Subject: Re: [PATCH v4] add stealth mode

From: Daniel Borkmann <[email-masked]>
Date: Wed, 16 Sep 2015 12:26:57 +0200

On 09/16/2015 11:54 AM, Matteo Croce wrote:
> Add option to disable any reply not related to a listening socket,
> like RST/ACK for TCP and ICMP Port-Unreachable for UDP.
> Also disables ICMP replies to echo request and timestamp.
> The stealth mode can be enabled selectively for a single interface.
>
> Signed-off-by: Matteo Croce <[email-masked]>
> ---
> rebased on 4.3-rc1
>
>   Documentation/networking/ip-sysctl.txt | 14 ++++++++++++++
>   include/linux/inetdevice.h             |  1 +
>   include/linux/ipv6.h                   |  1 +
>   include/uapi/linux/ip.h                |  1 +
>   net/ipv4/devinet.c                     |  1 +
>   net/ipv4/icmp.c                        |  6 ++++++
>   net/ipv4/ip_input.c                    |  5 +++--
>   net/ipv4/tcp_ipv4.c                    |  3 ++-
>   net/ipv4/udp.c                         |  4 +++-
>   net/ipv6/addrconf.c                    |  7 +++++++
>   net/ipv6/icmp.c                        |  3 ++-
>   net/ipv6/ip6_input.c                   |  5 +++--
>   net/ipv6/tcp_ipv6.c                    |  2 +-
>   net/ipv6/udp.c                         |  3 ++-
>   14 files changed, 47 insertions(+), 9 deletions(-)
>
> diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
> index ebe94f2..1d46adc 100644
> --- a/Documentation/networking/ip-sysctl.txt
> +++ b/Documentation/networking/ip-sysctl.txt
> @@ -1206,6 +1206,13 @@ igmp_link_local_mcast_reports - BOOLEAN
>   	224.0.0.X range.
>   	Default TRUE
>
> +stealth - BOOLEAN
> +	Disable any reply not related to a listening socket,
> +	like RST/ACK for TCP and ICMP Port-Unreachable for UDP.
> +	Also disables ICMP replies to echo requests and timestamp
> +	and ICMP errors for unknown protocols.
> +	Default value is 0.
> +

Hmm, what about all other protocols besides TCP/UDP such as SCTP, DCCP,
etc? It seems it gives false expectations in such cases when the user
enables being "stealth", but finds out it has no effect at all there ...
nmap f.e. has a couple of scanning options for SCTP, and at least SCTP
is still relevant in telco space.

I know this question has been asked before, but the only answer on this
was so far: "well, I've never played with SCTP before" ... :/