2021-03-01 00:56:19

by Henry Shen

Subject: [PATCH] net:ipv4: Packet is not forwarded if bc_forwarding not configured on ingress interface

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
but the egress interface is. If both the ingress and egress interfaces
are configured with bc_forwarding, the packet can be forwarded
successfully.

This patch is to be inline with Cisco's implementation that packet can be
forwarded if ingress interface is NOT configured with bc_forwarding,
but egress interface is.

Signed-off-by: Henry Shen <[email protected]>
---
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 = true;
+ struct in_device *out_dev;
+ int rcv_local = 0;

/* IP on this device is disabled. */

@@ -2176,12 +2178,20 @@ static int ip_route_input_slow(struct sk_buff *skb, __be32 daddr, __be32 saddr,
}

if (res->type == RTN_BROADCAST) {
+ out_dev = in_dev_get(FIB_RES_DEV(*res));
+ if (!out_dev)
+ goto out;
+
+ if (in_dev == out_dev)
+ rcv_local = 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 = false;
- goto brd_input;
+ if (rcv_local)
+ goto brd_input;
}

if (res->type == 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 != RTN_UNICAST)
- goto martian_destination;
+ if (res->type != RTN_BROADCAST)
+ goto martian_destination;

make_route:
err = ip_mkroute_input(skb, res, in_dev, daddr, saddr, tos, flkeys);
--
2.30.1

2021-03-01 03:51:54

by David Ahern

Subject: Re: [PATCH] net:ipv4: Packet is not forwarded if bc_forwarding not configured on ingress interface

On 2/28/21 5:53 PM, Henry Shen wrote:
> 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
> but the egress interface is. If both the ingress and egress interfaces
> are configured with bc_forwarding, the packet can be forwarded
> successfully.
>
> This patch is to be inline with Cisco's implementation that packet can be
> forwarded if ingress interface is NOT configured with bc_forwarding,
> but egress interface is.
>

In Linux, forwarding decisions are made based on the ingress device, not
the egress device.