runtime: ensure the fixalloc object size is valid
Usually, fixalloc is used to allocate small, persistent and reuseable
objects. The size is typically between range [sizeof(mlink), _FixAllocChunk].
It's rare for being out of the range. But if it did happen, we got a
hard-to-discover memory corruption. This commit prevents that situation by limiting object's size.
Change-Id: If6ef8b0831596464e0f55d09f79094b79ae08c66
GitHub-Last-Rev:
cb8b1b01bbf452195f4f098d53cca74affc496ff
GitHub-Pull-Request: golang/go#47395
Reviewed-on: https://go-review.googlesource.com/c/go/+/337429
Reviewed-by: Austin Clements <austin@google.com>
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Cherry Mui <cherryyz@google.com>