linux-kernel - [PATCH net-next 1/3] net: ipv4: new arp_accept option to accept garp only if in-network

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Message-Id: <3d46841cb86de597157121c6c1f2dc6a8a8bf981.1657556229.git.jhpark1013@gmail.com>
Date:   Mon, 11 Jul 2022 13:51:16 -0400
From:   Jaehee Park <jhpark1013@...il.com>
To:     netdev@...r.kernel.org
Cc:     davem@...emloft.net, yoshfuji@...ux-ipv6.org, dsahern@...nel.org,
        edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
        shuah@...nel.org, linux-kernel@...r.kernel.org, aajith@...sta.com,
        roopa@...dia.com, aroulin@...dia.com, sbrivio@...hat.com,
        jhpark1013@...il.com
Subject: [PATCH net-next 1/3] net: ipv4: new arp_accept option to accept garp only if in-network

In many deployments, we want the option to not learn a neighbor from
garp if the src ip is not in the subnet of addresses configured on the
interface. net.ipv4.arp_accept sysctl is currently used to control
creation of a neigh from a received garp packet. This patch adds a
new option '2' to net.ipv4.arp_accept which extends option '1' by
including the subnet check.

Signed-off-by: Jaehee Park <jhpark1013@...il.com>
Suggested-by: Roopa Prabhu <roopa@...dia.com>
---
 Documentation/networking/ip-sysctl.rst |  4 +++-
 include/linux/inetdevice.h             |  2 +-
 net/ipv4/arp.c                         | 24 ++++++++++++++++++++++--
 3 files changed, 26 insertions(+), 4 deletions(-)

diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst
index 4c8bbf5acfd1..599373601a2b 100644
--- a/Documentation/networking/ip-sysctl.rst
+++ b/Documentation/networking/ip-sysctl.rst
@@ -1633,12 +1633,14 @@ arp_notify - BOOLEAN
 	     or hardware address changes.
 	 ==  ==========================================================
 
-arp_accept - BOOLEAN
+arp_accept - INTEGER
 	Define behavior for gratuitous ARP frames who's IP is not
 	already present in the ARP table:
 
 	- 0 - don't create new entries in the ARP table
 	- 1 - create new entries in the ARP table
+	- 2 - create new entries only if src ip is in the same subnet as
+	  the configured address on the received interface
 
 	Both replies and requests type gratuitous arp will trigger the
 	ARP table to be updated, if this setting is on.
diff --git a/include/linux/inetdevice.h b/include/linux/inetdevice.h
index ead323243e7b..ddb27fc0ee8c 100644
--- a/include/linux/inetdevice.h
+++ b/include/linux/inetdevice.h
@@ -131,7 +131,7 @@ static inline void ipv4_devconf_setall(struct in_device *in_dev)
 	IN_DEV_ORCONF((in_dev), IGNORE_ROUTES_WITH_LINKDOWN)
 
 #define IN_DEV_ARPFILTER(in_dev)	IN_DEV_ORCONF((in_dev), ARPFILTER)
-#define IN_DEV_ARP_ACCEPT(in_dev)	IN_DEV_ORCONF((in_dev), ARP_ACCEPT)
+#define IN_DEV_ARP_ACCEPT(in_dev)	IN_DEV_MAXCONF((in_dev), ARP_ACCEPT)
 #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)
diff --git a/net/ipv4/arp.c b/net/ipv4/arp.c
index af2f12ffc9ca..5eedb042c50b 100644
--- a/net/ipv4/arp.c
+++ b/net/ipv4/arp.c
@@ -429,6 +429,26 @@ static int arp_ignore(struct in_device *in_dev, __be32 sip, __be32 tip)
 	return !inet_confirm_addr(net, in_dev, sip, tip, scope);
 }
 
+static int arp_accept(struct in_device *in_dev, __be32 sip)
+{
+	struct net *net = dev_net(in_dev->dev);
+	int scope = RT_SCOPE_LINK;
+
+	switch (IN_DEV_ARP_ACCEPT(in_dev)) {
+	case 0: /* don't create new entries from garp */
+		return 0;
+	case 1: /* create new entries from garp */
+		return 1;
+	case 2: /*
+		 * create garp only if sip is in the same subnet
+		 * as an address configured on the incoming interface
+		 */
+		return inet_confirm_addr(net, in_dev, sip, 0, scope) ? 1 : 0;
+	default:
+		return 0;
+	}
+}
+
 static int arp_filter(__be32 sip, __be32 tip, struct net_device *dev)
 {
 	struct rtable *rt;
@@ -868,12 +888,12 @@ static int arp_process(struct net *net, struct sock *sk, struct sk_buff *skb)
 	n = __neigh_lookup(&arp_tbl, &sip, dev, 0);
 
 	addr_type = -1;
-	if (n || IN_DEV_ARP_ACCEPT(in_dev)) {
+	if (n || arp_accept(in_dev, sip)) {
 		is_garp = arp_is_garp(net, dev, &addr_type, arp->ar_op,
 				      sip, tip, sha, tha);
 	}
 
-	if (IN_DEV_ARP_ACCEPT(in_dev)) {
+	if (arp_accept(in_dev, sip)) {
 		/* Unsolicited ARP is not accepted by default.
 		   It is possible, that this option should be enabled for some
 		   devices (strip is candidate)
-- 
2.30.2