An issue was discovered in the Linux kernel through 5.10.1, as used with Xen through 4.14.x. The Linux kernel PV block backend expects the kernel thread handler to reset ring->xenblkd to NULL when stopped. However, the handler may not have time to run if the frontend quickly toggles between the states connect and disconnect. As a consequence, the block backend may re-use a pointer after it was freed. A misbehaving guest can trigger a dom0 crash by continuously connecting / disconnecting a block frontend. Privilege escalation and information leaks cannot be ruled out. This only affects systems with a Linux blkback.

References

• https://nvd.nist.gov/vuln/detail/CVE-2020-29569
• https://lists.debian.org/debian-lts-announce/2021/02/msg00018.html
• https://lists.debian.org/debian-lts-announce/2021/03/msg00010.html
• https://security.gentoo.org/glsa/202107-30
• https://security.netapp.com/advisory/ntap-20210205-0001/
• https://www.debian.org/security/2021/dsa-4843
• https://xenbits.xenproject.org/xsa/advisory-350.html