Patch "sample: bpf: xdp_router_ipv4: Allow the kernel to send arp requests" has been added to the 5.19-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    sample: bpf: xdp_router_ipv4: Allow the kernel to send arp requests

to the 5.19-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     sample-bpf-xdp_router_ipv4-allow-the-kernel-to-send-.patch
and it can be found in the queue-5.19 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit b87702896f21addc055bcfeef96476e7bcc39f69
Author: Lorenzo Bianconi <lorenzo@xxxxxxxxxx>
Date:   Wed May 25 11:44:27 2022 +0200

    sample: bpf: xdp_router_ipv4: Allow the kernel to send arp requests
    
    [ Upstream commit 200a89e3e88786b52bc1dd5f26a310c097f4c6a7 ]
    
    Forward the packet to the kernel if the gw router mac address is missing
    in to trigger ARP discovery.
    
    Fixes: 85bf1f51691c ("samples: bpf: Convert xdp_router_ipv4 to XDP samples helper")
    Signed-off-by: Lorenzo Bianconi <lorenzo@xxxxxxxxxx>
    Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
    Link: https://lore.kernel.org/bpf/60bde5496d108089080504f58199bcf1143ea938.1653471558.git.lorenzo@xxxxxxxxxx
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/samples/bpf/xdp_router_ipv4.bpf.c b/samples/bpf/xdp_router_ipv4.bpf.c
index 248119ca7938..0643330d1d2e 100644
--- a/samples/bpf/xdp_router_ipv4.bpf.c
+++ b/samples/bpf/xdp_router_ipv4.bpf.c
@@ -150,6 +150,15 @@ int xdp_router_ipv4_prog(struct xdp_md *ctx)
 
 				dest_mac = bpf_map_lookup_elem(&arp_table,
 							       &prefix_value->gw);
+				if (!dest_mac) {
+					/* Forward the packet to the kernel in
+					 * order to trigger ARP discovery for
+					 * the default gw.
+					 */
+					if (rec)
+						NO_TEAR_INC(rec->xdp_pass);
+					return XDP_PASS;
+				}
 			}
 		}