# CVE-2026-64064: netfs: Fix netfs_invalidate_folio() to clear dirty bit if all changes gone

> A null pointer dereference in the Linux kernel netfs subsystem can cause a system crash when specific file operations are performed with caching disabled.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 19 Jul 2026
- **Updated:** 19 Jul 2026
- **Also known as:** BELL-CVE-2026-64064, DEBIAN-CVE-2026-64064, GHSA-gxmr-cf3v-qq46, UBUNTU-CVE-2026-64064

## What is CVE-2026-64064?

CVE-2026-64064 is a medium-severity vulnerability in Linux kernel, published on 19 Jul 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

netfs: Fix netfs_invalidate_folio() to clear dirty bit if all changes gone

If a streaming write is made, this will leave the relevant modified folio
in a not-uptodate, but dirty state with a netfs_folio struct hung off of
folio->private indicating the dirty range.  Subsequently truncating the
file such that the dirty data in the folio is removed, but the first part
of the folio theoretically remains will cause the netfs_folio struct to be
discarded... but will leave the dirty flag set.

If the folio is then read via mmap(), netfs_read_folio() will see that the
page is dirty and jump to netfs_read_gaps() to fill in the missing bits.
netfs_read_gaps(), however, expects there to be a netfs_folio struct
present and can oops because truncate removed it.

Fix this by calling folio_cancel_dirty() in netfs_invalidate_folio() in the
event that all the dirty data in the folio is erased (as nfs does).

Also add some tracepoints to log modifications to a dirty page.

This can be reproduced with something like:

    dd if=/dev/zero of=/xfstest.test/foo bs=1M count=1
    umount /xfstest.test
    mount /xfstest.test
    xfs_io -c "w 0xbbbf 0xf96c" \
           -c "truncate 0xbbbf" \
           -c "mmap -r 0xb000 0x11000" \
           -c "mr 0xb000 0x11000" \
           /xfstest.test/foo

with fscaching disabled (otherwise streaming writes are suppressed) and a
change to netfs_perform_write() to disallow streaming writes if the fd is
open O_RDWR:

	if (//(file->f_mode & FMODE_READ) || <--- comment this out
	    netfs_is_cache_enabled(ctx)) {

It should be reproducible even without this change, but if prevents the
above trivial xfs_io command from reproducing it.

Note that the initial dd is important: the file must start out sufficiently
large that the zero-point logic doesn't just clear the gaps because it
knows there's nothing in the file to read yet.  Unmounting and mounting is
needed to clear the pagecache (there are other ways to do that that may
also work).

This was initially reproduced with the generic/522 xfstest on some patches
that remove the FMODE_READ restriction.

## Which versions are affected by CVE-2026-64064?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-64064?

Apply the vendor's patch.

## Is CVE-2026-64064 being exploited?

There is no known exploitation of CVE-2026-64064 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-64064 and fix it if it is affected.

What it is: CVE-2026-64064 is a medium-severity vulnerability in Linux kernel, published on 19 Jul 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-64064 in the wild and no public exploit code.

Affected product: Linux kernel. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-64064/ (Markdown: https://insights.sbomify.com/CVE-2026-64064/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-64064
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-64064
- OSV: https://osv.dev/vulnerability/CVE-2026-64064

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-64064/
Summaries are generated and may contain mistakes; the official description above is the record.