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

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

Severity

4

CVSS

(AV:L/AC:H/Au:S/C:N/I:N/A:C)

Published

07/30/2024

Created

09/07/2024

Added

09/06/2024

Modified

12/05/2024

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.

Solution(s)

• redhat-upgrade-kernel
• redhat-upgrade-kernel-rt

References

• CVE-2024-42102
• RHSA-2024:6267
• RHSA-2024:6268
• RHSA-2024:6567