The rx-udp-gro-forwarding checks fail with "got 10 packets, expected 1"
on a host where something has a UDP tunnel socket, a vxlan say, and
pass on a host where nothing does. Since commit 36707061d6ba ("udp:
allow forwarding of plain (non-fraglisted) UDP GRO packets") the
feature aggregates only datagrams GRO finds no socket for, and GRO
looks the socket up only once a tunnel socket exists on the host; the
checks send to a socket in the receiving namespace, so they pass only
while nothing looks it up.

Let the destination forward the datagrams to a receiver in a namespace
behind it: no local socket is found there, tunnel or not, and the
checks count what the destination receives as before.

Fixes: 1c3cadbe0242 ("self-tests: add veth tests")
Suggested-by: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
Link: https://lore.kernel.org/netdev/CAF=yD-LZSec9g_0bBgrcQvq2OO1BrxMSRHH=uU7eamCmWcTO_A@mail.gmail.com/
Signed-off-by: Eva Kurchatova <eva.kurchatova@virtuozzo.com>
---
 tools/testing/selftests/net/veth.sh | 26 ++++++++++++++++++++++----
 1 file changed, 22 insertions(+), 4 deletions(-)

diff --git a/tools/testing/selftests/net/veth.sh b/tools/testing/selftests/net/veth.sh
index 8b867e0675a7..be7c6b9213a9 100755
--- a/tools/testing/selftests/net/veth.sh
+++ b/tools/testing/selftests/net/veth.sh
@@ -9,12 +9,17 @@ readonly DST=1
 readonly DST_NAT=100
 readonly NS_SRC=$BASE$SRC
 readonly NS_DST=$BASE$DST
+# The receiver of the GRO checks, behind the destination
+readonly RCV=3
+readonly NS_RCV=$BASE$RCV
 # shellcheck disable=SC2155 # prefer RO variable over return value from cmd
 readonly YNL="$(dirname "$(readlink -f "$0")")/../../../net/ynl/pyynl/cli.py"
 
 # "baremetal" network used for raw UDP traffic
 readonly BM_NET_V4=192.168.1.
 readonly BM_NET_V6=2001:db8::
+# Network between the destination and the receiver
+readonly RCV_NET_V4=192.168.2.
 
 readonly CPUS=`nproc`
 ret=0
@@ -26,7 +31,7 @@ cleanup() {
 	[ -n "${jobs}" ] && kill -1 ${jobs} 2>/dev/null
 	rm -f $STATS
 
-	for ns in $NS_SRC $NS_DST; do
+	for ns in $NS_SRC $NS_DST $NS_RCV; do
 		ip netns del $ns 2>/dev/null
 	done
 }
@@ -48,6 +53,17 @@ create_ns() {
 		ip -n $BASE$ns addr add dev veth$ns $BM_NET_V4$ns/24
 		ip -n $BASE$ns addr add dev veth$ns $BM_NET_V6$ns/64 nodad
 	done
+
+	# Forwarded, the datagrams find no local socket, whatever tunnel the host has
+	ip netns add $NS_RCV
+	ip -n $NS_RCV link set dev lo up
+	ip link add name fwd$DST type veth peer name fwd$RCV
+	ip link set dev fwd$DST netns $NS_DST up
+	ip link set dev fwd$RCV netns $NS_RCV up
+	ip -n $NS_DST addr add dev fwd$DST $RCV_NET_V4$DST/24
+	ip -n $NS_RCV addr add dev fwd$RCV $RCV_NET_V4$RCV/24
+	ip netns exec $NS_DST sysctl -wq net.ipv4.ip_forward=1
+	ip -n $NS_RCV route add default via $RCV_NET_V4$DST
 }
 
 __chk_flag() {
@@ -134,15 +150,17 @@ chk_gro() {
 	local msg="$1"
 	local expected=$2
 
-	ip netns exec $BASE$SRC ping -qc 1 $BM_NET_V4$DST >/dev/null
+	# Taking veth$SRC down drops the route, so set it for every check
+	ip -n $NS_SRC route replace ${RCV_NET_V4}0/24 via $BM_NET_V4$DST
+	ip netns exec $BASE$SRC ping -qc 1 $RCV_NET_V4$RCV >/dev/null
 	NSTAT_HISTORY=$STATS ip netns exec $NS_DST nstat -n
 
 	printf "%-60s" "$msg"
-	ip netns exec $BASE$DST ./udpgso_bench_rx -C 1000 -R 10 &
+	ip netns exec $NS_RCV ./udpgso_bench_rx -C 1000 -R 10 &
 	local spid=$!
 	sleep 0.1
 
-	ip netns exec $NS_SRC ./udpgso_bench_tx -4 -s 13000 -S 1300 -M 1 -D $BM_NET_V4$DST
+	ip netns exec $NS_SRC ./udpgso_bench_tx -4 -s 13000 -S 1300 -M 1 -D $RCV_NET_V4$RCV
 	local retc=$?
 	wait $spid
 	local rets=$?
-- 
2.56.0