len, "policy = {");
+		SNPRINTF_BUFFER_SIZE(ret, remain, offset);
+
+		for (i = 0; i < timeout_protocol[l4num].attr_max; i++) {
+			const char *state_name =
+				timeout_protocol[l4num].state_to_name[i][0] ?
+				timeout_protocol[l4num].state_to_name[i] :
+				"UNKNOWN";
+
+			if (timeout->timeout[i] != timeout_protocol[l4num].dflt_timeout[i]) {
+				ret = snprintf(buf + offset, len,
+					"%s = %u,", state_name, timeout->timeout[i]);
+				SNPRINTF_BUFFER_SIZE(ret, remain, offset);
+			}
+		}
+
+		ret = snprintf(buf + offset, len, "}");
+		SNPRINTF_BUFFER_SIZE(ret, remain, offset);
+	}
+	buf[offset] = '\0';
+
+	return ret;
+
+}
+
+static int nftnl_obj_ct_timeout_snprintf(char *buf, size_t len, uint32_t type,
+				       uint32_t flags,
+				       const struct nftnl_obj *e)
+{
+	if (len)
+		buf[0] = '\0';
+
+	switch (type) {
+	case NFTNL_OUTPUT_DEFAULT:
+		return nftnl_obj_ct_timeout_snprintf_default(buf, len, e);
+	case NFTNL_OUTPUT_JSON:
+		return nftnl_obj_ct_timeout_export(buf, len, e, type);
+	default:
+		break;
+	}
+	return -1;
+}
+
+struct obj_ops obj_ops_ct_timeout = {
+	.name		= "ct_timeout",
+	.type		= NFT_OBJECT_CT_TIMEOUT,
+	.alloc_len	= sizeof(struct nftnl_obj_ct_timeout),
+	.max_attr	= NFTA_CT_TIMEOUT_MAX,
+	.set		= nftnl_obj_ct_timeout_set,
+	.get		= nftnl_obj_ct_timeout_get,
+	.parse		= nftnl_obj_ct_timeout_parse,
+	.build		= nftnl_obj_ct_timeout_build,
+	.snprintf	= nftnl_obj_ct_timeout_snprintf,
+};
diff --git a/src/object.c b/src/object.c
index 803b056..931f685 100644
--- a/src/object.c
+++ b/src/object.c
@@ -31,6 +31,7 @@  static struct obj_ops *obj_ops[] = {
 	[NFT_OBJECT_CT_HELPER]	= &obj_ops_ct_helper,
 	[NFT_OBJECT_LIMIT]	= &obj_ops_limit,
 	[NFT_OBJECT_TUNNEL]	= &obj_ops_tunnel,
+	[NFT_OBJECT_CT_TIMEOUT] = &obj_ops_ct_timeout,
 };
 
 static struct obj_ops *nftnl_obj_ops_lookup(uint32_t type)
@@ -455,7 +456,8 @@  static int nftnl_obj_snprintf_dflt(char *buf, size_t size,
 					 obj);
 		SNPRINTF_BUFFER_SIZE(ret, remain, offset);
 	}
-	ret = snprintf(buf + offset, offset, "]");
+
+	ret = snprintf(buf + strlen(buf), offset, "]");
 	SNPRINTF_BUFFER_SIZE(ret, remain, offset);
 
 	return offset;