Divide By Zero Affecting kernel-macros package, versions <5.14.21-150500.55.73.1
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-SLES155-KERNELMACROS-7695851
- published17 Aug 2024
- disclosed16 Aug 2024
Introduced: 16 Aug 2024
CVE-2021-47584 (opens in a new tab)How to fix?
Upgrade SLES:15.5 kernel-macros to version 5.14.21-150500.55.73.1 or higher.
NVD Description
Note: Versions mentioned in the description apply only to the upstream kernel-macros package and not the kernel-macros 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