Most consumers of g_metadata_store were passing in partially unallocated
memory, resulting in stack garbage being written to disk labels. Fix them by
zeroing the memory first.
gvirstor repeated the same mistake, but in the kernel.
Also, glabel's label contained a fixed-size string that wasn't
initialized to zero.
PR: 222077
Reported by: Maxim Khitrov <max@mxcrypt.com>
Reviewed by: cem
MFC after: 3 weeks
X-MFC-With: 323314
X-MFC-With: 323338
Differential Revision: https://reviews.freebsd.org/D14164
f5b4099e6b