Spoiler alert, you almost certainly have been completely pwned already if someone can set LD_PRELOAD or modify /etc/ld.so.conf.
One such assumption is "if /bin/foo is a trustworthy executable then any process with /proc/pid/exe pointing to /bin/foo is trustworthy"
We know that this isn't anything revolutionary, but most people assume that this kind of thing can't happen, so we wrote a blog post about it.
What's the relevance of symlinks here?
That said, your example doesn't make much sense to me. I'd be willing to bet a lot of money that the authors of the exploit chain you mentioned are aware of LD_PRELOAD and /etc/ld.so.conf.