nfsd: fix partial-write detection in nfsd_direct_write
Summary
| CVE | CVE-2026-89678 |
|---|---|
| State | PUBLISHED |
| Assigner | Linux |
| Source Priority | CVE Program / NVD first with legacy fallback |
| Published | 2026-09-11 20:19:54 UTC |
| Updated | 2026-09-13 07:17:33 UTC |
| Description | In the Linux kernel, the following vulnerability has been resolved: nfsd: fix partial-write detection in nfsd_direct_write nfsd_direct_write() walks a list of write segments and, after each vfs_iocb_iter_write(), tries to detect a short write so the loop can stop before placing the next segment at a wrong file offset: host_err = vfs_iocb_iter_write(file, kiocb, &segments[i].iter); if (host_err < 0) return host_err; *cnt += host_err; if (host_err < segments[i].iter.count) break; /* partial write */ vfs_iocb_iter_write() runs the iter through ->write_iter(), which advances the iter by the number of bytes written. By the time the check runs, segments[i].iter.count is the residual, not the original request length: before write_iter: iter.count == original_len after write_iter: iter.count == original_len - host_err The condition then reduces to host_err < original_len - host_err, so the break fires only when less than half of the segment was written. Any short write completing between 50% and 99% of the segment slips through; the loop advances to the next segment with kiocb->ki_pos only bumped by the short amount, writing the next segment's payload at the wrong offset and over-reporting *cnt to the NFS client. Snapshot the segment's byte count before the write and compare host_err against that snapshot so any short write breaks the loop. |
Risk And Classification
Primary CVSS: v3.1 7.5 HIGH from 416baaa9-dc9f-4396-8d5f-8c081fb06d67
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
EPSS: 0.003540000 probability, percentile 0.287410000 (date 2026-09-14)
| Version | Source | Type | Score | Severity | Vector |
|---|---|---|---|---|---|
| 3.1 | 416baaa9-dc9f-4396-8d5f-8c081fb06d67 | Secondary | 7.5 | HIGH | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N |
| 3.1 | CNA | DECLARED | 7.5 | HIGH | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N |
CVSS v3.1 Breakdown
Attack Vector
NetworkAttack Complexity
LowPrivileges Required
NoneUser Interaction
NoneScope
UnchangedConfidentiality
NoneIntegrity
HighAvailability
NoneCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Vendor Declared Affected Products
| Source | Vendor | Product | Version | Platforms |
|---|---|---|---|---|
| CNA | Linux | Linux | affected 06c5c97293e3fca99ce15da157068edf45a7c6e4 fa6590dfd16ab55f03b658b079072ace3504825e git | Not specified |
| CNA | Linux | Linux | affected 06c5c97293e3fca99ce15da157068edf45a7c6e4 250ec14932d5cfe102f68a57892bb566eee7f83e git | Not specified |
| CNA | Linux | Linux | affected 6.19 | Not specified |
| CNA | Linux | Linux | unaffected 6.19 semver | Not specified |
| CNA | Linux | Linux | unaffected 7.2.4 7.2.* semver | Not specified |
| CNA | Linux | Linux | unaffected 7.3-rc1 * original_commit_for_fix | Not specified |
References
| Reference | Source | Link | Tags |
|---|---|---|---|
| git.kernel.org/stable/c/fa6590dfd16ab55f03b658b079072ace3504825e | 416baaa9-dc9f-4396-8d5f-8c081fb06d67 | git.kernel.org | |
| git.kernel.org/stable/c/250ec14932d5cfe102f68a57892bb566eee7f83e | 416baaa9-dc9f-4396-8d5f-8c081fb06d67 | git.kernel.org | |
| CVE Program record | CVE.ORG | www.cve.org | canonical |
| NVD vulnerability detail | NVD | nvd.nist.gov | canonical, analysis |
No vendor comments have been submitted for this CVE.
There are currently no legacy QID mappings associated with this CVE.