Linux Kernel up to 5.15.6 drm_crtc_commit_put use after free

Summaryinfo

A vulnerability described as critical has been identified in Linux Kernel up to 5.15.6. This affects the function drm_crtc_commit_put. Such manipulation leads to use after free. This vulnerability is referenced as CVE-2021-47533. No exploit is available. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability was found in Linux Kernel up to 5.15.6 and classified as critical. Affected by this issue is the function drm_crtc_commit_put. The manipulation with an unknown input leads to a use after free vulnerability. Using CWE to declare the problem leads to CWE-416. Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code. Impacted is confidentiality, integrity, and availability. CVE summarizes:

In the Linux kernel, the following vulnerability has been resolved: drm/vc4: kms: Clear the HVS FIFO commit pointer once done Commit 9ec03d7f1ed3 ("drm/vc4: kms: Wait on previous FIFO users before a commit") introduced a wait on the previous commit done on a given HVS FIFO. However, we never cleared that pointer once done. Since drm_crtc_commit_put can free the drm_crtc_commit structure directly if we were the last user, this means that it can lead to a use-after free if we were to duplicate the state, and that stale pointer would even be copied to the new state. Set the pointer to NULL once we're done with the wait so that we don't carry over a pointer to a free'd structure.

The advisory is shared for download at git.kernel.org. This vulnerability is handled as CVE-2021-47533 since 05/24/2024. There are known technical details, but no exploit is available. The current price for an exploit might be approx. USD $0-$5k (estimation calculated on 09/19/2025).

Upgrading to version 5.15.7 eliminates this vulnerability. Applying the patch 2931db9a5ed2/d134c5ff71c7 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.

Once again VulDB remains the best source for vulnerability data.

Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 5.15.0
• 5.15.1
• 5.15.2
• 5.15.3
• 5.15.4
• 5.15.5
• 5.15.6

License

• open-source

Website

• Vendor: https://www.kernel.org/

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