CVE-2024-42102: Revert "mm/writeback: fix possible divide-by-zero in wb_dirty_limits(), again"

Severity: medium (CVSS 4.7 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2024-07-30 · updated 2026-06-17
Weakness: CWE-369

Description

In the Linux kernel, the following vulnerability has been resolved: Revert "mm/writeback: fix possible divide-by-zero in wb_dirty_limits(), again" Patch series "mm: Avoid possible overflows in dirty throttling". Dirty throttling logic assumes dirty limits in page units fit into 32-bits. This patch series makes sure this is true (see patch 2/2 for more details). This patch (of 2): This reverts commit 9319b647902cbd5cc884ac08a8a6d54ce111fc78. The commit is broken in several ways. Firstly, the removed (u64) cast from the multiplication will introduce a multiplication overflow on 32-bit archs if wb_thresh * bg_thresh >= 1<<32 (which is actually common - the default settings with 4GB of RAM will trigger this). Secondly, the div64_u64() is unnecessarily expensive on 32-bit archs. We have div64_ul() in case we want to be safe & cheap. Thirdly, if dirty thresholds are larger than 1<<32 pages, then dirty balancing is going to blow up in many other spectacular ways anyway so trying to fix one possible overflow is just moot.

Affected products

Linux kernel: from 4.19.307 before 4.19.318; from 5.4.269 before 5.4.280; from 5.10.210 before 5.10.222; from 5.15.149 before 5.15.163; from 6.1.79 before 6.1.98; from 6.6.18 before 6.6.39 — fixed in 4.19.318, 5.10.222, 5.15.163, 5.4.280, 6.1.98, 6.6.39

How to fix

Upgrade to a fixed version: Linux kernel 4.19.318, 5.10.222, 5.15.163, 5.4.280. Check the vendor advisory for mitigations.

References

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