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Re: [PATCH v2] add stealth mode

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  Re: [PATCH v2] add stealth mode Matteo Croce <matteo@openwrt.org> - 2015-07-02 11:00 +0200
    Re: [PATCH v2] add stealth mode Austin S Hemmelgarn <ahferroin7@gmail.com> - 2015-07-08 15:40 +0200

#1175845 — Re: [PATCH v2] add stealth mode

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 <matteo@openwrt.org>
---
check the patch with checkpatch.pl and add documentation in ip-sysctl.txt

 Documentation/networking/ip-sysctl.txt | 12 ++++++++++++
 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/tcp_ipv4.c                    |  3 ++-
 net/ipv4/udp.c                         |  4 +++-
 net/ipv6/addrconf.c                    |  7 +++++++
 net/ipv6/icmp.c                        |  3 ++-
 net/ipv6/tcp_ipv6.c                    |  2 +-
 net/ipv6/udp.c                         |  3 ++-
 12 files changed, 39 insertions(+), 5 deletions(-)

diff --git a/Documentation/networking/ip-sysctl.txt
b/Documentation/networking/ip-sysctl.txt
index 5fae770..9eed021 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -1181,6 +1181,12 @@ tag - INTEGER
  Allows you to write a number, which can be used as required.
  Default value is 0.

+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.
+ Default value is 0.
+
 Alexey Kuznetsov.
 kuznet@ms2.inr.ac.ru

@@ -1584,6 +1590,12 @@ stable_secret - IPv6 address

  By default the stable secret is unset.

+stealth - BOOLEAN
+ Disable any reply not related to a listening socket,
+ like RST/ACK for TCP and ICMP Port-Unreachable for UDP.
+ Also disables ICMPv6 replies to echo requests.
+ Default value is 0.
+
 icmp/*:
 ratelimit - INTEGER
  Limit the maximal rates for sending ICMPv6 packets.
diff --git a/include/linux/inetdevice.h b/include/linux/inetdevice.h
index a4328ce..a64c01e 100644
--- a/include/linux/inetdevice.h
+++ b/include/linux/inetdevice.h
@@ -128,6 +128,7 @@ static inline void ipv4_devconf_setall(struct
in_device *in_dev)
 #define IN_DEV_ARP_ANNOUNCE(in_dev) IN_DEV_MAXCONF((in_dev), ARP_ANNOUNCE)
 #define IN_DEV_ARP_IGNORE(in_dev) IN_DEV_MAXCONF((in_dev), ARP_IGNORE)
 #define IN_DEV_ARP_NOTIFY(in_dev) IN_DEV_MAXCONF((in_dev), ARP_NOTIFY)
+#define IN_DEV_STEALTH(in_dev) IN_DEV_MAXCONF((in_dev), STEALTH)

 struct in_ifaddr {
  struct hlist_node hash;
diff --git a/include/linux/ipv6.h b/include/linux/ipv6.h
index 82806c6..49494ec 100644
--- a/include/linux/ipv6.h
+++ b/include/linux/ipv6.h
@@ -53,6 +53,7 @@ struct ipv6_devconf {
  __s32           ndisc_notify;
  __s32 suppress_frag_ndisc;
  __s32 accept_ra_mtu;
+ __s32 stealth;
  struct ipv6_stable_secret {
  bool initialized;
  struct in6_addr secret;
diff --git a/include/uapi/linux/ip.h b/include/uapi/linux/ip.h
index 08f894d..4acbf99 100644
--- a/include/uapi/linux/ip.h
+++ b/include/uapi/linux/ip.h
@@ -165,6 +165,7 @@ enum
  IPV4_DEVCONF_IGMPV2_UNSOLICITED_REPORT_INTERVAL,
  IPV4_DEVCONF_IGMPV3_UNSOLICITED_REPORT_INTERVAL,
  IPV4_DEVCONF_IGNORE_ROUTES_WITH_LINKDOWN,
+ IPV4_DEVCONF_STEALTH,
  __IPV4_DEVCONF_MAX
 };

diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
index 7498716..6b9930a 100644
--- a/net/ipv4/devinet.c
+++ b/net/ipv4/devinet.c
@@ -2178,6 +2178,7 @@ static struct devinet_sysctl_table {
       "promote_secondaries"),
  DEVINET_SYSCTL_FLUSHING_ENTRY(ROUTE_LOCALNET,
       "route_localnet"),
+ DEVINET_SYSCTL_RW_ENTRY(STEALTH, "stealth"),
  },
 };

diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c
index f5203fb..e8e71fb 100644
--- a/net/ipv4/icmp.c
+++ b/net/ipv4/icmp.c
@@ -882,6 +882,9 @@ static bool icmp_echo(struct sk_buff *skb)
 {
  struct net *net;

+ if (IN_DEV_STEALTH(skb->dev->ip_ptr))
+ return true;
+
  net = dev_net(skb_dst(skb)->dev);
  if (!net->ipv4.sysctl_icmp_echo_ignore_all) {
  struct icmp_bxm icmp_param;
@@ -915,6 +918,9 @@ static bool icmp_timestamp(struct sk_buff *skb)
  if (skb->len < 4)
  goto out_err;

+ if (IN_DEV_STEALTH(skb->dev->ip_ptr))
+ return true;
+
  /*
  * Fill in the current time as ms since midnight UT:
  */
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index d7d4c2b..6f3e6e9 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -77,6 +77,7 @@
 #include <net/busy_poll.h>

 #include <linux/inet.h>
+#include <linux/inetdevice.h>
 #include <linux/ipv6.h>
 #include <linux/stddef.h>
 #include <linux/proc_fs.h>
@@ -1652,7 +1653,7 @@ csum_error:
  TCP_INC_STATS_BH(net, TCP_MIB_CSUMERRORS);
 bad_packet:
  TCP_INC_STATS_BH(net, TCP_MIB_INERRS);
- } else {
+ } else if (!IN_DEV_STEALTH(skb->dev->ip_ptr)) {
  tcp_v4_send_reset(NULL, skb);
  }

diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 83aa604..780069d 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -96,6 +96,7 @@
 #include <linux/timer.h>
 #include <linux/mm.h>
 #include <linux/inet.h>
+#include <linux/inetdevice.h>
 #include <linux/netdevice.h>
 #include <linux/slab.h>
 #include <net/tcp_states.h>
@@ -1823,7 +1824,8 @@ int __udp4_lib_rcv(struct sk_buff *skb, struct
udp_table *udptable,
  goto csum_error;

  UDP_INC_STATS_BH(net, UDP_MIB_NOPORTS, proto == IPPROTO_UDPLITE);
- icmp_send(skb, ICMP_DEST_UNREACH, ICMP_PORT_UNREACH, 0);
+ if (!IN_DEV_STEALTH(skb->dev->ip_ptr))
+ icmp_send(skb, ICMP_DEST_UNREACH, ICMP_PORT_UNREACH, 0);

  /*
  * Hmm.  We got an UDP packet to a port to which we
diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 21c2c81..b9e44e2 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -5585,6 +5585,13 @@ static struct addrconf_sysctl_table
  .proc_handler = addrconf_sysctl_stable_secret,
  },
  {
+ .procname = "stealth",
+ .data = &ipv6_devconf.stealth,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = proc_dointvec,
+ },
+ {
  /* sentinel */
  }
  },
diff --git a/net/ipv6/icmp.c b/net/ipv6/icmp.c
index 713d743..47797a6 100644
--- a/net/ipv6/icmp.c
+++ b/net/ipv6/icmp.c
@@ -723,7 +723,8 @@ static int icmpv6_rcv(struct sk_buff *skb)

  switch (type) {
  case ICMPV6_ECHO_REQUEST:
- icmpv6_echo_reply(skb);
+ if (!idev->cnf.stealth)
+ icmpv6_echo_reply(skb);
  break;

  case ICMPV6_ECHO_REPLY:
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 6748c42..cb41856 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -1445,7 +1445,7 @@ csum_error:
  TCP_INC_STATS_BH(net, TCP_MIB_CSUMERRORS);
 bad_packet:
  TCP_INC_STATS_BH(net, TCP_MIB_INERRS);
- } else {
+ } else if (!__in6_dev_get(skb->dev)->cnf.stealth) {
  tcp_v6_send_reset(NULL, skb);
  }

diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index e51fc3e..459238bb 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -934,7 +934,8 @@ int __udp6_lib_rcv(struct sk_buff *skb, struct
udp_table *udptable,
  goto csum_error;

  UDP6_INC_STATS_BH(net, UDP_MIB_NOPORTS, proto == IPPROTO_UDPLITE);
- icmpv6_send(skb, ICMPV6_DEST_UNREACH, ICMPV6_PORT_UNREACH, 0);
+ if (!__in6_dev_get(skb->dev)->cnf.stealth)
+ icmpv6_send(skb, ICMPV6_DEST_UNREACH, ICMPV6_PORT_UNREACH, 0);

  kfree_skb(skb);
  return 0;
-- 
2.1.4
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#1179836

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On 2015-07-06 15:44, Matteo Croce wrote:
> 2015-07-06 12:49 GMT+02:00  <Valdis.Kletnieks@vt.edu>:
>> On Thu, 02 Jul 2015 10:56:01 +0200, Matteo Croce said:
>>> 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.
>>
>> A few notes.....
>>
>> 2) You *do* realize that this isn't anywhere near sufficient in order
>> to actually make your machine "invisible", right?  (Hint: What *other*
>> packets can be sent to a machine to provoke a response?)
>
> Other than ICMP, UDP and TCP excluding open TCP/UDP ports?
>
Just to name a few that I know of off the top of my head:
1. IP packets with any protocol number not supported by your current 
kernel (these return a special ICMP message).
2. SCTP INIT and COOKIE_ECHO chunks when you have SCTP enabled in the 
kernel.
3. Theoretically, some IGMP messages.
4. NDP messages.
5. ARP queries looking for the machine's IP addresses.
6. Certain odd flag combinations on single TCP packets (check the 
documentation for Nmap for more info regarding these), which I believe 
(although I may be reading the code wrong) you aren't accounting for.
7. DAD queries.
8. ICMP address mask queries (which you also don't appear to account for).

This is by no means an exhaustive list, but all of them really should be 
addressed if you want to do this properly.

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