On Wed, Jul 18, 2012 at 4:02 PM, Rich Freeman <ri...@gentoo.org> wrote: > On Wed, Jul 18, 2012 at 3:40 PM, Michael Mol <mike...@gmail.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
