UBUNTU-CVE-2024-42102
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.
02 / AFFECTED SOFTWARE
Affected packages
11 explicit affected versions
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26 explicit affected versions
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44 explicit affected versions
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03 / CONNECTIONS
Connected vulnerabilities
04 / EVIDENCE
Source records
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.
05 / REFERENCES
Further evidence
- https://git.kernel.org/linus/30139c702048f1097342a31302cbd3d478f50c63
- https://git.kernel.org/stable/c/000099d71648504fb9c7a4616f92c2b70c3e44ec
- https://git.kernel.org/stable/c/145faa3d03688cbb7bbaaecbd84c01539852942c
- https://git.kernel.org/stable/c/23a28f5f3f6ca1e4184bd0e9631cd0944cf1c807
- https://git.kernel.org/stable/c/253f9ea7e8e53a5176bd80ceb174907b10724c1a
- https://git.kernel.org/stable/c/2820005edae13b140f2d54267d1bd6bb23915f59
- https://git.kernel.org/stable/c/30139c702048f1097342a31302cbd3d478f50c63
- https://git.kernel.org/stable/c/cbbe17a324437c0ff99881a3ee453da45b228a00
- https://git.kernel.org/stable/c/f6620df12cb6bdcad671d269debbb23573502f9d
- https://ubuntu.com/security/CVE-2024-42102
- https://ubuntu.com/security/notices/USN-7003-1
- https://ubuntu.com/security/notices/USN-7003-2
- https://ubuntu.com/security/notices/USN-7003-3
- https://ubuntu.com/security/notices/USN-7003-4
- https://ubuntu.com/security/notices/USN-7003-5
- https://ubuntu.com/security/notices/USN-7006-1
- https://ubuntu.com/security/notices/USN-7007-1
- https://ubuntu.com/security/notices/USN-7007-2
- https://ubuntu.com/security/notices/USN-7007-3
- https://ubuntu.com/security/notices/USN-7009-1
- https://ubuntu.com/security/notices/USN-7009-2
- https://ubuntu.com/security/notices/USN-7019-1
- https://ubuntu.com/security/notices/USN-7089-1
- https://ubuntu.com/security/notices/USN-7089-2
- https://ubuntu.com/security/notices/USN-7089-3
- https://ubuntu.com/security/notices/USN-7089-4
- https://ubuntu.com/security/notices/USN-7089-5
- https://ubuntu.com/security/notices/USN-7089-6
- https://ubuntu.com/security/notices/USN-7089-7
- https://ubuntu.com/security/notices/USN-7090-1
- https://ubuntu.com/security/notices/USN-7095-1
- https://ubuntu.com/security/notices/USN-7156-1
- https://www.cve.org/CVERecord?id=CVE-2024-42102