From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: linux-cve-announce@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@kernel.org>
Subject: CVE-2026-89704: nfsd: sample writeback error cursor before async COPY loop
Date: Fri, 11 Sep 2026 21:46:33 +0200 [thread overview]
Message-ID: <2026091156-CVE-2026-89704-414e@gregkh> (raw)
From: Greg Kroah-Hartman <gregkh@kernel.org>
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().
The Linux kernel CVE team has assigned CVE-2026-89704 to this issue.
Affected and fixed versions
===========================
Issue introduced in 5.17 with commit 555dbf1a9aac6d3150c8b52fa35f768a692f4eeb and fixed in 6.12.109 with commit 52b2db7a72e19ac2686fa4b2a52406661e7bf9e2
Issue introduced in 5.17 with commit 555dbf1a9aac6d3150c8b52fa35f768a692f4eeb and fixed in 6.18.50 with commit 8277d4a11ae2cb5495842be558fd946032c24363
Issue introduced in 5.17 with commit 555dbf1a9aac6d3150c8b52fa35f768a692f4eeb and fixed in 7.2.4 with commit a1cbafe756cd5e6ab0e099062f37da7a5b081169
Issue introduced in 5.17 with commit 555dbf1a9aac6d3150c8b52fa35f768a692f4eeb and fixed in 7.3-rc1 with commit 20a67a7d18221af736f124770c2c5e859b479046
Issue introduced in 5.10.124 with commit f14816f2f928c560d28ba344af689f56efcd6f55
Issue introduced in 5.15.49 with commit 3145fe0ebb16e1715ad541a301bc6675c8375fcd
Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.
Unaffected versions might change over time as fixes are backported to
older supported kernel versions. The official CVE entry at
https://cve.org/CVERecord/?id=CVE-2026-89704
will be updated if fixes are backported, please check that for the most
up to date information about this issue.
Affected files
==============
The file(s) affected by this issue are:
fs/nfsd/nfs4proc.c
Mitigation
==========
The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes. Individual
changes are never tested alone, but rather are part of a larger kernel
release. Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all. If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
https://git.kernel.org/stable/c/52b2db7a72e19ac2686fa4b2a52406661e7bf9e2
https://git.kernel.org/stable/c/8277d4a11ae2cb5495842be558fd946032c24363
https://git.kernel.org/stable/c/a1cbafe756cd5e6ab0e099062f37da7a5b081169
https://git.kernel.org/stable/c/20a67a7d18221af736f124770c2c5e859b479046
reply other threads:[~2026-09-11 20:05 UTC|newest]
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