[SRU][P][PATCH v2 07/11] selftests/tc-testing: Add a test case for FQ_CODEL with HTB parent

[Ian Whitfield]

From: Cong Wang <xiyou.wangcong at gmail.com>

Add a test case for FQ_CODEL with HTB parent to verify packet drop
behavior when the queue becomes empty. This helps ensure proper
notification mechanisms between qdiscs.

Note this is best-effort, it is hard to play with those parameters
perfectly to always trigger ->qlen_notify().

Cc: Pedro Tammela <pctammela at mojatatu.com>
Signed-off-by: Cong Wang <xiyou.wangcong at gmail.com>
Reviewed-by: Victor Nogueira <victor at mojatatu.com>
Link: https://patch.msgid.link/20250403211636.166257-2-xiyou.wangcong@gmail.com
Acked-by: Jamal Hadi Salim <jhs at mojatatu.com>
Signed-off-by: Paolo Abeni <pabeni at redhat.com>
(backported from commit cbe9588b12d058cbb16735fd468c82ec4b3d1256)
[ijwhitfield: Adjusted context due to missing commit:
076c70098893 ("selftests: tc-testing: Add TBF with SKBPRIO queue length
corner case test")]
CVE-2025-37798
Signed-off-by: Ian Whitfield <ian.whitfield at canonical.com>
---
 .../tc-testing/tc-tests/infra/qdiscs.json     | 33 ++++++++++++++++++-
 1 file changed, 32 insertions(+), 1 deletion(-)

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 9044ac054167..84b10f4806d9 100644
--- a/tools/testing/selftests/tc-testing/tc-tests/infra/qdiscs.json
+++ b/tools/testing/selftests/tc-testing/tc-tests/infra/qdiscs.json
@@ -126,5 +126,36 @@
             "$TC qdisc del dev $DUMMY root handle 1: drr",
             "$IP addr del 10.10.10.10/24 dev $DUMMY"
         ]
-   }
+    },
+    {
+        "id": "a4bb",
+        "name": "Test FQ_CODEL with HTB parent - force packet drop with empty queue",
+        "category": [
+            "qdisc",
+            "fq_codel",
+            "htb"
+        ],
+        "plugins": {
+            "requires": "nsPlugin"
+        },
+        "setup": [
+            "$IP link set dev $DUMMY up || true",
+            "$IP addr add 10.10.10.10/24 dev $DUMMY || true",
+            "$TC qdisc add dev $DUMMY handle 1: root htb default 10",
+            "$TC class add dev $DUMMY parent 1: classid 1:10 htb rate 1kbit",
+            "$TC qdisc add dev $DUMMY parent 1:10 handle 10: fq_codel memory_limit 1 flows 1 target 0.1ms interval 1ms",
+            "$TC filter add dev $DUMMY parent 1: protocol ip prio 1 u32 match ip protocol 1 0xff flowid 1:10",
+            "ping -c 5 -f -I $DUMMY 10.10.10.1 > /dev/null || true",
+            "sleep 0.1"
+        ],
+        "cmdUnderTest": "$TC -s qdisc show dev $DUMMY",
+        "expExitCode": "0",
+        "verifyCmd": "$TC -s qdisc show dev $DUMMY | grep -A 5 'qdisc fq_codel'",
+        "matchPattern": "dropped [1-9][0-9]*",
+        "matchCount": "1",
+        "teardown": [
+            "$TC qdisc del dev $DUMMY handle 1: root",
+            "$IP addr del 10.10.10.10/24 dev $DUMMY || true"
+        ]
+    }
 ]
-- 
2.43.0