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net/sched: reject overly deep qdisc hierarchies

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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: 1da177e4c3 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Suggested-by: Jamal Hadi Salim <jhs@mojatatu.com>
Reported-by: Vega <vega@nebusec.ai>
Assisted-by: Codex:gpt-5.4
Signed-off-by: Zijie Huang <milkory@outlook.com>
Signed-off-by: Ren Wei <enjou1224z@gmail.com>
Reviewed-by: Victor Nogueira <victor@mojatatu.com>
Link: https://patch.msgid.link/1e9ab39597423fd5d13cfaaf52279b8ee3d9fc3c.1785434373.git.milkory@outlook.com
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
This commit is contained in:
Zijie Huang
2026-08-01 21:42:33 +08:00
committed by Paolo Abeni
parent 7e2d693af0
commit dedd34b0f2
2 changed files with 10 additions and 0 deletions
Download Patch File Download Diff File Expand all files Collapse all files

1
include/net/sch_generic.h
View File

@@ -99,6 +99,7 @@ struct Qdisc {
struct hlist_node hash;
u32 handle;
u32 parent;
int depth;
struct netdev_queue *dev_queue;

9
net/sched/sch_api.c
View File

@@ -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;