CVE-2026-89704nfsd: sample writeback error cursor before async COPY loop

Description

In the Linux kernel, the following vulnerability has been resolved: nfsd: sample writeback error cursor before async COPY loop _nfsd_copy_file_range() samples dst->f_wb_err into "since" after the copy loop, then uses it to detect writeback errors via filemap_check_wb_err() once vfs_fsync_range() returns. Because the nfsd_file cache reuses a single struct file across requests targeting the same inode, a concurrent COMMIT or stable WRITE on dst advances dst->f_wb_err to the current mapping->wb_err via file_check_and_advance_wb_err() during its own vfs_fsync_range(). If that advancement lands between the writeback error appearing in mapping->wb_err and the COPY worker sampling "since", the worker captures the already-advanced cursor, errseq_check() sees cur == since and returns zero, and NFSD4_COPY_F_COMMITTED is set even though writeback failed. CB_OFFLOAD then encodes wr_stable_how = FILE_SYNC4, the client treats the copied data as durable, and the failure becomes silent data loss. Sample since once at the start of the function. The cursor then reflects state in effect before this COPY issues any writes, and filemap_check_wb_err() detects any error that occurs during the copy regardless of which thread first observes it. This matches the pattern used by nfsd_vfs_write() and nfsd4_clone_file_range().

Timeline

Scores

EPSS (exploitation in 30 days)

0.53% · top 55% of all CVEs (12 Nov 2026)

The list uses the assigner's score when there is one, then CISA's, then NVD's: High 7.5.

Affected products

• Linux · Linux

  • affected f14816f2f928c560d28ba344af689f56efcd6f55 – < 435e4246c7dfff2fbd76dfdbf91975d5d9f788c9
  • affected 3145fe0ebb16e1715ad541a301bc6675c8375fcd – < 9f539a1c0791f907eb4e6d04b43178d9962e2def
  • affected 555dbf1a9aac6d3150c8b52fa35f768a692f4eeb – < 4728504c021656128a07f4693af80ed4a5fcc863
  • affected 555dbf1a9aac6d3150c8b52fa35f768a692f4eeb – < 322422d66d1a04434a0dcc0c9d3a4c4b3f225117
  • affected 555dbf1a9aac6d3150c8b52fa35f768a692f4eeb – < 52b2db7a72e19ac2686fa4b2a52406661e7bf9e2
  • affected 555dbf1a9aac6d3150c8b52fa35f768a692f4eeb – < 8277d4a11ae2cb5495842be558fd946032c24363
  • affected 555dbf1a9aac6d3150c8b52fa35f768a692f4eeb – < a1cbafe756cd5e6ab0e099062f37da7a5b081169
  • affected 555dbf1a9aac6d3150c8b52fa35f768a692f4eeb – < 20a67a7d18221af736f124770c2c5e859b479046
  • affected 5.10.124 – < 5.10.270
  • affected 5.15.49 – < 5.15.221

• Linux · Linux

  • affected 5.17
  • unaffected < 5.17
  • unaffected 5.10.270 – ≤ 5.10.*
  • unaffected 5.15.221 – ≤ 5.15.*
  • unaffected 6.1.188 – ≤ 6.1.*
  • unaffected 6.6.157 – ≤ 6.6.*
  • unaffected 6.12.109 – ≤ 6.12.*
  • unaffected 6.18.50 – ≤ 6.18.*
  • unaffected 7.2.4 – ≤ 7.2.*
  • unaffected 7.3 – ≤ *

Sources

The same CVE in the primary databases and aggregators, to check against.

• CVE.org record (opens in a new tab)
• CVE List JSON (GitHub) (opens in a new tab)
• NVD (opens in a new tab)
• FIRST EPSS (opens in a new tab)
• EUVD EUVD-2026-76616 (opens in a new tab)
• OSV.dev (opens in a new tab)
• GitHub Advisories (opens in a new tab)
• CIRCL Vulnerability-Lookup (opens in a new tab)

Badge for a README or a ticket

[![CVE-2026-89704](https://cveledger.app/badge/CVE-2026-89704.svg)](https://cveledger.app/cve/CVE-2026-89704)

Record last updated 19 Oct 2026, 08:51 UTC.