net/sched: account classifier filter allocations to memcg
Summary
| CVE | CVE-2026-90099 |
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| State | PUBLISHED |
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| Assigner | Linux |
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| Source Priority | CVE Program / NVD first with legacy fallback |
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| Published | 2026-09-17 17:17:01 UTC |
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| Updated | 2026-09-17 17:17:01 UTC |
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| Description | 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. |
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Vendor Declared Affected Products
| Source | Vendor | Product | Version | Platforms |
|---|
| CNA |
Linux |
Linux |
affected 0da974f4f303a6842516b764507e3c0a03f41e5a 18c68c8f3d3ff0a4def1391021b439c4333a6c71 git |
Not specified |
| CNA |
Linux |
Linux |
affected 0da974f4f303a6842516b764507e3c0a03f41e5a 1beb81947eb486716af80db7a584f9e9fef7e003 git |
Not specified |
| CNA |
Linux |
Linux |
affected 2.6.18 |
Not specified |
| CNA |
Linux |
Linux |
unaffected 2.6.18 semver |
Not specified |
| CNA |
Linux |
Linux |
unaffected 7.2.6 7.2.* semver |
Not specified |
| CNA |
Linux |
Linux |
unaffected 7.3-rc1 * original_commit_for_fix |
Not specified |
References
| Reference | Source | Link | Tags |
|---|
| git.kernel.org/stable/c/1beb81947eb486716af80db7a584f9e9fef7e003 |
416baaa9-dc9f-4396-8d5f-8c081fb06d67 |
git.kernel.org |
|
| git.kernel.org/stable/c/18c68c8f3d3ff0a4def1391021b439c4333a6c71 |
416baaa9-dc9f-4396-8d5f-8c081fb06d67 |
git.kernel.org |
|
| CVE Program record |
CVE.ORG |
www.cve.org |
canonical |
| NVD vulnerability detail |
NVD |
nvd.nist.gov |
canonical, analysis |
No vendor comments have been submitted for this CVE.
There are currently no legacy QID mappings associated with this CVE.