From 3f981138109f63232a5fb7165938d4c945cc1b9d Mon Sep 17 00:00:00 2001 From: Cong Wang Date: Sun, 18 May 2025 15:20:37 -0700 Subject: [PATCH 1/2] sch_hfsc: Fix qlen accounting bug when using peek in hfsc_enqueue() When enqueuing the first packet to an HFSC class, hfsc_enqueue() calls the child qdisc's peek() operation before incrementing sch->q.qlen and sch->qstats.backlog. If the child qdisc uses qdisc_peek_dequeued(), this may trigger an immediate dequeue and potential packet drop. In such cases, qdisc_tree_reduce_backlog() is called, but the HFSC qdisc's qlen and backlog have not yet been updated, leading to inconsistent queue accounting. This can leave an empty HFSC class in the active list, causing further consequences like use-after-free. This patch fixes the bug by moving the increment of sch->q.qlen and sch->qstats.backlog before the call to the child qdisc's peek() operation. This ensures that queue length and backlog are always accurate when packet drops or dequeues are triggered during the peek. Fixes: 12d0ad3be9c3 ("net/sched/sch_hfsc.c: handle corner cases where head may change invalidating calculated deadline") Reported-by: Mingi Cho Signed-off-by: Cong Wang Reviewed-by: Simon Horman Link: https://patch.msgid.link/20250518222038.58538-2-xiyou.wangcong@gmail.com Reviewed-by: Jamal Hadi Salim Signed-off-by: Paolo Abeni --- net/sched/sch_hfsc.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/net/sched/sch_hfsc.c b/net/sched/sch_hfsc.c index cb8c525ea20e..7986145a527c 100644 --- a/net/sched/sch_hfsc.c +++ b/net/sched/sch_hfsc.c @@ -1569,6 +1569,9 @@ hfsc_enqueue(struct sk_buff *skb, struct Qdisc *sch, struct sk_buff **to_free) return err; } + sch->qstats.backlog += len; + sch->q.qlen++; + if (first && !cl->cl_nactive) { if (cl->cl_flags & HFSC_RSC) init_ed(cl, len); @@ -1584,9 +1587,6 @@ hfsc_enqueue(struct sk_buff *skb, struct Qdisc *sch, struct sk_buff **to_free) } - sch->qstats.backlog += len; - sch->q.qlen++; - return NET_XMIT_SUCCESS; } From c3572acffb751af65505511b847f628c872ffae0 Mon Sep 17 00:00:00 2001 From: Cong Wang Date: Sun, 18 May 2025 15:20:38 -0700 Subject: [PATCH 2/2] selftests/tc-testing: Add an HFSC qlen accounting test This test reproduces a scenario where HFSC queue length and backlog accounting can become inconsistent when a peek operation triggers a dequeue and possible drop before the parent qdisc updates its counters. The test sets up a DRR root qdisc with an HFSC class, netem, and blackhole children, and uses Scapy to inject a packet. It helps to verify that HFSC correctly tracks qlen and backlog even when packets are dropped during peek-induced dequeue. Cc: Mingi Cho Signed-off-by: Cong Wang Reviewed-by: Simon Horman Link: https://patch.msgid.link/20250518222038.58538-3-xiyou.wangcong@gmail.com Reviewed-by: Jamal Hadi Salim Signed-off-by: Paolo Abeni --- .../tc-testing/tc-tests/infra/qdiscs.json | 27 +++++++++++++++++++ 1 file changed, 27 insertions(+) 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 a951c0d33cd2..ddc97ecd8b39 100644 --- a/tools/testing/selftests/tc-testing/tc-tests/infra/qdiscs.json +++ b/tools/testing/selftests/tc-testing/tc-tests/infra/qdiscs.json @@ -573,5 +573,32 @@ "teardown": [ "$TC qdisc del dev $DEV1 handle 1: root" ] + }, + { + "id": "831d", + "name": "Test HFSC qlen accounting with DRR/NETEM/BLACKHOLE chain", + "category": ["qdisc", "hfsc", "drr", "netem", "blackhole"], + "plugins": { "requires": ["nsPlugin", "scapyPlugin"] }, + "setup": [ + "$IP link set dev $DEV1 up || true", + "$TC qdisc add dev $DEV1 root handle 1: drr", + "$TC filter add dev $DEV1 parent 1: basic classid 1:1", + "$TC class add dev $DEV1 parent 1: classid 1:1 drr", + "$TC qdisc add dev $DEV1 parent 1:1 handle 2: hfsc def 1", + "$TC class add dev $DEV1 parent 2: classid 2:1 hfsc rt m1 8 d 1 m2 0", + "$TC qdisc add dev $DEV1 parent 2:1 handle 3: netem", + "$TC qdisc add dev $DEV1 parent 3:1 handle 4: blackhole" + ], + "scapy": { + "iface": "$DEV0", + "count": 5, + "packet": "Ether()/IP(dst='10.10.10.1', src='10.10.10.10')/ICMP()" + }, + "cmdUnderTest": "$TC -s qdisc show dev $DEV1", + "expExitCode": "0", + "verifyCmd": "$TC -s qdisc show dev $DEV1", + "matchPattern": "qdisc hfsc", + "matchCount": "1", + "teardown": ["$TC qdisc del dev $DEV1 root handle 1: drr"] } ]