Linux Kernel Netfs Zero Point Update Vulnerability

A vulnerability in the Linux kernel's netfs component affects the handling of the zero point update during the release of folios. This issue arises when there is uncommitted data in the page cache beyond the folio being released, but the on-server end-of-file (EOF) is within that folio. In such cases, the update incorrectly relies on the local file size, rather than the remote size tracked by the server. This vulnerability can lead to read gaps, where the system prematurely hits EOF, causing short reads. The issue was discovered using the fsx test tool, specifically with the CIFS file system and default caching options.

Impact

Exploitation of this vulnerability causes read gaps in the file system, where the expected data is not returned, leading to incomplete reads and potential data corruption.

Reproduction

The vulnerability can be reproduced by using the fsx test tool to write data beyond the folio being released, while the on-server EOF is within that folio. This can be done by truncating a file, writing data to specific offsets, and then mapping and reading the data, which will expose the read gaps if the vulnerability is present.

Remediation

Users can apply the latest patches available in the Linux kernel stable tree to address this vulnerability.