[net-next,v2] ipv4: Add support to disable icmp timestamp

The remote host answers to an ICMP timestamp request.
This allows an attacker to know the time and date on your host.

This path is an another way contrast to iptables rules:
iptables -A input -p icmp --icmp-type timestamp-request -j DROP
iptables -A output -p icmp --icmp-type timestamp-reply -j DROP

Default is enabled.

enable:
	sysctl -w net.ipv4.icmp_timestamp_enable=1
disable
	sysctl -w net.ipv4.icmp_timestamp_enable=0
testing:
	hping3 --icmp --icmp-ts -V $IPADDR

Signed-off-by: Weilong Chen <chenweilong@huawei.com>
---
 include/net/ip.h           | 2 ++
 net/ipv4/icmp.c            | 5 +++++
 net/ipv4/sysctl_net_ipv4.c | 8 ++++++++
 3 files changed, 15 insertions(+)

On Tue, May 14, 2019 at 10:56:54AM +0800, Weilong Chen wrote:
> The remote host answers to an ICMP timestamp request.
> This allows an attacker to know the time and date on your host.
> 
> This path is an another way contrast to iptables rules:
> iptables -A input -p icmp --icmp-type timestamp-request -j DROP
> iptables -A output -p icmp --icmp-type timestamp-reply -j DROP
> 
> Default is enabled.
> 
> enable:
> 	sysctl -w net.ipv4.icmp_timestamp_enable=1
> disable
> 	sysctl -w net.ipv4.icmp_timestamp_enable=0
> testing:
> 	hping3 --icmp --icmp-ts -V $IPADDR
> 
> Signed-off-by: Weilong Chen <chenweilong@huawei.com>
> ---

I'm not sure what you are trying to do but this looks like a process
violation:

  - it's exactly the same as the patch rejected yesterday
  - it's marked as "v2" again
  - net-next is closed until the end of merge window anyway

Michal Kubecek

>  include/net/ip.h           | 2 ++
>  net/ipv4/icmp.c            | 5 +++++
>  net/ipv4/sysctl_net_ipv4.c | 8 ++++++++
>  3 files changed, 15 insertions(+)
> 
> diff --git a/include/net/ip.h b/include/net/ip.h
> index 2d3cce7..71840e4 100644
> --- a/include/net/ip.h
> +++ b/include/net/ip.h
> @@ -718,6 +718,8 @@ bool icmp_global_allow(void);
>  extern int sysctl_icmp_msgs_per_sec;
>  extern int sysctl_icmp_msgs_burst;
>  
> +extern int sysctl_icmp_timestamp_enable;
> +
>  #ifdef CONFIG_PROC_FS
>  int ip_misc_proc_init(void);
>  #endif
> diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c
> index f3a5893..5010541 100644
> --- a/net/ipv4/icmp.c
> +++ b/net/ipv4/icmp.c
> @@ -232,6 +232,7 @@ static inline void icmp_xmit_unlock(struct sock *sk)
>  
>  int sysctl_icmp_msgs_per_sec __read_mostly = 1000;
>  int sysctl_icmp_msgs_burst __read_mostly = 50;
> +int sysctl_icmp_timestamp_enable __read_mostly = 1;
>  
>  static struct {
>  	spinlock_t	lock;
> @@ -953,6 +954,10 @@ static bool icmp_echo(struct sk_buff *skb)
>  static bool icmp_timestamp(struct sk_buff *skb)
>  {
>  	struct icmp_bxm icmp_param;
> +
> +	if (!sysctl_icmp_timestamp_enable)
> +		goto out_err;
> +
>  	/*
>  	 *	Too short.
>  	 */
> diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
> index 875867b..1fe467e 100644
> --- a/net/ipv4/sysctl_net_ipv4.c
> +++ b/net/ipv4/sysctl_net_ipv4.c
> @@ -544,6 +544,14 @@ static struct ctl_table ipv4_table[] = {
>  		.extra1		= &zero,
>  	},
>  	{
> +		.procname	= "icmp_timestamp_enable",
> +		.data		= &sysctl_icmp_timestamp_enable,
> +		.maxlen		= sizeof(int),
> +		.mode		= 0644,
> +		.proc_handler	= proc_dointvec_minmax,
> +		.extra1		= &zero,
> +	},
> +	{
>  		.procname	= "udp_mem",
>  		.data		= &sysctl_udp_mem,
>  		.maxlen		= sizeof(sysctl_udp_mem),
> -- 
> 2.7.4
>