{
  "schema_version": "1.6.1",
  "id": "RPI-CVE-2025-40214",
  "modified": "2026-10-07T17:22:01Z",
  "upstream": [
    "CVE-2025-40214"
  ],
  "published": "2025-12-04T12:38:44Z",
  "summary": "af_unix: Initialise scc_index in unix_add_edge().",
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\naf_unix: Initialise scc_index in unix_add_edge().\n\nQuang Le reported that the AF_UNIX GC could garbage-collect a\nreceive queue of an alive in-flight socket, with a nice repro.\n\nThe repro consists of three stages.\n\n  1)\n    1-a. Create a single cyclic reference with many sockets\n    1-b. close() all sockets\n    1-c. Trigger GC\n\n  2)\n    2-a. Pass sk-A to an embryo sk-B\n    2-b. Pass sk-X to sk-X\n    2-c. Trigger GC\n\n  3)\n    3-a. accept() the embryo sk-B\n    3-b. Pass sk-B to sk-C\n    3-c. close() the in-flight sk-A\n    3-d. Trigger GC\n\nAs of 2-c, sk-A and sk-X are linked to unix_unvisited_vertices,\nand unix_walk_scc() groups them into two different SCCs:\n\n  unix_sk(sk-A)->vertex->scc_index = 2 (UNIX_VERTEX_INDEX_START)\n  unix_sk(sk-X)->vertex->scc_index = 3\n\nOnce GC completes, unix_graph_grouped is set to true.\nAlso, unix_graph_maybe_cyclic is set to true due to sk-X's\ncyclic self-reference, which makes close() trigger GC.\n\nAt 3-b, unix_add_edge() allocates unix_sk(sk-B)->vertex and\nlinks it to unix_unvisited_vertices.\n\nunix_update_graph() is called at 3-a. and 3-b., but neither\nunix_graph_grouped nor unix_graph_maybe_cyclic is changed\nbecause both sk-B's listener and sk-C are not in-flight.\n\n3-c decrements sk-A's file refcnt to 1.\n\nSince unix_graph_grouped is true at 3-d, unix_walk_scc_fast()\nis finally called and iterates 3 sockets sk-A, sk-B, and sk-X:\n\n  sk-A -> sk-B (-> sk-C)\n  sk-X -> sk-X\n\nThis is totally fine.  All of them are not yet close()d and\nshould be grouped into different SCCs.\n\nHowever, unix_vertex_dead() misjudges that sk-A and sk-B are\nin the same SCC and sk-A is dead.\n\n  unix_sk(sk-A)->scc_index == unix_sk(sk-B)->scc_index <-- Wrong!\n  &&\n  sk-A's file refcnt == unix_sk(sk-A)->vertex->out_degree\n                                       ^-- 1 in-flight count for sk-B\n  -> sk-A is dead !?\n\nThe problem is that unix_add_edge() does not initialise scc_index.\n\nStage 1) is used for heap spraying, making a newly allocated\nvertex have vertex->scc_index == 2 (UNIX_VERTEX_INDEX_START)\nset by unix_walk_scc() at 1-c.\n\nLet's track the max SCC index from the previous unix_walk_scc()\ncall and assign the max + 1 to a new vertex's scc_index.\n\nThis way, we can continue to avoid Tarjan's algorithm while\npreventing misjudgments.",
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  "references": [
    {
      "type": "ADVISORY",
      "url": "https://www.cve.org/CVERecord?id=CVE-2025-40214"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/20003fbb9174121b27bd1da6ebe61542ac4c327d"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/4cd8d755c7d4f515dd9abf483316aca2f1b7b0f3"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/db81ad20fd8aef7cc7d536c52ee5ea4c1f979128"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/1aa7e40ee850c9053e769957ce6541173891204d"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/60e6489f8e3b086bd1130ad4450a2c112e863791"
    }
  ],
  "database_specific": {
    "source": "https://git.kernel.org/pub/scm/linux/security/vulns.git",
    "upstream_modified": "2026-08-05T12:19:11Z"
  }
}