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

Affected: Linux

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…

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