Re: [gentoo-dev] Opinion against /usr merge

[Michael Mol]

On Wed, Jul 18, 2012 at 4:02 PM, Rich Freeman <rich0@g.o> wrote:
> On Wed, Jul 18, 2012 at 3:40 PM, Michael Mol <mikemol@×××××.com> wrote:
>> So your initramfs doesn't include network tools such as ping,
>> traceroute or wget. Fine. Fundamentally speaking, why shouldn't
>> someone else's?
>
> So, an initramfs is just a piece of kernel functionality.  You can do
> almost ANYTHING in an initramfs, subject to the limitation that it is
> stored in RAM without any backing store.

Yup. IIRC, it has effectively the same underlying implementation as
tmpfs, using always-dirty file cache pages.

>
> There are lots of reasons to use an initramfs, and the biggest ones
> don't pertain much to Gentoo.  Here are some of the big use cases:
>
> 1.  One-size-fits-all kernel.  You want to support root and /usr on
> any filesystem, on any kind of hard drive, or on a SAN, or who knows
> where.  That either means saying Y to every driver in the kernel, or
> saying M and using an initramfs to load what is needed to get to root.
>
> 2.  One-size-fits-all grub config.  You put the smarts in the
> initramfs, and use filesystem labels and such to identify partitions.
>
> 3.  Use of labels/UUIDs on partitions.  When mdadm decides to renumber
> half your devices on a whim or you add a drive and everything bubbles
> down by one, your system still boots.
>
> 4.  Cleaner mounting of root, ability to fsck on initial mount, etc.
>
> 5.  When something goes wrong you can get a dash/bash shell instead of
> a grub shell.  The former is clearly more useful even if you don't
> have firefox+X11 in your initramfs.
>
> 6.  Support for booting off of stuff that the kernel can't find on its
> own, like SANs/etc.  That might require network support in the
> initramfs, and that usually isn't a big deal.  If somebody can spoof
> DNS on your fiber channel interface you've got bigger problems.
>
> Sure, the more you do with the initramfs the bigger the potential
> security risks.  Most distros don't have users build either kernels or
> initramfs which means they can just push updates, but that requires #1
> above, which I think most Gentoo users would not appreciate.

I fall into use cases 3 and 5, myself. Incidentally, bash is also
network-aware. (Not sure if the default USE flag set allows it,
though.) Were I to explicitly add network-aware tools, I'd probably
add either ssh/sftp/scp or links.

>
> However, the initramfs shouldn't leave much of anything running after
> it chroots, so the window should be fairly small.

So is the window for spoofing DNS responses. That didn't stop DNS
hijacking from being fairly easy. (And why there was a large
coordinated, cross-vendor effort to add source-port randomization once
it was shown to be easy.)

Multi-threaded native code has been my day job for the last five
years. I may be a bit biased when it comes to race conditions.

-- 
:wq