概要

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 into32-bits. This patch series makes sure this is true (see patch 2/2 formore details).This patch (of 2):This reverts commit 9319b647902cbd5cc884ac08a8a6d54ce111fc78.The commit is broken in several ways. Firstly, the removed (u64) castfrom the multiplication will introduce a multiplication overflow on 32-bitarchs if wb_thresh * bg_thresh &gt;= 1<<32 (which is actually common - thedefault settings with 4GB of RAM will trigger this). Secondly, thediv64_u64() is unnecessarily expensive on 32-bit archs. We havediv64_ul() in case we want to be safe &amp; cheap. Thirdly, if dirtythresholds are larger than 1<<32 pages, then dirty balancing is going toblow up in many other spectacular ways anyway so trying to fix onepossible overflow is just moot.

CVSS v3 指标

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