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.

Weakness

The product does not properly acquire or release a lock on a resource, leading to unexpected resource state changes and behaviors.

Affected Software

Extended Description

Locking is a type of synchronization behavior that ensures that multiple independently-operating processes or threads do not interfere with each other when accessing the same resource. All processes/threads are expected to follow the same steps for locking. If these steps are not followed precisely - or if no locking is done at all - then another process/thread could modify the shared resource in a way that is not visible or predictable to the original process. This can lead to data or memory corruption, denial of service, etc.

Potential Mitigations

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/25.html
• https://cwe.mitre.org/data/definitions/26.html
• https://cwe.mitre.org/data/definitions/27.html

References

• https://git.kernel.org/stable/c/228742b2ddfb99dfd71e5a307e6088ab6836272e
• https://git.kernel.org/stable/c/38296afe3c6ee07319e01bb249aa4bb47c07b534
• https://git.kernel.org/stable/c/7e9b622bd0748cc104d66535b76d9b3535f9dc0f
• https://git.kernel.org/stable/c/8494ba2c9ea00a54d5b50e69b22c55a8958bce32
• https://git.kernel.org/stable/c/862ee4422c38be5c249844a684b00d0dbe9d1e46
• https://git.kernel.org/stable/c/98a4026b22ff440c7f47056481bcbbe442f607d6
• https://git.kernel.org/stable/c/e38585401d464578d30f5868ff4ca54475c34f7d
• https://git.kernel.org/stable/c/ea5ddbc11613b55e5128c85f57b08f907abd9b28
• https://git.kernel.org/stable/c/228742b2ddfb99dfd71e5a307e6088ab6836272e
• https://git.kernel.org/stable/c/38296afe3c6ee07319e01bb249aa4bb47c07b534
• https://git.kernel.org/stable/c/7e9b622bd0748cc104d66535b76d9b3535f9dc0f
• https://git.kernel.org/stable/c/8494ba2c9ea00a54d5b50e69b22c55a8958bce32
• https://git.kernel.org/stable/c/862ee4422c38be5c249844a684b00d0dbe9d1e46
• https://git.kernel.org/stable/c/98a4026b22ff440c7f47056481bcbbe442f607d6
• https://git.kernel.org/stable/c/e38585401d464578d30f5868ff4ca54475c34f7d
• https://git.kernel.org/stable/c/ea5ddbc11613b55e5128c85f57b08f907abd9b28
• https://lists.debian.org/debian-lts-announce/2024/06/msg00017.html
• https://lists.debian.org/debian-lts-announce/2024/06/msg00020.html