CVE-2024-42316 Information

Description

In the Linux kernel the following vulnerability has been resolved:

mm/mglru: fix div-by-zero in vmpressure_calc_level()

evict_folios() uses a second pass to reclaim folios that have gone through page writeback and become clean before it finishes the first pass since folio_rotate_reclaimable() cannot handle those folios due to the isolation.

The second pass tries to avoid potential double counting by deducting scan_control->nr_scanned. However this can result in underflow of nr_scanned under a condition where shrink_folio_list() does not increment nr_scanned i.e. when folio_trylock() fails.

The underflow can cause the divisor i.e. scale=scanned+reclaimed in vmpressure_calc_level() to become zero resulting in the following crash:

[exception RIP: vmpressure_work_fn+101] process_one_work at ffffffffa3313f2b

Since scan_control->nr_scanned has no established semantics the potential double counting has minimal risks. Therefore fix the problem by not deducting scan_control->nr_scanned in evict_folios().

Reference

https://git.kernel.org/stable/c/8de7bf77f21068a5f602bb1e59adbc5ab533509d https://git.kernel.org/stable/c/d6510f234c7d117790397f9bb150816b0a954a04 https://git.kernel.org/stable/c/a39e38be632f0e1c908d70d1c9cd071c03faf895 https://git.kernel.org/stable/c/8b671fe1a879923ecfb72dda6caf01460dd885ef