svn commit: r354458 - head/libexec/rc/rc.d

[Conrad Meyer]

Hi,

Response inline below.

On Sun, Nov 10, 2019 at 08:08 Edward Tomasz Napierala <trasz at freebsd.org>
wrote:

> On 1109T2049, Alexander Leidinger wrote:
> > Quoting Edward Tomasz Napierala <trasz at freebsd.org> (from Thu, 7 Nov
> > 2019 18:15:24 +0000 (UTC)):
> >
> > > Author: trasz
> > > Date: Thu Nov  7 18:15:24 2019
> > > New Revision: 354458
> > > URL: https://svnweb.freebsd.org/changeset/base/354458
> > >
> > > Log:
> > >   Extend the linux rc script to mount the neccessary file systems,
> > >   set ELF fallback brand, and load pty(4).
> >
> > We never did something like that. We have it documented everywhere
> > that it needs to be done manually. So this is at least a POLA
> > violation. It is great that the nocover option is used in the mount,
> > but it's still some kind of layering violation (I may want to have
> > only a subset mounted, or nothing at all).
>
> It is kind of a POLA violation, but previously the linux_enable
> knob didn't do much apart from loading the linux{,64}.ko kernel
> module and doing something weird with ldconfig, which I'm not
> even sure is actually useful.  In other words, the old behaviour
> can be restored by just not using linux_enable, and instead
> loading the kernel modules the same way all the others are loaded.
>
> Could you give me some use case why someone would want only a subset
> of the filesystems?


They’re an additional attack surface.  If your few linux applications get
by with fewer vfs, you might want to avoid the others. I’m not particularly
attached to this reason. And imo, linux64.ko kind of dwarf that attack
surface concern, so it’s maybe a silly point.

Another problem with the current code is (and I may be mistaken here) I
think that it ignores mount options configured in the admin’s /etc/fstab.
Eg I configure my /tmp with a hard limit on memory use and if I were to
mount a compat shm tmpfs, I’d also want its memory use bounded. “Nocover”
protects from covering any existing “auto“ mounts, but one can imagine
specifying the linux compat mount “noauto”.

I am on board with making this stuff more “batteries included” and usable
by default, but just echoing the request for configurable knobs (I don’t
care about the defaults).

Best,
Conrad

>
>
> > I do not object to the functionality, but I think it needs to be
> > configurable (an option to influence if the auto-mount is done or not,
> > doesn't matter to me what the default behavior is, as long as it is
> > configurable) and documented (UPDATING, handbook, man-pages, maybe
> > even the release notes).
>
> Man page updates are pending review at https://reviews.freebsd.org/D22277.
> Good point about the Handbook and release notes; I'll take a look.
>
>