The Project Zero blog has posted a
detailed look at CVE-2021-0920 in the first of a two-part series on how
this bug created a vulnerability that was subsequently exploited.

Google’s Threat Analysis Group (TAG) discovered Samsung browser
exploit chains being used in the wild. TAG then performed root
cause analysis and discovered that this vulnerability,
CVE-2021-0920, was being used to escape the sandbox and elevate
privileges. CVE-2021-0920 was reported to Linux/Android
anonymously. The Google Android Security Team performed the full
deep-dive analysis of the exploit.

This issue was initially discovered in 2016 by a RedHat kernel
developer and disclosed in a public email thread, but the Linux
kernel community did
not patch the issue until it was re-reported
in 2021.

Source: LWN.net – The quantum state of Linux kernel garbage collection (Project Zero)