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Unity Linux 20.1070e Security Update: kernel (UTSA-2025-987239)

medium Nessus Plugin ID 269071

Synopsis

The Unity Linux host is missing one or more security updates.

Description

The Unity Linux 20 host has a package installed that is affected by a vulnerability as referenced in the UTSA-2025-987239 advisory.

 In the Linux kernel, the following vulnerability has been resolved:

 iocost: Fix divide-by-zero on donation from low hweight cgroup

 The donation calculation logic assumes that the donor has non-zero after-donation hweight, so the lowest active hweight a donating cgroup can have is 2 so that it can donate 1 while keeping the other 1 for itself.
 Earlier, we only donated from cgroups with sizable surpluses so this condition was always true. However, with the precise donation algorithm implemented, f1de2439ec43 (blk-iocost: revamp donation amount determination) made the donation amount calculation exact enabling even low hweight cgroups to donate.

 This means that in rare occasions, a cgroup with active hweight of 1 can enter donation calculation triggering the following warning and then a divide-by-zero oops.

 WARNING: CPU: 4 PID: 0 at block/blk-iocost.c:1928 transfer_surpluses.cold+0x0/0x53 [884/94867] ...
 RIP: 0010:transfer_surpluses.cold+0x0/0x53 Code: 92 ff 48 c7 c7 28 d1 ab b5 65 48 8b 34 25 00 ae 01 00 48 81 c6 90 06 00 00 e8 8b 3f fe ff 48 c7 c0 ea ff ff ff e9 95 ff 92 ff <0f> 0b 48 c7 c7 30 da ab b5 e8 71 3f fe ff 4c 89 e8 4d 85 ed 74 0 4 ...
 Call Trace:
 <IRQ> ioc_timer_fn+0x1043/0x1390 call_timer_fn+0xa1/0x2c0
 __run_timers.part.0+0x1ec/0x2e0 run_timer_softirq+0x35/0x70 ...
 iocg: invalid donation weights in /a/b: active=1 donating=1 after=0

 Fix it by excluding cgroups w/ active hweight < 2 from donating. Excluding these extreme low hweight donations shouldn't affect work conservation in any meaningful way.

Tenable has extracted the preceding description block directly from the Unity Linux security advisory.

Note that Nessus has not tested for this issue but has instead relied only on the application's self-reported version number.

Solution

Update the affected kernel package.

See Also

http://www.nessus.org/u?2a09a1da

http://www.nessus.org/u?ff8a5070

https://nvd.nist.gov/vuln/detail/CVE-2021-47584

Plugin Details

Severity: Medium

ID: 269071

File Name: unity_linux_UTSA-2025-987239.nasl

Version: 1.2

Type: local

Published: 10/7/2025

Updated: 10/15/2025

Supported Sensors: Nessus

Risk Information

VPR

Risk Factor: Medium

Score: 4.4

CVSS v2

Risk Factor: Medium

Base Score: 4.6

Temporal Score: 3.4

Vector: CVSS2#AV:L/AC:L/Au:S/C:N/I:N/A:C

CVSS Score Source: CVE-2021-47584

CVSS v3

Risk Factor: Medium

Base Score: 5.5

Temporal Score: 4.8

Vector: CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Temporal Vector: CVSS:3.0/E:U/RL:O/RC:C

Vulnerability Information

Required KB Items: Host/local_checks_enabled, Host/cpu, Host/UOS-Server/release, Host/UOS-Server/rpm-list

Exploit Ease: No known exploits are available

Patch Publication Date: 9/23/2025

Vulnerability Publication Date: 1/28/2022

Reference Information

CVE: CVE-2021-47584