Ensure that a duplicating netem cannot exist in a tree with other netems
in both qdisc addition and change. This is meant to prevent the soft
lockup and OOM loop scenario discussed in [1]. Also adjust a HFSC's
re-entrancy test case with netem for this new restriction - KASAN
still triggers upon its failure.

[1] https://lore.kernel.org/netdev/8DuRWwfqjoRDLDmBMlIfbrsZg9Gx50DHJc1ilxsEBNe2D6NMoigR_eIRIG0LOjMc3r10nUUZtArXx4oZBIdUfZQrwjcQhdinnMis_0G7VEk=@willsroot.io/

Signed-off-by: William Liu <will@willsroot.io>
Reviewed-by: Savino Dicanosa <savy@syst3mfailure.io>
---
v1 -> v2:
  - Fixed existing test case for new restrictions
  - Add test cases
  - Use dummy instead of lo
---
 .../tc-testing/tc-tests/infra/qdiscs.json     |  5 +-
 .../tc-testing/tc-tests/qdiscs/netem.json     | 81 +++++++++++++++++++
 2 files changed, 83 insertions(+), 3 deletions(-)

diff --git a/tools/testing/selftests/tc-testing/tc-tests/infra/qdiscs.json b/tools/testing/selftests/tc-testing/tc-tests/infra/qdiscs.json
index 9aa44d8176d9..9acc88297484 100644
--- a/tools/testing/selftests/tc-testing/tc-tests/infra/qdiscs.json
+++ b/tools/testing/selftests/tc-testing/tc-tests/infra/qdiscs.json
@@ -478,7 +478,6 @@
             "$TC qdisc add dev $DUMMY parent 1:1 handle 2:0 netem duplicate 100%",
             "$TC filter add dev $DUMMY parent 1:0 protocol ip prio 1 u32 match ip dst 10.10.10.1/32 flowid 1:1",
             "$TC class add dev $DUMMY parent 1:0 classid 1:2 hfsc ls m2 10Mbit",
-            "$TC qdisc add dev $DUMMY parent 1:2 handle 3:0 netem duplicate 100%",
             "$TC filter add dev $DUMMY parent 1:0 protocol ip prio 2 u32 match ip dst 10.10.10.2/32 flowid 1:2",
             "ping -c 1 10.10.10.1 -I$DUMMY > /dev/null || true",
             "$TC filter del dev $DUMMY parent 1:0 protocol ip prio 1",
@@ -491,8 +490,8 @@
             {
                 "kind": "hfsc",
                 "handle": "1:",
-                "bytes": 392,
-                "packets": 4
+                "bytes": 294,
+                "packets": 3
             }
         ],
         "matchCount": "1",
diff --git a/tools/testing/selftests/tc-testing/tc-tests/qdiscs/netem.json b/tools/testing/selftests/tc-testing/tc-tests/qdiscs/netem.json
index 3c4444961488..718d2df2aafa 100644
--- a/tools/testing/selftests/tc-testing/tc-tests/qdiscs/netem.json
+++ b/tools/testing/selftests/tc-testing/tc-tests/qdiscs/netem.json
@@ -336,5 +336,86 @@
         "teardown": [
             "$TC qdisc del dev $DUMMY handle 1: root"
         ]
+    },
+    {
+        "id": "d34d",
+        "name": "NETEM test qdisc duplication restriction in qdisc tree in netem_change root",
+        "category": ["qdisc", "netem"],
+        "plugins": {
+            "requires": "nsPlugin"
+        },
+        "setup": [
+            "$TC qdisc add dev $DUMMY root handle 1: netem limit 1",
+            "$TC qdisc add dev $DUMMY parent 1: handle 2: netem limit 1"
+        ],
+        "cmdUnderTest": "$TC qdisc change dev $DUMMY handle 1: netem duplicate 50%",
+        "expExitCode": "2",
+        "verifyCmd": "$TC -s qdisc show dev $DUMMY",
+        "matchPattern": "qdisc netem",
+        "matchCount": "2",
+        "teardown": [
+            "$TC qdisc del dev $DUMMY handle 1:0 root"
+        ]
+    },
+    {
+        "id": "b33f",
+        "name": "NETEM test qdisc duplication restriction in qdisc tree in netem_change non-root",
+        "category": ["qdisc", "netem"],
+        "plugins": {
+            "requires": "nsPlugin"
+        },
+        "setup": [
+            "$TC qdisc add dev $DUMMY root handle 1: netem limit 1",
+            "$TC qdisc add dev $DUMMY parent 1: handle 2: netem limit 1"
+        ],
+        "cmdUnderTest": "$TC qdisc change dev $DUMMY handle 2: netem duplicate 50%",
+        "expExitCode": "2",
+        "verifyCmd": "$TC -s qdisc show dev $DUMMY",
+        "matchPattern": "qdisc netem",
+        "matchCount": "2",
+        "teardown": [
+            "$TC qdisc del dev $DUMMY handle 1:0 root"
+        ]
+    },
+    {
+        "id": "cafe",
+        "name": "NETEM test qdisc duplication restriction in qdisc tree",
+        "category": ["qdisc", "netem"],
+        "plugins": {
+            "requires": "nsPlugin"
+        },
+        "setup": [
+            "$TC qdisc add dev $DUMMY root handle 1: netem limit 1 duplicate 100%"
+        ],
+        "cmdUnderTest": "$TC qdisc add dev $DUMMY parent 1: handle 2: netem duplicate 100%",
+        "expExitCode": "2",
+        "verifyCmd": "$TC -s qdisc show dev $DUMMY",
+        "matchPattern": "qdisc netem",
+        "matchCount": "1",
+        "teardown": [
+            "$TC qdisc del dev $DUMMY handle 1:0 root"
+        ]
+    },
+    {
+        "id": "1337",
+        "name": "NETEM test qdisc duplication restriction in qdisc tree across branches",
+        "category": ["qdisc", "netem"],
+        "plugins": {
+            "requires": "nsPlugin"
+        },
+        "setup": [
+            "$TC qdisc add dev $DUMMY parent root handle 1:0 hfsc",
+            "$TC class add dev $DUMMY parent 1:0 classid 1:1 hfsc rt m2 10Mbit",
+            "$TC qdisc add dev $DUMMY parent 1:1 handle 2:0 netem",
+            "$TC class add dev $DUMMY parent 1:0 classid 1:2 hfsc rt m2 10Mbit"
+        ],
+        "cmdUnderTest": "$TC qdisc add dev $DUMMY parent 1:2 handle 3:0 netem duplicate 100%",
+        "expExitCode": "2",
+        "verifyCmd": "$TC -s qdisc show dev $DUMMY",
+        "matchPattern": "qdisc netem",
+        "matchCount": "1",
+        "teardown": [
+            "$TC qdisc del dev $DUMMY handle 1:0 root"
+        ]
     }
 ]
-- 
2.43.0