CVE-2024-26630

In the Linux kernel, the following vulnerability has been resolved:

mm: cachestat: fix folio read-after-free in cache walk

In cachestat, we access the folio from the page caches xarray to compute its page offset, and check for its dirty and writeback flags. However, we do not hold a reference to the folio before performing these actions, which means the folio can concurrently be released and reused as another folio/page/slab.

Get around this altogether by just using xarrays existing machinery for the folio page offsets and dirty/writeback states.

This changes behavior for tmpfs files to now always report zeroes in their dirty and writeback counters. This is okay as tmpfs doesnt follow conventional writeback cache behavior: its pages get cleaned during swapout, after which theyre no longer resident etc.

Weakness

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory “belongs” to the code that operates on the new pointer.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/3a75cb05d53f4a6823a32deb078de1366954a804
• https://git.kernel.org/stable/c/ba60fdf75e89ea762bb617be578dc47f27655117
• https://git.kernel.org/stable/c/fe7e008e0ce728252e4ec652cceebcc62211657c
• https://git.kernel.org/stable/c/3a75cb05d53f4a6823a32deb078de1366954a804
• https://git.kernel.org/stable/c/ba60fdf75e89ea762bb617be578dc47f27655117
• https://git.kernel.org/stable/c/fe7e008e0ce728252e4ec652cceebcc62211657c