[PATCH net-next V6 3/6] net: add sysctl for enabling RFC 8335 PROBE messages

[Andreas Roeseler <andreas.a.roeseler@gmail.com>]

Section 8 of RFC 8335 specifies potential security concerns of
responding to PROBE requests, and states that nodes that support PROBE
functionality MUST be able to enable/disable responses and that
responses MUST be disabled by default

Signed-off-by: Andreas Roeseler <andreas.a.roeseler@gmail.com>
---
Changes:
v1 -> v2:
 - Combine patches related to sysctl

v2 -> v3:
Suggested by Willem de Bruijn <willemdebruijn.kernel@gmail.com>
 - Use proc_dointvec_minmax with zero and one

v5 -> v6:
 - Add documentation to ip-sysctl.rst
---
 Documentation/networking/ip-sysctl.rst | 6 ++++++
 include/net/netns/ipv4.h               | 1 +
 net/ipv4/sysctl_net_ipv4.c             | 9 +++++++++
 3 files changed, 16 insertions(+)

diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst
index c7952ac5bd2f..4130bce40765 100644
--- a/Documentation/networking/ip-sysctl.rst
+++ b/Documentation/networking/ip-sysctl.rst
@@ -1143,6 +1143,12 @@ icmp_echo_ignore_all - BOOLEAN
 
 	Default: 0
 
+icmp_echo_enable_probe - BOOLEAN
+        If set to one, then the kernel will respond to RFC 8335 PROBE
+        requests sent to it.
+
+        Default: 0
+
 icmp_echo_ignore_broadcasts - BOOLEAN
 	If set non-zero, then the kernel will ignore all ICMP ECHO and
 	TIMESTAMP requests sent to it via broadcast/multicast.
diff --git a/include/net/netns/ipv4.h b/include/net/netns/ipv4.h
index d377266d133f..9c8dd424d79b 100644
--- a/include/net/netns/ipv4.h
+++ b/include/net/netns/ipv4.h
@@ -84,6 +84,7 @@ struct netns_ipv4 {
 #endif
 
 	u8 sysctl_icmp_echo_ignore_all;
+	u8 sysctl_icmp_echo_enable_probe;
 	u8 sysctl_icmp_echo_ignore_broadcasts;
 	u8 sysctl_icmp_ignore_bogus_error_responses;
 	u8 sysctl_icmp_errors_use_inbound_ifaddr;
diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
index 442ff4be1bde..b1a340e8738f 100644
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c
@@ -599,6 +599,15 @@ static struct ctl_table ipv4_net_table[] = {
 		.mode		= 0644,
 		.proc_handler	= proc_dou8vec_minmax,
 	},
+	{
+		.procname	= "icmp_echo_enable_probe",
+		.data		= &init_net.ipv4.sysctl_icmp_echo_enable_probe,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= SYSCTL_ZERO,
+		.extra2		= SYSCTL_ONE
+	},
 	{
 		.procname	= "icmp_echo_ignore_broadcasts",
 		.data		= &init_net.ipv4.sysctl_icmp_echo_ignore_broadcasts,
-- 
2.17.1