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

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 include 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 Linux Kernel Out-of-Bounds Write Exploited High 8.8
• CVE-2013-6282 Linux Kernel Improper Input Validation Exploited High 8.8
• CVE-2022-0185 Linux Kernel Heap-Based Buffer Overflow Exploited High 8.4
• CVE-2013-2094 Linux Kernel Privilege Escalation Exploited High 8.4
• CVE-2026-53362 Linux Kernel Unspecified Exploited High 7.8

All Linux kernel vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as BELL-CVE-2026-64064, DEBIAN-CVE-2026-64064, GHSA-gxmr-cf3v-qq46, UBUNTU-CVE-2026-64064.