From a627d36c2a94e18c8c105ae68008786dfd85592e Mon Sep 17 00:00:00 2001 From: Zijie Huang Date: Fri, 21 Aug 2026 10:50:10 -0400 Subject: [PATCH] net/sched: reject overly deep qdisc hierarchies [ Upstream commit dedd34b0f2310e28c5f6d4875cfbf4b7ed821c01 ] 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 [ Dropped the `extack` argument from the `notify_and_destroy()` context line to match 5.15's 6-parameter version. ] Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman --- 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 dd6203f3f0a5..42238e7accb3 100644 --- a/include/net/sch_generic.h +++ b/include/net/sch_generic.h @@ -93,6 +93,7 @@ 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 c67d95a078f7..cbb6c2e0dbff 100644 --- a/net/sched/sch_api.c +++ b/net/sched/sch_api.c @@ -1045,6 +1045,9 @@ 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) || @@ -1124,9 +1127,15 @@ 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); } return 0;