Divide By Zero Affecting kernel-azure package, versions <5.14.21-150500.33.60.1
Threat Intelligence
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Test your applications- Snyk IDSNYK-SLES155-KERNELAZURE-7434962
- published10 Jul 2024
- disclosed9 Jul 2024
Introduced: 9 Jul 2024
CVE-2021-47584 (opens in a new tab)How to fix?
Upgrade SLES:15.5 kernel-azure to version 5.14.21-150500.33.60.1 or higher.
NVD Description
Note: Versions mentioned in the description apply only to the upstream kernel-azure package and not the kernel-azure package as distributed by SLES.
See How to fix? for SLES:15.5 relevant fixed versions and status.
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.
References
- https://www.suse.com/security/cve/CVE-2021-47584.html
- https://bugzilla.suse.com/1226564
- https://git.kernel.org/stable/c/3a1a4eb574178c21241a6200f4785572e661c472
- https://git.kernel.org/stable/c/a7c80674538f15f85d68138240aae440b8039519
- https://git.kernel.org/stable/c/edaa26334c117a584add6053f48d63a988d25a6e