CVE-2026-92502 (GCVE-0-2026-92502)
Vulnerability from cvelistv5
Published
2026-09-17 16:10
Modified
2026-10-19 09:04
Severity ?
Summary
In the Linux kernel, the following vulnerability has been resolved: ext4: clear stale xarray tags on folios skipped during writeback In data=journal mode, the writeback thread can hit the WARN_ON_ONCE(sb_rdonly(sb)) in ext4_journal_check_start() while the superblock is being remounted read-only during reboot: Workqueue: writeback wb_workfn (flush-253:0) RIP: 0010:ext4_journal_check_start+0x8b/0xd0 Call Trace: __ext4_journal_start_sb+0x3c/0x1e0 mpage_prepare_extent_to_map+0x4af/0x580 ext4_do_writepages+0x3c0/0x1080 ext4_writepages+0xc8/0x1a0 do_writepages+0xc4/0x180 __writeback_single_inode+0x45/0x2f0 writeback_sb_inodes+0x26b/0x5d0 __writeback_inodes_wb+0x54/0x100 wb_writeback+0x1ac/0x320 wb_workfn+0x394/0x470 And followed by the warning: EXT4-fs warning (device vda1): ext4_evict_inode:195: inode #6263: comm (sd-umount): data will be lost This issue is not reproduced every time, but frequently. The reproduction step is to create a VM with 8 CPUs, 16G memory and setup data=journal: sudo tune2fs -o journal_data /dev/vda1 Run fio: rm -f fiotest fio --name=fiotest --rw=randwrite --bs=4k --runtime=6 --ioengine=libaio --iodepth=256 --numjobs=8 --filename=fiotest --filesize=30G --group_reporting Reboot the VM, and check the console output from: virsh console testvm But there is no dirty inode, folio_clear_dirty_for_io clears PG_dirty but leaves tags PAGECACHE_TAG_DIRTY and PAGECACHE_TAG_TOWRITE set which are only cleared by __folio_start_writeback. In data=journal mode, jbd2 checkpoints the journalled data to its final location and clears its own dirty flag without touching folio PG_dirty or xarray dirty flags. The commit f4a2b42e7891 ("ext4: fix stale xarray tags after writeback") fixes when PG_dirty is still set but there is no dirty page. Another case is PG_dirty is cleared, but PAGECACHE_TAG_DIRTY and PAGECACHE_TAG_TOWRITE is still set. In this case, writeback thread checks clean folio and skips it in mpage_prepare_extent_to_map: if (!folio_test_dirty(folio) || ... folio_unlcok(folio); continue And never reaches ext4_bio_write_folio where the commit f4a2b42e7891 clears the stale xarray tags. Print debug logs after the filesystem is remounted read-only: writepages RDONLY nrpages=2048 dirtytag=1 wbtag=0 towrite=1 sync=0 And all folios are actually clean: folio idx=3 dirty=0 wb=0 checked=0 dirtybuf=0 jbddirty=0 mapped=1 ... We need to clear the xarray stale tags for such clean folios by cycling them through writeback in the skip path, the same way f4a2b42e7891 does in ext4_bio_write_folio.
References
Impacted products
Vendor Product Version
Linux Linux Version: dff4ac75eeeefc4397fe7cf8ce559425bf46b1f7
Version: dff4ac75eeeefc4397fe7cf8ce559425bf46b1f7
Version: dff4ac75eeeefc4397fe7cf8ce559425bf46b1f7
Version: dff4ac75eeeefc4397fe7cf8ce559425bf46b1f7
Version: dff4ac75eeeefc4397fe7cf8ce559425bf46b1f7
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/ext4/inode.c"
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          "vendor": "Linux",
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              "status": "unaffected",
              "version": "7.3",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
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              "cpeMatch": [
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              "negate": false,
              "operator": "OR"
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          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\next4: clear stale xarray tags on folios skipped during writeback\n\nIn data=journal mode, the writeback thread can hit the\nWARN_ON_ONCE(sb_rdonly(sb)) in ext4_journal_check_start() while the\nsuperblock is being remounted read-only during reboot:\n\nWorkqueue: writeback wb_workfn (flush-253:0)\nRIP: 0010:ext4_journal_check_start+0x8b/0xd0\nCall Trace:\n  __ext4_journal_start_sb+0x3c/0x1e0\n  mpage_prepare_extent_to_map+0x4af/0x580\n  ext4_do_writepages+0x3c0/0x1080\n  ext4_writepages+0xc8/0x1a0\n  do_writepages+0xc4/0x180\n  __writeback_single_inode+0x45/0x2f0\n  writeback_sb_inodes+0x26b/0x5d0\n  __writeback_inodes_wb+0x54/0x100\n  wb_writeback+0x1ac/0x320\n  wb_workfn+0x394/0x470\n\nAnd followed by the warning:\nEXT4-fs warning (device vda1): ext4_evict_inode:195: inode #6263:\ncomm (sd-umount): data will be lost\n\nThis issue is not reproduced every time, but frequently.\nThe reproduction step is to create a VM with 8 CPUs, 16G memory and\nsetup data=journal:\nsudo tune2fs -o journal_data /dev/vda1\nRun fio:\nrm -f fiotest\nfio --name=fiotest --rw=randwrite --bs=4k --runtime=6 --ioengine=libaio\n--iodepth=256 --numjobs=8 --filename=fiotest --filesize=30G\n--group_reporting\nReboot the VM, and check the console output from:\nvirsh console testvm\n\nBut there is no dirty inode, folio_clear_dirty_for_io clears PG_dirty\nbut leaves tags PAGECACHE_TAG_DIRTY and PAGECACHE_TAG_TOWRITE set which\nare only cleared by __folio_start_writeback.\nIn data=journal mode, jbd2 checkpoints the journalled data to its final\nlocation and clears its own dirty flag without touching folio PG_dirty\nor xarray dirty flags.\nThe commit f4a2b42e7891 (\"ext4: fix stale xarray tags after writeback\")\nfixes when PG_dirty is still set but there is no dirty page.\nAnother case is PG_dirty is cleared, but PAGECACHE_TAG_DIRTY and\nPAGECACHE_TAG_TOWRITE is still set. In this case, writeback thread\nchecks clean folio and skips it in mpage_prepare_extent_to_map:\nif (!folio_test_dirty(folio) ||\n    ...\n        folio_unlcok(folio);\n\tcontinue\n\nAnd never reaches ext4_bio_write_folio where the commit f4a2b42e7891\nclears the stale xarray tags. Print debug logs after the filesystem\nis remounted read-only:\nwritepages RDONLY nrpages=2048 dirtytag=1 wbtag=0 towrite=1 sync=0\nAnd all folios are actually clean:\nfolio idx=3 dirty=0 wb=0 checked=0 dirtybuf=0 jbddirty=0 mapped=1\n...\n\nWe need to clear the xarray stale tags for such clean folios by\ncycling them through writeback in the skip path, the same way\nf4a2b42e7891 does in ext4_bio_write_folio."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-19T09:04:08.456Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/f82a4929d0ef7ddf254c1c295ec1dfd24094f2de"
        },
        {
          "url": "https://git.kernel.org/stable/c/a450ab88bfd57b227d72c7a3faad54d16c3fc099"
        },
        {
          "url": "https://git.kernel.org/stable/c/aa0042630b1f7cab735b0a168539281198822586"
        },
        {
          "url": "https://git.kernel.org/stable/c/43ae387c3ae6a11227d096669ddf883e27a39a11"
        },
        {
          "url": "https://git.kernel.org/stable/c/ec524aae479b4b2078c47492b90ec21200bce434"
        }
      ],
      "title": "ext4: clear stale xarray tags on folios skipped during writeback",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-92502",
    "datePublished": "2026-09-17T16:10:15.399Z",
    "dateReserved": "2026-09-16T12:21:13.872Z",
    "dateUpdated": "2026-10-19T09:04:08.456Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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