netfs: Fix NULL pointer dereference in netfs_unbuffered_write() on retry

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Summary

CVECVE-2026-31437
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-04-22 14:16:36 UTC
Updated2026-05-19 22:09:14 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: netfs: Fix NULL pointer dereference in netfs_unbuffered_write() on retry When a write subrequest is marked NETFS_SREQ_NEED_RETRY, the retry path in netfs_unbuffered_write() unconditionally calls stream->prepare_write() without checking if it is NULL. Filesystems such as 9P do not set the prepare_write operation, so stream->prepare_write remains NULL. When get_user_pages() fails with -EFAULT and the subrequest is flagged for retry, this results in a NULL pointer dereference at fs/netfs/direct_write.c:189. Fix this by mirroring the pattern already used in write_retry.c: if stream->prepare_write is NULL, skip renegotiation and directly reissue the subrequest via netfs_reissue_write(), which handles iterator reset, IN_PROGRESS flag, stats update and reissue internally.

Risk And Classification

Primary CVSS: v3.1 5.5 MEDIUM from [email protected]

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

EPSS: 0.000170000 probability, percentile 0.040700000 (date 2026-04-26)

Problem Types: CWE-476

CVSS v3.1 Breakdown

Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Operating System Linux Linux Kernel All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 72d08d2839649d1c5efbe375751f4473fa4486af a4d1b4ba9754bac3efebd06f583a44a7af52c0ab git Not specified
CNA Linux Linux affected 0c29f6d63122a0168d67cb8ecde5b4cf7fe4acb0 7a5482f5ce891decbf36f2e6fab1e9fc4a76a684 git Not specified
CNA Linux Linux affected a0b4c7a49137ed21279f354eb59f49ddae8dffc2 e9075e420a1eb3b52c60f3b95893a55e77419ce8 git Not specified
CNA Linux Linux affected 6.18.17 6.18.21 semver Not specified
CNA Linux Linux affected 6.19.7 6.19.11 semver Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/a4d1b4ba9754bac3efebd06f583a44a7af52c0ab 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/e9075e420a1eb3b52c60f3b95893a55e77419ce8 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/7a5482f5ce891decbf36f2e6fab1e9fc4a76a684 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
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