{
  "affected": [
    {
      "ecosystem_specific": {
        "urgency": "not yet assigned"
      },
      "package": {
        "ecosystem": "Debian:13",
        "name": "linux"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "ecosystem_specific": {
        "urgency": "not yet assigned"
      },
      "package": {
        "ecosystem": "Debian:14",
        "name": "linux"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "details": "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); \tcontinue  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.",
  "id": "DEBIAN-CVE-2026-92502",
  "modified": "2026-09-18T04:47:33.001752918Z",
  "published": "2026-09-17T17:17:52.680Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://security-tracker.debian.org/tracker/CVE-2026-92502"
    }
  ],
  "upstream": [
    "CVE-2026-92502"
  ]
}