CVE-2024-26696

In the Linux kernel, the following vulnerability has been resolved: nilfs2:
fix hang in nilfs_lookup_dirty_data_buffers() Syzbot reported a hang issue
in migrate_pages_batch() called by mbind() and
nilfs_lookup_dirty_data_buffers() called in the log writer of nilfs2. While
migrate_pages_batch() locks a folio and waits for the writeback to
complete, the log writer thread that should bring the writeback to
completion picks up the folio being written back in
nilfs_lookup_dirty_data_buffers() that it calls for subsequent log creation
and was trying to lock the folio. Thus causing a deadlock. In the first
place, it is unexpected that folios/pages in the middle of writeback will
be updated and become dirty. Nilfs2 adds a checksum to verify the validity
of the log being written and uses it for recovery at mount, so data changes
during writeback are suppressed. Since this is broken, an unclean shutdown
could potentially cause recovery to fail. Investigation revealed that the
root cause is that the wait for writeback completion in
nilfs_page_mkwrite() is conditional, and if the backing device does not
require stable writes, data may be modified without waiting. Fix these
issues by making nilfs_page_mkwrite() wait for writeback to finish
regardless of the stable write requirement of the backing device.