Vulnerability CVE-2024-26696
Published: 2024-04-03

Description:
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.

 References:
https://git.kernel.org/stable/c/228742b2ddfb99dfd71e5a307e6088ab6836272e
https://git.kernel.org/stable/c/862ee4422c38be5c249844a684b00d0dbe9d1e46
https://git.kernel.org/stable/c/98a4026b22ff440c7f47056481bcbbe442f607d6
https://git.kernel.org/stable/c/7e9b622bd0748cc104d66535b76d9b3535f9dc0f
https://git.kernel.org/stable/c/8494ba2c9ea00a54d5b50e69b22c55a8958bce32
https://git.kernel.org/stable/c/ea5ddbc11613b55e5128c85f57b08f907abd9b28
https://git.kernel.org/stable/c/e38585401d464578d30f5868ff4ca54475c34f7d
https://git.kernel.org/stable/c/38296afe3c6ee07319e01bb249aa4bb47c07b534
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