CVE-2025-38338 (GCVE-0-2025-38338)
Vulnerability from cvelistv5
Published
2025-07-10 08:15
Modified
2025-07-28 04:19
Severity ?
Summary
In the Linux kernel, the following vulnerability has been resolved: fs/nfs/read: fix double-unlock bug in nfs_return_empty_folio() Sometimes, when a file was read while it was being truncated by another NFS client, the kernel could deadlock because folio_unlock() was called twice, and the second call would XOR back the `PG_locked` flag. Most of the time (depending on the timing of the truncation), nobody notices the problem because folio_unlock() gets called three times, which flips `PG_locked` back off: 1. vfs_read, nfs_read_folio, ... nfs_read_add_folio, nfs_return_empty_folio 2. vfs_read, nfs_read_folio, ... netfs_read_collection, netfs_unlock_abandoned_read_pages 3. vfs_read, ... nfs_do_read_folio, nfs_read_add_folio, nfs_return_empty_folio The problem is that nfs_read_add_folio() is not supposed to unlock the folio if fscache is enabled, and a nfs_netfs_folio_unlock() check is missing in nfs_return_empty_folio(). Rarely this leads to a warning in netfs_read_collection(): ------------[ cut here ]------------ R=0000031c: folio 10 is not locked WARNING: CPU: 0 PID: 29 at fs/netfs/read_collect.c:133 netfs_read_collection+0x7c0/0xf00 [...] Workqueue: events_unbound netfs_read_collection_worker RIP: 0010:netfs_read_collection+0x7c0/0xf00 [...] Call Trace: <TASK> netfs_read_collection_worker+0x67/0x80 process_one_work+0x12e/0x2c0 worker_thread+0x295/0x3a0 Most of the time, however, processes just get stuck forever in folio_wait_bit_common(), waiting for `PG_locked` to disappear, which never happens because nobody is really holding the folio lock.
References
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/14f5549ad163be2c018abc1bb38370fff617a243
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/1e93b61d3eaa14bfebcc2716ac09d43f3845d420
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/4c10fa44bc5f700e2ea21de2fbae520ba21f19d9
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/5bf0b9eeb0174686f22c2e5b8fb9f47ad25da6f5
Impacted products
Vendor Product Version
Linux Linux Version: 000dbe0bec058cbf2ca9e156e4a5584f5158b0f9
Version: 000dbe0bec058cbf2ca9e156e4a5584f5158b0f9
Version: 000dbe0bec058cbf2ca9e156e4a5584f5158b0f9
Version: 000dbe0bec058cbf2ca9e156e4a5584f5158b0f9
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   Linux Linux Version: 6.4
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{
  "containers": {
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      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/nfs/read.c"
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              "version": "6.6.95",
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              "version": "6.12.35",
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              "version": "6.15.4",
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nfs/nfs/read: fix double-unlock bug in nfs_return_empty_folio()\n\nSometimes, when a file was read while it was being truncated by\nanother NFS client, the kernel could deadlock because folio_unlock()\nwas called twice, and the second call would XOR back the `PG_locked`\nflag.\n\nMost of the time (depending on the timing of the truncation), nobody\nnotices the problem because folio_unlock() gets called three times,\nwhich flips `PG_locked` back off:\n\n 1. vfs_read, nfs_read_folio, ... nfs_read_add_folio,\n    nfs_return_empty_folio\n 2. vfs_read, nfs_read_folio, ... netfs_read_collection,\n    netfs_unlock_abandoned_read_pages\n 3. vfs_read, ... nfs_do_read_folio, nfs_read_add_folio,\n    nfs_return_empty_folio\n\nThe problem is that nfs_read_add_folio() is not supposed to unlock the\nfolio if fscache is enabled, and a nfs_netfs_folio_unlock() check is\nmissing in nfs_return_empty_folio().\n\nRarely this leads to a warning in netfs_read_collection():\n\n ------------[ cut here ]------------\n R=0000031c: folio 10 is not locked\n WARNING: CPU: 0 PID: 29 at fs/netfs/read_collect.c:133 netfs_read_collection+0x7c0/0xf00\n [...]\n Workqueue: events_unbound netfs_read_collection_worker\n RIP: 0010:netfs_read_collection+0x7c0/0xf00\n [...]\n Call Trace:\n  \u003cTASK\u003e\n  netfs_read_collection_worker+0x67/0x80\n  process_one_work+0x12e/0x2c0\n  worker_thread+0x295/0x3a0\n\nMost of the time, however, processes just get stuck forever in\nfolio_wait_bit_common(), waiting for `PG_locked` to disappear, which\nnever happens because nobody is really holding the folio lock."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2025-07-28T04:19:20.008Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
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          "url": "https://git.kernel.org/stable/c/14f5549ad163be2c018abc1bb38370fff617a243"
        },
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          "url": "https://git.kernel.org/stable/c/5bf0b9eeb0174686f22c2e5b8fb9f47ad25da6f5"
        },
        {
          "url": "https://git.kernel.org/stable/c/1e93b61d3eaa14bfebcc2716ac09d43f3845d420"
        },
        {
          "url": "https://git.kernel.org/stable/c/4c10fa44bc5f700e2ea21de2fbae520ba21f19d9"
        }
      ],
      "title": "fs/nfs/read: fix double-unlock bug in nfs_return_empty_folio()",
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        "engine": "bippy-1.2.0"
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  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2025-38338",
    "datePublished": "2025-07-10T08:15:09.022Z",
    "dateReserved": "2025-04-16T04:51:24.005Z",
    "dateUpdated": "2025-07-28T04:19:20.008Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.1",
  "vulnerability-lookup:meta": {
    "nvd": "{\"cve\":{\"id\":\"CVE-2025-38338\",\"sourceIdentifier\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"published\":\"2025-07-10T09:15:28.510\",\"lastModified\":\"2025-07-10T13:17:30.017\",\"vulnStatus\":\"Awaiting Analysis\",\"cveTags\":[],\"descriptions\":[{\"lang\":\"en\",\"value\":\"In the Linux kernel, the following vulnerability has been resolved:\\n\\nfs/nfs/read: fix double-unlock bug in nfs_return_empty_folio()\\n\\nSometimes, when a file was read while it was being truncated by\\nanother NFS client, the kernel could deadlock because folio_unlock()\\nwas called twice, and the second call would XOR back the `PG_locked`\\nflag.\\n\\nMost of the time (depending on the timing of the truncation), nobody\\nnotices the problem because folio_unlock() gets called three times,\\nwhich flips `PG_locked` back off:\\n\\n 1. vfs_read, nfs_read_folio, ... nfs_read_add_folio,\\n    nfs_return_empty_folio\\n 2. vfs_read, nfs_read_folio, ... netfs_read_collection,\\n    netfs_unlock_abandoned_read_pages\\n 3. vfs_read, ... nfs_do_read_folio, nfs_read_add_folio,\\n    nfs_return_empty_folio\\n\\nThe problem is that nfs_read_add_folio() is not supposed to unlock the\\nfolio if fscache is enabled, and a nfs_netfs_folio_unlock() check is\\nmissing in nfs_return_empty_folio().\\n\\nRarely this leads to a warning in netfs_read_collection():\\n\\n ------------[ cut here ]------------\\n R=0000031c: folio 10 is not locked\\n WARNING: CPU: 0 PID: 29 at fs/netfs/read_collect.c:133 netfs_read_collection+0x7c0/0xf00\\n [...]\\n Workqueue: events_unbound netfs_read_collection_worker\\n RIP: 0010:netfs_read_collection+0x7c0/0xf00\\n [...]\\n Call Trace:\\n  \u003cTASK\u003e\\n  netfs_read_collection_worker+0x67/0x80\\n  process_one_work+0x12e/0x2c0\\n  worker_thread+0x295/0x3a0\\n\\nMost of the time, however, processes just get stuck forever in\\nfolio_wait_bit_common(), waiting for `PG_locked` to disappear, which\\nnever happens because nobody is really holding the folio lock.\"}],\"metrics\":{},\"references\":[{\"url\":\"https://git.kernel.org/stable/c/14f5549ad163be2c018abc1bb38370fff617a243\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/1e93b61d3eaa14bfebcc2716ac09d43f3845d420\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/4c10fa44bc5f700e2ea21de2fbae520ba21f19d9\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/5bf0b9eeb0174686f22c2e5b8fb9f47ad25da6f5\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"}]}}"
  }
}


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