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CVE-2021-46968: s390/zcrypt: fix zcard and zqueue hot-unplug memleak

• Severity: medium (CVSS 5.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2024-02-27 · updated 2026-06-17
• Weakness: CWE-401

Description

In the Linux kernel, the following vulnerability has been resolved: s390/zcrypt: fix zcard and zqueue hot-unplug memleak Tests with kvm and a kmemdebug kernel showed, that on hot unplug the zcard and zqueue structs for the unplugged card or queue are not properly freed because of a mismatch with get/put for the embedded kref counter. This fix now adjusts the handling of the kref counters. With init the kref counter starts with 1. This initial value needs to drop to zero with the unregister of the card or queue to trigger the release and free the object.

Affected products

• Linux kernel: from 5.10 before 5.10.36; from 5.11 before 5.11.20; from 5.12 before 5.12.3 — fixed in 5.10.36, 5.11.20, 5.12.3

How to fix

Upgrade to a fixed version: Linux kernel 5.10.36, 5.11.20, 5.12.3. Check the vendor advisory for mitigations.

References

• https://git.kernel.org/stable/c/026499a9c2e002e621ad568d1378324ae97e5524
• https://git.kernel.org/stable/c/055a063a18bcd19b93709e3eac8078d6b2f04599
• https://git.kernel.org/stable/c/70fac8088cfad9f3b379c9082832b4d7532c16c2
• https://git.kernel.org/stable/c/971dc8706cee47393d393905d294ea47e39503d3
• https://git.kernel.org/stable/c/026499a9c2e002e621ad568d1378324ae97e5524
• https://git.kernel.org/stable/c/055a063a18bcd19b93709e3eac8078d6b2f04599
• https://git.kernel.org/stable/c/70fac8088cfad9f3b379c9082832b4d7532c16c2
• https://git.kernel.org/stable/c/971dc8706cee47393d393905d294ea47e39503d3

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