Re: [PATCH] mm/mincore: allow for making sys_mincore() privileged

Linus Torvalds wrote on Wed, Jan 16, 2019:

*Very* few people want to run their databases as root.

In the case of happycache, this isn't the database doing the
dump/restore, but a separate process that could have the cap - it's
better if we can do without though, and from his readme he runs as user
cassandra in the /var/lib/cassandra directory for example so that'd
match the file owner.

For pgfincore, it's a postgres extension so the main process does it -
but it does have files open as write as well as being the owner.

Jiri's original patch kind of acknowledged that by making the new test
be conditional, and off by default. So then it's a "only do this for
lockdown mode, because normal people won't find it acceptable".

And I'm not a huge fan of that approach. If you don't protect normal
people, then what's the point, really?

I agree with that. 
"Being owner or has cap" (whichever cap) is probably OK.
On the other hand, writeability check makes more sense in general -
could we somehow check if the user has write access to the file instead
of checking if it currently is opened read-write?

-- 
Dominique