GHSA-2CVF-73CF-JRW5

Vulnerability from github – Published: 2025-10-22 15:31 – Updated: 2025-10-22 15:31
VLAI?
Details

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

posix-timers: Ensure timer ID search-loop limit is valid

posix_timer_add() tries to allocate a posix timer ID by starting from the cached ID which was stored by the last successful allocation.

This is done in a loop searching the ID space for a free slot one by one. The loop has to terminate when the search wrapped around to the starting point.

But that's racy vs. establishing the starting point. That is read out lockless, which leads to the following problem:

CPU0 CPU1 posix_timer_add() start = sig->posix_timer_id; lock(hash_lock); ... posix_timer_add() if (++sig->posix_timer_id < 0) start = sig->posix_timer_id; sig->posix_timer_id = 0;

So CPU1 can observe a negative start value, i.e. -1, and the loop break never happens because the condition can never be true:

if (sig->posix_timer_id == start) break;

While this is unlikely to ever turn into an endless loop as the ID space is huge (INT_MAX), the racy read of the start value caught the attention of KCSAN and Dmitry unearthed that incorrectness.

Rewrite it so that all id operations are under the hash lock.

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{
  "affected": [],
  "aliases": [
    "CVE-2023-53728"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2025-10-22T14:15:48Z",
    "severity": null
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nposix-timers: Ensure timer ID search-loop limit is valid\n\nposix_timer_add() tries to allocate a posix timer ID by starting from the\ncached ID which was stored by the last successful allocation.\n\nThis is done in a loop searching the ID space for a free slot one by\none. The loop has to terminate when the search wrapped around to the\nstarting point.\n\nBut that\u0027s racy vs. establishing the starting point. That is read out\nlockless, which leads to the following problem:\n\nCPU0\t  \t      \t     \t   CPU1\nposix_timer_add()\n  start = sig-\u003eposix_timer_id;\n  lock(hash_lock);\n  ...\t\t\t\t   posix_timer_add()\n  if (++sig-\u003eposix_timer_id \u003c 0)\n      \t\t\t             start = sig-\u003eposix_timer_id;\n     sig-\u003eposix_timer_id = 0;\n\nSo CPU1 can observe a negative start value, i.e. -1, and the loop break\nnever happens because the condition can never be true:\n\n  if (sig-\u003eposix_timer_id == start)\n     break;\n\nWhile this is unlikely to ever turn into an endless loop as the ID space is\nhuge (INT_MAX), the racy read of the start value caught the attention of\nKCSAN and Dmitry unearthed that incorrectness.\n\nRewrite it so that all id operations are under the hash lock.",
  "id": "GHSA-2cvf-73cf-jrw5",
  "modified": "2025-10-22T15:31:12Z",
  "published": "2025-10-22T15:31:12Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2023-53728"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/322377cc909defcca9451487484845e7e1d20d1b"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/37175e25edf7cc0d5a2cd2c2a1cbe2dcbf4a1937"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/6a0ac84501b4fec73a1a823c55cf13584c43f418"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/8ad6679a5bb97cdb3e14942729292b4bfcc0e223"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/8ce8849dd1e78dadcee0ec9acbd259d239b7069f"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/8dc52c200b889bc1cb34288fbf623d4ff381d2ae"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/9ea26a8494a0a9337e7415eafd6f3ed940327dc5"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/ef535e0315afd098c4beb1da364847eca4b56a20"
    }
  ],
  "schema_version": "1.4.0",
  "severity": []
}


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