ghsa-grcg-mgx8-mfvf
Vulnerability from github
Published
2025-08-19 18:31
Modified
2025-11-03 18:31
Details

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

eventpoll: Fix semi-unbounded recursion

Ensure that epoll instances can never form a graph deeper than EP_MAX_NESTS+1 links.

Currently, ep_loop_check_proc() ensures that the graph is loop-free and does some recursion depth checks, but those recursion depth checks don't limit the depth of the resulting tree for two reasons:

  • They don't look upwards in the tree.
  • If there are multiple downwards paths of different lengths, only one of the paths is actually considered for the depth check since commit 28d82dc1c4ed ("epoll: limit paths").

Essentially, the current recursion depth check in ep_loop_check_proc() just serves to prevent it from recursing too deeply while checking for loops.

A more thorough check is done in reverse_path_check() after the new graph edge has already been created; this checks, among other things, that no paths going upwards from any non-epoll file with a length of more than 5 edges exist. However, this check does not apply to non-epoll files.

As a result, it is possible to recurse to a depth of at least roughly 500, tested on v6.15. (I am unsure if deeper recursion is possible; and this may have changed with commit 8c44dac8add7 ("eventpoll: Fix priority inversion problem").)

To fix it:

  1. In ep_loop_check_proc(), note the subtree depth of each visited node, and use subtree depths for the total depth calculation even when a subtree has already been visited.
  2. Add ep_get_upwards_depth_proc() for similarly determining the maximum depth of an upwards walk.
  3. In ep_loop_check(), use these values to limit the total path length between epoll nodes to EP_MAX_NESTS edges.
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{
  "affected": [],
  "aliases": [
    "CVE-2025-38614"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2025-08-19T17:15:40Z",
    "severity": null
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\neventpoll: Fix semi-unbounded recursion\n\nEnsure that epoll instances can never form a graph deeper than\nEP_MAX_NESTS+1 links.\n\nCurrently, ep_loop_check_proc() ensures that the graph is loop-free and\ndoes some recursion depth checks, but those recursion depth checks don\u0027t\nlimit the depth of the resulting tree for two reasons:\n\n - They don\u0027t look upwards in the tree.\n - If there are multiple downwards paths of different lengths, only one of\n   the paths is actually considered for the depth check since commit\n   28d82dc1c4ed (\"epoll: limit paths\").\n\nEssentially, the current recursion depth check in ep_loop_check_proc() just\nserves to prevent it from recursing too deeply while checking for loops.\n\nA more thorough check is done in reverse_path_check() after the new graph\nedge has already been created; this checks, among other things, that no\npaths going upwards from any non-epoll file with a length of more than 5\nedges exist. However, this check does not apply to non-epoll files.\n\nAs a result, it is possible to recurse to a depth of at least roughly 500,\ntested on v6.15. (I am unsure if deeper recursion is possible; and this may\nhave changed with commit 8c44dac8add7 (\"eventpoll: Fix priority inversion\nproblem\").)\n\nTo fix it:\n\n1. In ep_loop_check_proc(), note the subtree depth of each visited node,\nand use subtree depths for the total depth calculation even when a subtree\nhas already been visited.\n2. Add ep_get_upwards_depth_proc() for similarly determining the maximum\ndepth of an upwards walk.\n3. In ep_loop_check(), use these values to limit the total path length\nbetween epoll nodes to EP_MAX_NESTS edges.",
  "id": "GHSA-grcg-mgx8-mfvf",
  "modified": "2025-11-03T18:31:34Z",
  "published": "2025-08-19T18:31:34Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2025-38614"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/1b13b033062824495554e836a1ff5f85ccf6b039"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/2a0c0c974bea9619c6f41794775ae4b97530e0e6"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/3542c90797bc3ab83ebab54b737d751cf3682036"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/71379495ab70eaba19224bd71b5b9b399eb85e04"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/7a2125962c42d5336ca0495a9ce4cb38a63e9161"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/ea5f97dbdcb1651581a22bd10afd2f0dd9dc11d6"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/f2e467a48287c868818085aa35389a224d226732"
    },
    {
      "type": "WEB",
      "url": "https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html"
    }
  ],
  "schema_version": "1.4.0",
  "severity": []
}


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