# CVE-2026-31437

> Vulnerability.

## Description

In 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.

## Key facts

- **CVE ID:** CVE-2026-31437
- **Published:** 2026-04-22

## Primary sources

- NIST NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-31437

## Citation

> AI Analytics. CVE-2026-31437. Retrieved 2026-07-20 from https://api.ai-analytics.org/cve/CVE-2026-31437. Derived from NIST NVD. Licensed CC0.

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