GHSA-G3FM-VPQW-G4MF

Vulnerability from github – Published: 2026-04-02 12:31 – Updated: 2026-04-24 15:32
VLAI?
Details

In the Linux kernel, the following vulnerability has been resolved:

clsact: Fix use-after-free in init/destroy rollback asymmetry

Fix a use-after-free in the clsact qdisc upon init/destroy rollback asymmetry. The latter is achieved by first fully initializing a clsact instance, and then in a second step having a replacement failure for the new clsact qdisc instance. clsact_init() initializes ingress first and then takes care of the egress part. This can fail midway, for example, via tcf_block_get_ext(). Upon failure, the kernel will trigger the clsact_destroy() callback.

Commit 1cb6f0bae504 ("bpf: Fix too early release of tcx_entry") details the way how the transition is happening. If tcf_block_get_ext on the q->ingress_block ends up failing, we took the tcx_miniq_inc reference count on the ingress side, but not yet on the egress side. clsact_destroy() tests whether the {ingress,egress}_entry was non-NULL. However, even in midway failure on the replacement, both are in fact non-NULL with a valid egress_entry from the previous clsact instance.

What we really need to test for is whether the qdisc instance-specific ingress or egress side previously got initialized. This adds a small helper for checking the miniq initialization called mini_qdisc_pair_inited, and utilizes that upon clsact_destroy() in order to fix the use-after-free scenario. Convert the ingress_destroy() side as well so both are consistent to each other.

Severity ?
7.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
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{
  "affected": [],
  "aliases": [
    "CVE-2026-23413"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-416"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-04-02T12:16:20Z",
    "severity": "HIGH"
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nclsact: Fix use-after-free in init/destroy rollback asymmetry\n\nFix a use-after-free in the clsact qdisc upon init/destroy rollback asymmetry.\nThe latter is achieved by first fully initializing a clsact instance, and\nthen in a second step having a replacement failure for the new clsact qdisc\ninstance. clsact_init() initializes ingress first and then takes care of the\negress part. This can fail midway, for example, via tcf_block_get_ext(). Upon\nfailure, the kernel will trigger the clsact_destroy() callback.\n\nCommit 1cb6f0bae504 (\"bpf: Fix too early release of tcx_entry\") details the\nway how the transition is happening. If tcf_block_get_ext on the q-\u003eingress_block\nends up failing, we took the tcx_miniq_inc reference count on the ingress\nside, but not yet on the egress side. clsact_destroy() tests whether the\n{ingress,egress}_entry was non-NULL. However, even in midway failure on the\nreplacement, both are in fact non-NULL with a valid egress_entry from the\nprevious clsact instance.\n\nWhat we really need to test for is whether the qdisc instance-specific ingress\nor egress side previously got initialized. This adds a small helper for checking\nthe miniq initialization called mini_qdisc_pair_inited, and utilizes that upon\nclsact_destroy() in order to fix the use-after-free scenario. Convert the\ningress_destroy() side as well so both are consistent to each other.",
  "id": "GHSA-g3fm-vpqw-g4mf",
  "modified": "2026-04-24T15:32:20Z",
  "published": "2026-04-02T12:31:05Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-23413"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/0509b762bc5e8ea7b8391130730c6d8502fc6e69"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/37bef86e5428d59f70a4da82b80f9a8f252fecbe"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/4c9af67f99aa3e51b522c54968ab3ac8272be41c"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/a0671125d4f55e1e98d9bde8a0b671941987e208"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/a73d95b57bf9faebdfed591bcb7ed9292062a84c"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ]
}


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