CVE-2025-21971 — net_sched: Prevent creation of classes with TC_H_ROOT

Affected: Linux

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.

USN-7496-1 — linux, linux-aws, linux-aws-hwe, linux-gcp, linux-gcp-4.15, linux-hwe, linux-kvm, linux-oracle vulnerabilities

Affected: Ubuntu:Pro:16.04:LTS: linux-aws-hwe, Ubuntu:Pro:16.04:LTS: linux-gcp, Ubuntu:Pro:16.04:LTS: linux-hwe, Ubuntu:Pro:16.04:LTS: linux-oracle, Ubuntu:Pro:18.04:LTS: linux, Ubuntu:Pro:18.04:LTS: linux-aws, Ubuntu:Pro:18.04:LTS: linux-gcp-4.15, Ubuntu:Pro:18.04:LTS: linux-kvm, Ubuntu:Pro:18.04:LTS: linux-oracle

Several security issues were discovered in the Linux kernel. An attacker could possibly use these to compromise the system. This update corrects flaws in the following subsystems: - Block layer subsystem; - Character device driver; - Hardware crypto device drivers; - GPU drivers; - Media drivers; - Network drivers; - SCSI subsystem; - USB Gadget drivers; - Framebuffer layer; - Ceph distributed file system; - File systems infrastructure; - JFS file system; - Network file system (NFS) client; - NILFS2 file system; - SMB network file system; - Netfilter; - CAN network layer; - IPv6 networking; - MAC80211 subsystem; - Netlink; - Network traffic control; - SCTP protocol; - TIPC protocol; (CVE-2024-53173, CVE-2024-26689, CVE-2024-46771, CVE-2024-36934, CVE-2023-52458, CVE-2021-47191, CVE-2024-50296, CVE-2024-26974, CVE-2021-47150, CVE-2024-53140, CVE-2025-21971, CVE-2024-50237, CVE-2024-46780, CVE-2023-52741, CVE-2024-56642, CVE-2024-56631, CVE-2024-53063, CVE-2024-36015, CVE-2021-47163, CVE-2024-56651, CVE-2024-49925, CVE-2023-52664, CVE-2021-47219, CVE-2024-50256, CVE-2024-53066, CVE-2024-49944, CVE-2024-56598, CVE-2024-56650, CVE-2024-26996, CVE-2024-35864, CVE-2024-56770, CVE-2024-26915, CVE-2023-52927)

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CVE-2025-21971 — net_sched: Prevent creation of classes with TC_H_ROOT

USN-7496-1 — linux, linux-aws, linux-aws-hwe, linux-gcp, linux-gcp-4.15, linux-hwe, linux-kvm, linux-oracle vulnerabilities