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From:   Henry Shen <henry.shen@alliedtelesis.co.nz>
To:     davem@davemloft.net
Cc:     yoshfuji@linux-ipv6.org, dsahern@kernel.org, kuba@kernel.org,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        chris.packham@alliedtelesis.co.nz,
        Henry Shen <henry.shen@alliedtelesis.co.nz>
Subject: [PATCH] net:ipv4: Packet is not forwarded when ingress interface is not configured with bc_forwarding
Date:   Mon,  1 Mar 2021 12:52:24 +1300
Message-Id: <20210228235224.30445-2-henry.shen@alliedtelesis.co.nz>
In-Reply-To: <20210228235224.30445-1-henry.shen@alliedtelesis.co.nz>
References: <20210228235224.30445-1-henry.shen@alliedtelesis.co.nz>
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When an IPv4 packet with a destination address of broadcast is received
on an ingress interface, it will not be forwarded out of the egress
interface if the ingress interface is not configured with bc_forwarding=20
but the egress interface is. If both the ingress and egress interfaces
are configured with bc_forwarding, the packet can be forwarded successful=
ly.

This patch is to be inline with Cisco's implementation that packet can be=
=20
forwarded if ingress interface is NOT configured with bc_forwarding,=20
but egress interface is.
---
 net/ipv4/route.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 02d81d79deeb..d082b199b8c6 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -2101,6 +2101,8 @@ static int ip_route_input_slow(struct sk_buff *skb,=
 __be32 daddr, __be32 saddr,
 	struct rtable	*rth;
 	struct flowi4	fl4;
 	bool do_cache =3D true;
+	struct in_device *out_dev;
+	int		rcv_local =3D 0;
=20
 	/* IP on this device is disabled. */
=20
@@ -2176,12 +2178,20 @@ static int ip_route_input_slow(struct sk_buff *sk=
b, __be32 daddr, __be32 saddr,
 	}
=20
 	if (res->type =3D=3D RTN_BROADCAST) {
+		out_dev =3D in_dev_get(FIB_RES_DEV(*res));
+		if (!out_dev)
+			goto out;
+
+		if (in_dev =3D=3D out_dev)
+			rcv_local =3D 1;
+		in_dev_put(out_dev);
 		if (IN_DEV_BFORWARD(in_dev))
 			goto make_route;
 		/* not do cache if bc_forwarding is enabled */
 		if (IPV4_DEVCONF_ALL(net, BC_FORWARDING))
 			do_cache =3D false;
-		goto brd_input;
+		if (rcv_local)
+			goto brd_input;
 	}
=20
 	if (res->type =3D=3D RTN_LOCAL) {
@@ -2197,7 +2207,8 @@ static int ip_route_input_slow(struct sk_buff *skb,=
 __be32 daddr, __be32 saddr,
 		goto no_route;
 	}
 	if (res->type !=3D RTN_UNICAST)
-		goto martian_destination;
+		if (res->type !=3D RTN_BROADCAST)
+			goto martian_destination;
=20
 make_route:
 	err =3D ip_mkroute_input(skb, res, in_dev, daddr, saddr, tos, flkeys);
--=20
2.30.1