ext4: clear stale xarray tags on folios skipped during writeback (CVE-2026-92502) | HOL Guard CVE

Unknown severity · Source severity not reportedCVE-2026-92502

ext4: clear stale xarray tags on folios skipped during writeback

Answer in brief

CVE-2026-92502 records a Unknown severity vulnerability in ext4: clear stale xarray tags on folios skipped during writeback. The current sources do not mark it as known exploited. The current feed maps Linux/Linux (generic), Linux/Linux (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Sep 17, 2026Updated Sep 17, 2026Source checked Sep 17, 2026First seen by HOL Sep 17, 2026Material review Sep 17, 2026

Upstream Advisory

Key facts

Risk: Unknown severitySource severity not reported
Exploitation: Not marked as known exploited
Affected software: 2 mapped packages or products
Fix availability: Available

Why this deserves its current priority

A CVSS score is not reported in the current record. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps Linux/Linux (generic), Linux/Linux (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
Linux/Linuxgeneric	>=dff4ac75eeeefc4397fe7cf8ce559425bf46b1f7 <f82a4929d0ef7ddf254c1c295ec1dfd24094f2de \|\| >=dff4ac75eeeefc4397fe7cf8ce559425bf46b1f7 <a450ab88bfd57b227d72c7a3faad54d16c3fc099 \|\| >=dff4ac75eeeefc4397fe7cf8ce559425bf46b1f7 <aa0042630b1f7cab735b0a168539281198822586 \|\| >=dff4ac75eeeefc4397fe7cf8ce559425bf46b1f7 <43ae387c3ae6a11227d096669ddf883e27a39a11 \|\| >=dff4ac75eeeefc4397fe7cf8ce559425bf46b1f7 <ec524aae479b4b2078c47492b90ec21200bce434	f82a4929d0ef7ddf254c1c295ec1dfd24094f2de, a450ab88bfd57b227d72c7a3faad54d16c3fc099, aa0042630b1f7cab735b0a168539281198822586, 43ae387c3ae6a11227d096669ddf883e27a39a11, ec524aae479b4b2078c47492b90ec21200bce434
Linux/Linuxgeneric	6.2	Not reported

Recommended response

Check inventory. Check lockfiles and deployed manifests for Linux/Linux, Linux/Linux.
Review the reported fix. Update Linux/Linux to f82a4929d0ef7ddf254c1c295ec1dfd24094f2de if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Sep 17, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Sep 17, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Sep 17, 2026

Sources and claim methodology

Upstream source description

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.

Quoted source text, attributed separately from HOL analysis.