From dedd34b0f2310e28c5f6d4875cfbf4b7ed821c01 Mon Sep 17 00:00:00 2001 From: Zijie Huang Date: Sat, 1 Aug 2026 21:42:33 +0800 Subject: [PATCH 1/2] net/sched: reject overly deep qdisc hierarchies Deep qdisc hierarchies can lead to excessive recursion in qdisc tree walkers and exhaust the kernel stack. The existing loop check does not cover the create-and-graft path, so a hierarchy can still be extended by creating a new child qdisc below an already deep parent. Store the hierarchy depth in struct Qdisc and update it when qdiscs are grafted. Reject new child qdiscs once the parent is already at the maximum allowed depth. Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Cc: stable@vger.kernel.org Suggested-by: Jamal Hadi Salim Reported-by: Vega Assisted-by: Codex:gpt-5.4 Signed-off-by: Zijie Huang Signed-off-by: Ren Wei Reviewed-by: Victor Nogueira Link: https://patch.msgid.link/1e9ab39597423fd5d13cfaaf52279b8ee3d9fc3c.1785434373.git.milkory@outlook.com Acked-by: Jamal Hadi Salim Signed-off-by: Paolo Abeni --- include/net/sch_generic.h | 1 + net/sched/sch_api.c | 9 +++++++++ 2 files changed, 10 insertions(+) diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h index 45a1e8c78222..cbc248776511 100644 --- a/include/net/sch_generic.h +++ b/include/net/sch_generic.h @@ -99,6 +99,7 @@ struct Qdisc { struct hlist_node hash; u32 handle; u32 parent; + int depth; struct netdev_queue *dev_queue; diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c index 668bcd60d183..65b35528d125 100644 --- a/net/sched/sch_api.c +++ b/net/sched/sch_api.c @@ -1114,6 +1114,9 @@ static int qdisc_graft(struct net_device *dev, struct Qdisc *parent, unsigned int i, num_q, ingress; struct netdev_queue *dev_queue; + if (new) + new->depth = 0; + ingress = 0; num_q = dev->num_tx_queues; if ((q && q->flags & TCQ_F_INGRESS) || @@ -1211,9 +1214,15 @@ static int qdisc_graft(struct net_device *dev, struct Qdisc *parent, NL_SET_ERR_MSG(extack, "STAB not supported on a non root"); return -EINVAL; } + if (new && parent->depth >= 7) { + NL_SET_ERR_MSG(extack, "Qdisc hierarchy is too deep"); + return -E2BIG; + } err = cops->graft(parent, cl, new, &old, extack); if (err) return err; + if (new) + new->depth = parent->depth + 1; notify_and_destroy(net, skb, n, classid, old, new, extack); } return 0; From d8eb9a06b922418598eac38fb9772ea4e9ef4273 Mon Sep 17 00:00:00 2001 From: Zijie Huang Date: Sat, 1 Aug 2026 21:42:34 +0800 Subject: [PATCH 2/2] selftests/tc-testing: add qdisc hierarchy depth tests Add tdc coverage for the qdisc hierarchy depth limit. The tests verify that the deepest allowed hierarchy can still be created and that adding another child qdisc below it is rejected. Signed-off-by: Zijie Huang Assisted-by: Codex:gpt-5.4 Signed-off-by: Ren Wei Reviewed-by: Victor Nogueira Link: https://patch.msgid.link/5cc2d26a7c8e553759cdd29a3116f843fabc25ba.1785434373.git.milkory@outlook.com Acked-by: Jamal Hadi Salim Signed-off-by: Paolo Abeni --- .../tc-testing/tc-tests/qdiscs/depth.json | 74 +++++++++++++++++++ 1 file changed, 74 insertions(+) create mode 100644 tools/testing/selftests/tc-testing/tc-tests/qdiscs/depth.json diff --git a/tools/testing/selftests/tc-testing/tc-tests/qdiscs/depth.json b/tools/testing/selftests/tc-testing/tc-tests/qdiscs/depth.json new file mode 100644 index 000000000000..48f8683f0d1a --- /dev/null +++ b/tools/testing/selftests/tc-testing/tc-tests/qdiscs/depth.json @@ -0,0 +1,74 @@ +[ + { + "id": "ad43", + "name": "Create qdisc hierarchy at maximum depth", + "category": [ + "qdisc", + "depth" + ], + "plugins": { + "requires": "nsPlugin" + }, + "setup": [ + "$TC qdisc add dev $DUMMY root handle 1: htb default 1", + "$TC class add dev $DUMMY parent 1: classid 1:1 htb rate 10mbit", + "$TC qdisc add dev $DUMMY parent 1:1 handle 2: htb default 1", + "$TC class add dev $DUMMY parent 2: classid 2:1 htb rate 10mbit", + "$TC qdisc add dev $DUMMY parent 2:1 handle 3: htb default 1", + "$TC class add dev $DUMMY parent 3: classid 3:1 htb rate 10mbit", + "$TC qdisc add dev $DUMMY parent 3:1 handle 4: htb default 1", + "$TC class add dev $DUMMY parent 4: classid 4:1 htb rate 10mbit", + "$TC qdisc add dev $DUMMY parent 4:1 handle 5: htb default 1", + "$TC class add dev $DUMMY parent 5: classid 5:1 htb rate 10mbit", + "$TC qdisc add dev $DUMMY parent 5:1 handle 6: htb default 1", + "$TC class add dev $DUMMY parent 6: classid 6:1 htb rate 10mbit", + "$TC qdisc add dev $DUMMY parent 6:1 handle 7: htb default 1", + "$TC class add dev $DUMMY parent 7: classid 7:1 htb rate 10mbit" + ], + "cmdUnderTest": "$TC qdisc add dev $DUMMY parent 7:1 handle 8: htb default 1", + "expExitCode": "0", + "verifyCmd": "$TC qdisc show dev $DUMMY", + "matchPattern": "qdisc htb 8: parent 7:1", + "matchCount": "1", + "teardown": [ + "$TC qdisc del dev $DUMMY root" + ] + }, + { + "id": "c519", + "name": "Reject qdisc hierarchy above maximum depth", + "category": [ + "qdisc", + "depth" + ], + "plugins": { + "requires": "nsPlugin" + }, + "setup": [ + "$TC qdisc add dev $DUMMY root handle 1: htb default 1", + "$TC class add dev $DUMMY parent 1: classid 1:1 htb rate 10mbit", + "$TC qdisc add dev $DUMMY parent 1:1 handle 2: htb default 1", + "$TC class add dev $DUMMY parent 2: classid 2:1 htb rate 10mbit", + "$TC qdisc add dev $DUMMY parent 2:1 handle 3: htb default 1", + "$TC class add dev $DUMMY parent 3: classid 3:1 htb rate 10mbit", + "$TC qdisc add dev $DUMMY parent 3:1 handle 4: htb default 1", + "$TC class add dev $DUMMY parent 4: classid 4:1 htb rate 10mbit", + "$TC qdisc add dev $DUMMY parent 4:1 handle 5: htb default 1", + "$TC class add dev $DUMMY parent 5: classid 5:1 htb rate 10mbit", + "$TC qdisc add dev $DUMMY parent 5:1 handle 6: htb default 1", + "$TC class add dev $DUMMY parent 6: classid 6:1 htb rate 10mbit", + "$TC qdisc add dev $DUMMY parent 6:1 handle 7: htb default 1", + "$TC class add dev $DUMMY parent 7: classid 7:1 htb rate 10mbit", + "$TC qdisc add dev $DUMMY parent 7:1 handle 8: htb default 1", + "$TC class add dev $DUMMY parent 8: classid 8:1 htb rate 10mbit" + ], + "cmdUnderTest": "$TC qdisc add dev $DUMMY parent 8:1 handle 9: htb default 1", + "expExitCode": "2", + "verifyCmd": "$TC qdisc show dev $DUMMY", + "matchPattern": "qdisc htb 9:", + "matchCount": "0", + "teardown": [ + "$TC qdisc del dev $DUMMY root" + ] + } +]