In the Linux kernel 5.4.0-rc2, there is a use-after-free (read) in the
__blk_add_trace function in kernel/trace/blktrace.c (which is used to fill
out a blk_io_trace structure and place it in a per-cpu sub-buffer).

Tristan Madani discovered that the block I/O tracing implementation in the
Linux kernel contained a race condition. A local attacker could use this to
cause a denial of service (system crash) or possibly expose sensitive
information.