From f9e1cd6c99200846b324a8b65f7f31ded74013bd Mon Sep 17 00:00:00 2001
From: "Alexander V. Chernikov" <melifaro@FreeBSD.org>
Date: Fri, 19 Feb 2021 21:09:17 +0000
Subject: Fix arp/ndp deletion broken by 2fe5a79425c7.

Changes in the 2fe5a79425c7 moved dst sockaddr masking from the
 routing control plane to the rtsock code.

It broke arp/ndp deletion.
It turns out, arp/ndp perform RTM_GET request first to get an
 interface index necessary for the deletion.
Then they simply stamp the reply with RTF_LLDATA and set the
 command to RTM_DELETE.
As a result, kernel receives request with non-empty RTA_NETMASK
 and clears RTA_DST host bits before passing the message to the
 lla code.

De facto, the only needed bits are RTA_DST, RTA_GATEWAY and the
 subset of rtm_flags.

With that in mind, fix the interace by clearing RTA_NETMASK
 for every messages with RTF_LLDATA.

While here, cleanup arp/ndp code a bit.

MFC after:	1 day
Reviewed by:	gnn
Differential Revision:	https://reviews.freebsd.org/D28804
---
 sys/net/rtsock.c | 31 +++++++++++++++++++++----------
 1 file changed, 21 insertions(+), 10 deletions(-)

(limited to 'sys')

diff --git a/sys/net/rtsock.c b/sys/net/rtsock.c
index 3c1fea497af6..221661585bbf 100644
--- a/sys/net/rtsock.c
+++ b/sys/net/rtsock.c
@@ -1376,6 +1376,14 @@ cleanup_xaddrs_gateway(struct rt_addrinfo *info)
 	return (0);
 }
 
+static void
+remove_netmask(struct rt_addrinfo *info)
+{
+	info->rti_info[RTAX_NETMASK] = NULL;
+	info->rti_flags |= RTF_HOST;
+	info->rti_addrs &= ~RTA_NETMASK;
+}
+
 #ifdef INET
 static int
 cleanup_xaddrs_inet(struct rt_addrinfo *info)
@@ -1405,11 +1413,8 @@ cleanup_xaddrs_inet(struct rt_addrinfo *info)
 
 	if (mask.s_addr != INADDR_BROADCAST)
 		fill_sockaddr_inet(mask_sa, mask);
-	else {
-		info->rti_info[RTAX_NETMASK] = NULL;
-		info->rti_flags |= RTF_HOST;
-		info->rti_addrs &= ~RTA_NETMASK;
-	}
+	else
+		remove_netmask(info);
 
 	/* Check gateway */
 	if (info->rti_info[RTAX_GATEWAY] != NULL)
@@ -1445,11 +1450,8 @@ cleanup_xaddrs_inet6(struct rt_addrinfo *info)
 
 	if (!IN6_ARE_ADDR_EQUAL(&mask, &in6mask128))
 		fill_sockaddr_inet6(mask_sa, &mask, 0);
-	else {
-		info->rti_info[RTAX_NETMASK] = NULL;
-		info->rti_flags |= RTF_HOST;
-		info->rti_addrs &= ~RTA_NETMASK;
-	}
+	else
+		remove_netmask(info);
 
 	/* Check gateway */
 	if (info->rti_info[RTAX_GATEWAY] != NULL)
@@ -1467,6 +1469,15 @@ cleanup_xaddrs(struct rt_addrinfo *info)
 	if (info->rti_info[RTAX_DST] == NULL)
 		return (EINVAL);
 
+	if (info->rti_flags & RTF_LLDATA) {
+		/*
+		 * arp(8)/ndp(8) sends RTA_NETMASK for the associated
+		 * prefix along with the actual address in RTA_DST.
+		 * Remove netmask to avoid unnecessary address masking.
+		 */
+		remove_netmask(info);
+	}
+
 	switch (info->rti_info[RTAX_DST]->sa_family) {
 #ifdef INET
 	case AF_INET:
-- 
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