CVE-2026-74663: net/sched: reject overly deep qdisc hierarchies
In the Linux kernel, the following vulnerability has been resolved:
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.
Affected Software
Event History
Frequently Asked Questions
Which qdisc operation could bypass the existing hierarchy-depth protection?
The existing loop check did not cover the create-and-graft path. A new child qdisc could therefore be created beneath an already deep parent, extending the hierarchy beyond the intended limit.
What behavior changes after applying the fix?
The kernel stores qdisc hierarchy depth and updates it during graft operations. It rejects attempts to add a child qdisc when its parent is already at the maximum allowed depth.