CVE-2025-21971 Information

Description

In the Linux kernel the following vulnerability has been resolved:

net_sched: Prevent creation of classes with TC_H_ROOT

The function qdisc_tree_reduce_backlog() uses TC_H_ROOT as a termination condition when traversing up the qdisc tree to update parent backlog counters. However if a class is created with classid TC_H_ROOT the traversal terminates prematurely at this class instead of reaching the actual root qdisc causing parent statistics to be incorrectly maintained. In case of DRR this could lead to a crash as reported by Mingi Cho.

Prevent the creation of any Qdisc class with classid TC_H_ROOT (0xFFFFFFFF) across all qdisc types as suggested by Jamal.

Reference

https://git.kernel.org/stable/c/0c3057a5a04d07120b3d0ec9c79568fceb9c921e https://git.kernel.org/stable/c/5c3ca9cb48b51bd72bf76b8b05e24f3cd53db5e7 https://git.kernel.org/stable/c/78533c4a29ac3aeddce4b481770beaaa4f3bfb67 https://git.kernel.org/stable/c/94edfdfb9505ab608e86599d1d1e38c83816fc1c https://git.kernel.org/stable/c/e5ee00607bbfc97ef1526ea95b6b2458ac9e7cb7