In the quest to remove all stack VLA usage from the kernel[1], this
switches to using a kasprintf()ed buffer. Return paths are updated
to free the allocation.

[1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.comSigned-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>