Merge branch '2022-04-29-fuzzing-and-asan-fixes'

To quote the author:

I've been experimenting with ASAN on sandbox and turned up a few issues
that are fixed in this series.

Basic ASAN was easy to turn on, but integrating with dlmalloc was
messier and fairly intrusive. Even when I had it working, there was only
a small redzone between allocations which limits the usefulness.

I saw another series on the list by Sean Anderson to enable valgrind
which was finding a different set of issues, though there was one
overlap that Sean is fixing with
"[PATCH] IOMUX: Fix access past end of console_devices".

With these issues fixed, I was able to run the dm tests without any ASAN
issues. There are a couple of leaks reported at the end, but that's for
another day.