GHSA-Q65P-8M3G-4FPV

Vulnerability from github – Published: 2026-07-19 18:31 – Updated: 2026-07-20 15:31
VLAI
Details

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

batman-adv: bla: avoid double decrement of bla.num_requests

The bla.num_requests is increased when no request_sent was in progress. And it is decremented in various places (announcement was received, backbone is purged, periodic work). But the check if the request_sent is actually set to a specific state and the atomic_dec/_inc are not safe because they are not atomic (TOCTOU) and multiple such code portions can run concurrently.

At the same time, it is necessary to modify request_sent (state) and bla.num_requests atomically. Otherwise batadv_bla_send_request() might set request_sent to 1 and is interrupted. batadv_handle_announce() can then set request_sent back to 0 and decrement num_requests before batadv_bla_send_request() incremented it.

The two operations must therefore be locked. And since state (request_sent) and wait_periods are only accessed inside this lock, they can be converted to simpler datatypes. And to avoid that the bla.num_requests is touched by a parallel running context with a valid backbone_gw reference after batadv_bla_purge_backbone_gw() ran, a third state "stopped" is required to correctly signal that a backbone_gw is in the state of being cleaned up.

Severity
7.1 (High)
CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H
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{
  "affected": [],
  "aliases": [
    "CVE-2026-64095"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-07-19T16:17:50Z",
    "severity": "HIGH"
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nbatman-adv: bla: avoid double decrement of bla.num_requests\n\nThe bla.num_requests is increased when no request_sent was in progress. And\nit is decremented in various places (announcement was received, backbone is\npurged, periodic work). But the check if the request_sent is actually set\nto a specific state and the atomic_dec/_inc are not safe because they are\nnot atomic (TOCTOU) and multiple such code portions can run concurrently.\n\nAt the same time, it is necessary to modify request_sent (state) and\nbla.num_requests atomically. Otherwise batadv_bla_send_request() might set\nrequest_sent to 1 and is interrupted.  batadv_handle_announce() can then\nset request_sent back to 0 and decrement num_requests before\nbatadv_bla_send_request() incremented it.\n\nThe two operations must therefore be locked. And since state (request_sent)\nand wait_periods are only accessed inside this lock, they can be converted\nto simpler datatypes. And to avoid that the bla.num_requests is touched by\na parallel running context with a valid backbone_gw reference after\nbatadv_bla_purge_backbone_gw() ran, a third state \"stopped\" is required to\ncorrectly signal that a backbone_gw is in the state of being cleaned up.",
  "id": "GHSA-q65p-8m3g-4fpv",
  "modified": "2026-07-20T15:31:59Z",
  "published": "2026-07-19T18:31:51Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-64095"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/1f013bc94154f2e78e97d0296175664224c796e0"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/45384612f29692fbf0c770200361a7acff90125c"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/461f1e3dfb888701895b766446c55db2b10db705"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/5328b95960774f2e189f22485616bc7b8eb2f7e3"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/65497ad155a3246df177b5ef662cd6e5a32cb470"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/83ab69bd12b80f6ea169c8bea6977701b53a043d"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/8ff9c59d1b7b48c2596878341a5310f32895d52b"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/a9393751ecf7e9096f93cb6eed02db4f79125765"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H",
      "type": "CVSS_V3"
    }
  ]
}



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