Design intent of teql is that it is only supposed to be used as root qdisc. We need to check for that constraint. Although not important, I will describe the scenario that unearthed this issue for the curious. GangMin Kim managed to concot a scenario as follows: ROOT qdisc 1:0 (QFQ) ├── class 1:1 (weight=15, lmax=16384) netem with delay 6.4s └── class 1:2 (weight=1, lmax=1514) teql GangMin sends a packet which is enqueued to 1:1 (netem). Any invocation of dequeue by QFQ from this class will not return a packet until after 6.4s. In the meantime, a second packet is sent and it lands on 1:2. teql's enqueue will return success and this will activate class 1:2. Main issue is that teql only updates the parent visible qlen (sch->q.qlen) at dequeue. Since QFQ will only call dequeue if peek succeeds (and teql's peek always returns NULL), dequeue will never be called and thus the qlen will remain as 0. With that in mind, when GangMin updates 1:2's lmax value, the qfq_change_class calls qfq_deact_rm_from_agg. Since the child qdisc's qlen was not incremented, qfq fails to deactivate the class, but still frees its pointers from the aggregate. So when the first packet is rescheduled after 6.4 seconds (netem's delay), a dangling pointer is accessed causing GangMin's causing a UAF. Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Reported-by: GangMin Kim Tested-by: Victor Nogueira Signed-off-by: Jamal Hadi Salim --- net/sched/sch_teql.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/net/sched/sch_teql.c b/net/sched/sch_teql.c index 8badec6d82a2..6e4bdaa876ed 100644 --- a/net/sched/sch_teql.c +++ b/net/sched/sch_teql.c @@ -178,6 +178,11 @@ static int teql_qdisc_init(struct Qdisc *sch, struct nlattr *opt, if (m->dev == dev) return -ELOOP; + if (sch->parent != TC_H_ROOT) { + NL_SET_ERR_MSG_MOD(extack, "teql can only be used as root"); + return -EOPNOTSUPP; + } + q->m = m; skb_queue_head_init(&q->q); -- 2.34.1 This is more of a preventive patch to make the code more consistent and to prevent possible exploits that employ child qlen manipulations on qfq. use cl_is_active instead of relying on the child qdisc's qlen to determine class activation. Fixes: 462dbc9101acd ("pkt_sched: QFQ Plus: fair-queueing service at DRR cost") Signed-off-by: Jamal Hadi Salim --- net/sched/sch_qfq.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/sched/sch_qfq.c b/net/sched/sch_qfq.c index f4013b547438..24ea023e4990 100644 --- a/net/sched/sch_qfq.c +++ b/net/sched/sch_qfq.c @@ -373,7 +373,7 @@ static void qfq_rm_from_agg(struct qfq_sched *q, struct qfq_class *cl) /* Deschedule class and remove it from its parent aggregate. */ static void qfq_deact_rm_from_agg(struct qfq_sched *q, struct qfq_class *cl) { - if (cl->qdisc->q.qlen > 0) /* class is active */ + if (cl_is_active(cl)) /* class is active */ qfq_deactivate_class(q, cl); qfq_rm_from_agg(q, cl); -- 2.34.1 From: Victor Nogueira Add a selftest that attempts to add a teql qdisc as a qfq child. Since teql _must_ be added as a root qdisc, the kernel should reject this. Signed-off-by: Victor Nogueira --- .../tc-testing/tc-tests/qdiscs/teql.json | 25 +++++++++++++++++++ 1 file changed, 25 insertions(+) diff --git a/tools/testing/selftests/tc-testing/tc-tests/qdiscs/teql.json b/tools/testing/selftests/tc-testing/tc-tests/qdiscs/teql.json index e5cc31f265f8..0179c57104ad 100644 --- a/tools/testing/selftests/tc-testing/tc-tests/qdiscs/teql.json +++ b/tools/testing/selftests/tc-testing/tc-tests/qdiscs/teql.json @@ -81,5 +81,30 @@ "$TC qdisc del dev $DUMMY handle 1: root", "$IP link del dev $DUMMY" ] + }, + { + "id": "124e", + "name": "Try to add teql as a child qdisc", + "category": [ + "qdisc", + "ets", + "tbf" + ], + "plugins": { + "requires": [ + "nsPlugin" + ] + }, + "setup": [ + "$TC qdisc add dev $DUMMY root handle 1: qfq", + "$TC class add dev $DUMMY parent 1: classid 1:1 qfq weight 15 maxpkt 16384" + ], + "cmdUnderTest": "$TC qdisc add dev $DUMMY parent 1:1 handle 2:1 teql0", + "expExitCode": "2", + "verifyCmd": "$TC -s -j qdisc ls dev $DUMMY parent 1:1", + "matchJSON": [], + "teardown": [ + "$TC qdisc del dev $DUMMY root handle 1:" + ] } ] -- 2.34.1