Wang reported an illegal configuration [1] where the user attempts to add a child qdisc to the ingress qdisc as follows: tc qdisc add dev eth0 handle ffff:0 ingress tc qdisc add dev eth0 handle ffe0:0 parent ffff:a fq To solve this, we reject any configuration attempt to add a child qdisc to ingress or clsact. [1] https://lore.kernel.org/netdev/20251105022213.1981982-1-wangliang74@huawei.com/ Fixes: 5e50da01d0ce ("[NET_SCHED]: Fix endless loops (part 2): "simple" qdiscs") Reported-by: Wang Liang Closes: https://lore.kernel.org/netdev/20251105022213.1981982-1-wangliang74@huawei.com/ Reviewed-by: Pedro Tammela Acked-by: Jamal Hadi Salim Signed-off-by: Victor Nogueira --- net/sched/sch_api.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c index 1e058b46d3e1..f56b18c8aebf 100644 --- a/net/sched/sch_api.c +++ b/net/sched/sch_api.c @@ -1599,6 +1599,11 @@ static int __tc_modify_qdisc(struct sk_buff *skb, struct nlmsghdr *n, NL_SET_ERR_MSG(extack, "Failed to find specified qdisc"); return -ENOENT; } + if (p->flags & TCQ_F_INGRESS) { + NL_SET_ERR_MSG(extack, + "Cannot add children to ingress/clsact qdisc"); + return -EOPNOTSUPP; + } q = qdisc_leaf(p, clid, extack); if (IS_ERR(q)) return PTR_ERR(q); -- 2.51.0