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 were done with the wait so that we dont carry over a pointer to a freed structure.

Weakness

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory “belongs” to the code that operates on the new pointer.

Affected Software

Potential Mitigations

References

• 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