CVE-2021-47533: linux kernel Use-After-Free — Fix

Description

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.

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CVSS v3.1 Score

7.8

HIGH

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Weakness Type (CWE)

CWE-416 Use After Free

Affected Products

Vendor	Product	Versions
linux	linux_kernel	5.12 — 5.15.7
linux	linux_kernel	All
linux	linux_kernel	All
linux	linux_kernel	All

References

Advisories & Patches

https://git.kernel.org/stable/c/2931db9a5ed219546cf2ae0546698faf78281b89 https://git.kernel.org/stable/c/d134c5ff71c7f2320fc7997f2fbbdedf0c76889a https://git.kernel.org/stable/c/2931db9a5ed219546cf2ae0546698faf78281b89 https://git.kernel.org/stable/c/d134c5ff71c7f2320fc7997f2fbbdedf0c76889a

Frequently Asked Questions

What is CVE-2021-47533? +

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. It has a CVSS v3.1 base score of 7.8 (HIGH).

How severe is CVE-2021-47533? +

CVE-2021-47533 has a CVSS v3.1 score of 7.8 out of 10, rated HIGH. This is a high-severity vulnerability that should be prioritized for patching.

What products are affected by CVE-2021-47533? +

CVE-2021-47533 affects products from linux, specifically: linux_kernel. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2021-47533? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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