net/sched: account classifier filter allocations to memcg

Summary

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: vega@nebusec.ai 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.

Timeline

1. Sep 17, 2026, 4:06 PM UTCCVE published
2. Oct 21, 2026, 12:49 PM UTCRecord last updated

Affected versions

• Linux Linux

  From 0da974f4f303a6842516b764507e3c0a03f41e5a · fixed in 5fbb06d4f3d4c509ffe95572384a498bf319e5bf; From 0da974f4f303a6842516b764507e3c0a03f41e5a · fixed in bf6006cea193cf065f7a64fc7974247f8112af33; From 0da974f4f303a6842516b764507e3c0a03f41e5a · fixed in 68fb30607169c92de57c5c82b6af8a733af1cc09; From 0da974f4f303a6842516b764507e3c0a03f41e5a · fixed in 18c68c8f3d3ff0a4def1391021b439c4333a6c71; From 0da974f4f303a6842516b764507e3c0a03f41e5a · fixed in 1beb81947eb486716af80db7a584f9e9fef7e003

• Linux Linux

  2.6.18

• KernelLinux

  From 2.6.18 · fixed in 6.6.160; From 6.7.0 · fixed in 6.12.114; From 6.13.0 · fixed in 6.18.57; From 6.19.0 · fixed in 7.2.6

References 5