Linux Kernel up to 7.2.5 Network Scheduler Classifier cls_api.c tcf_exts_init_ex/u32_init_knode/basic_change allocation of resources

Summaryinfo

A vulnerability, which was classified as critical, has been found in Linux Kernel up to 7.2.5. This issue affects the function tcf_exts_init_ex/u32_init_knode/basic_change of the file cls_api.c of the component Network Scheduler Classifier. Performing a manipulation results in allocation of resources. This vulnerability is known as CVE-2026-90099. Attacking locally is a requirement. No exploit is available. It is advisable to upgrade the affected component.

Detailsinfo

A vulnerability classified as critical has been found in Linux Kernel up to 7.2.5. This affects the function tcf_exts_init_ex/u32_init_knode/basic_change of the file cls_api.c of the component Network Scheduler Classifier. The manipulation with an unknown input leads to a allocation of resources vulnerability. CWE is classifying the issue as CWE-770. The product allocates a reusable resource or group of resources on behalf of an actor without imposing any restrictions on the size or number of resources that can be allocated, in violation of the intended security policy for that actor. This is going to have an impact on availability. The summary by CVE is:

In the Linux kernel, the following vulnerability has been resolved: net/sched: account classifier filter allocations to memcg Allocations in the tc classifier *_change() paths (filter objects, per-CPU counters, and per-filter aux data) use plain GFP_KERNEL without __GFP_ACCOUNT, allowing unprivileged users to pin kernel memory outside memcg charging. The shared tcf_exts_init_ex() action array allocation in cls_api.c was also uncharged; this patch closes it along with the per-classifier filter-object/percpu/aux allocations that remain unaccounted. Add GFP_KERNEL_ACCOUNT to: - the shared tcf_exts_init_ex() action array (cls_api.c), common to every filter of every classifier (32 pointers, 256 bytes); - the filter-object, per-CPU-counter, and per-filter aux allocations in cls_basic, cls_bpf, cls_cgroup, cls_flow, cls_flower, cls_fw, cls_matchall, cls_route and cls_u32; - the u32_init_knode() replace-path knode allocation (cls_u32.c), which allocates the same struct tc_u_knode + sel.keys on every replace of an existing knode and was missed by the create-path-only conversion. Also fix the cls_basic error path: basic_change() inserts fnew into the IDR before allocating the per-CPU counter. If alloc_percpu() fails the errout path kfree'd fnew without idr_remove, leaving a dangling pointer in the IDR. With GFP_KERNEL_ACCOUNT the percpu alloc becomes failable on demand (memcg at memory.max), making the dead path attacker-reachable and burning the handle permanently. Add the idr_remove on the percpu failure path, matching the basic_set_parms failure-path pattern. Note: [email protected] provided a poc for basic_cls, but it was easy to extend to the other classifiers. Conditions to recreate the bug: - CONFIG_NET_SCHED, CONFIG_NET_CLS_* (the classifier being used), CONFIG_NET_CLS_ACT, CONFIG_MEMCG, CONFIG_USER_NS, CONFIG_NET_NS. - Unprivileged user in a fresh user+network namespace (unshare -Urn), or root with CAP_NET_ADMIN. - Create a large number of tc filters (e.g. tc filter add dev lo ingress ... <classifier> ...) while watching a memcg-limited cgroup: system slab grows far faster than memory.current, pinning kernel memory outside memcg charging.

It is possible to read the advisory at git.kernel.org. This vulnerability is uniquely identified as CVE-2026-90099 since 09/11/2026. The exploitability is told to be easy. Attacking locally is a requirement. Technical details of the vulnerability are known, but there is no available exploit.

Upgrading to version 7.2.6 or 7.3-rc1 eliminates this vulnerability. Applying the patch 18c68c8f3d3ff0a4def1391021b439c4333a6c71/1beb81947eb486716af80db7a584f9e9fef7e003 is able to eliminate this problem. The best possible mitigation is suggested to be upgrading to the latest version.

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Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 7.2.0
• 7.2.1
• 7.2.2
• 7.2.3
• 7.2.4
• 7.2.5

License

• open-source

Website

• Vendor: https://www.kernel.org/

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