CVE-2020-29569

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.