Linux Kernel up to 6.16.8 zram zram_slot_lock race condition

Summaryinfo

A vulnerability was found in Linux Kernel up to 6.16.8. It has been classified as critical. Affected by this issue is the function zram_slot_lock of the component zram. This manipulation causes race condition. This vulnerability is handled as CVE-2025-39941. There is not any exploit available. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability was found in Linux Kernel up to 6.16.8. It has been declared as critical. Affected by this vulnerability is the function zram_slot_lock of the component zram. The manipulation with an unknown input leads to a race condition vulnerability. The CWE definition for the vulnerability is CWE-362. The product contains a code sequence that can run concurrently with other code, and the code sequence requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence that is operating concurrently. The impact remains unknown. The summary by CVE is:

In the Linux kernel, the following vulnerability has been resolved: zram: fix slot write race condition Parallel concurrent writes to the same zram index result in leaked zsmalloc handles. Schematically we can have something like this: CPU0 CPU1 zram_slot_lock() zs_free(handle) zram_slot_lock() zram_slot_lock() zs_free(handle) zram_slot_lock() compress compress handle = zs_malloc() handle = zs_malloc() zram_slot_lock zram_set_handle(handle) zram_slot_lock zram_slot_lock zram_set_handle(handle) zram_slot_lock Either CPU0 or CPU1 zsmalloc handle will leak because zs_free() is done too early. In fact, we need to reset zram entry right before we set its new handle, all under the same slot lock scope.

It is possible to read the advisory at git.kernel.org. This vulnerability is known as CVE-2025-39941 since 04/16/2025. The exploitation appears to be difficult. Technical details of the vulnerability are known, but there is no available exploit.

Upgrading to version 6.16.9 eliminates this vulnerability. Applying the patch ff750e9f2c4d63854c33967d1646b5e89a9a19a2/ce4be9e4307c5a60701ff6e0cafa74caffdc54ce is able to eliminate this problem. The bugfix is ready for download at git.kernel.org. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the vulnerability database at CERT Bund (WID-SEC-2025-2194). Be aware that VulDB is the high quality source for vulnerability data.

Affected

• Google Container-Optimized OS
• Debian Linux
• Google Cloud Platform
• Amazon Linux 2
• Red Hat Enterprise Linux
• Ubuntu Linux
• SUSE Linux
• Oracle Linux
• SUSE openSUSE
• Open Source Linux Kernel
• RESF Rocky Linux
• NetApp ActiveIQ Unified Manager
• IBM QRadar SIEM
• Dell NetWorker

Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 6.16.0
• 6.16.1
• 6.16.2
• 6.16.3
• 6.16.4
• 6.16.5
• 6.16.6
• 6.16.7
• 6.16.8

License

• open-source

Website

• Vendor: https://www.kernel.org/

CPE 2.3info

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CPE 2.2info

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Entryinfo

Be aware that VulDB is the high quality source for vulnerability data.

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