On Wednesday 16 November 2005 02:19, Miklos Szeredi wrote:
> > > This is why we have "pivot_root()" and "chroot()", which can both be
> > > used to do what you want to do. You mount the new root somewhere else,
> > > and then you chroot (or pivot-root) to it. And THEN you do 'chdir("/")'
> > > to move the cwd into the new root too (and only at that point have you
> > > "lost" the old root - although you can actually get it back if you have
> > > some file descriptor open to it).
> >
> > Wouldn't this constitute a security flaw?
> >
> > Shouldn't chroot jail you?
>
> No, chroot should just change the root.
>
> If you don't want to be able to get back the old root, just close all
> file descriptors _in addition_ to chroot() and chdir().
If you try the chdir by filedescriptor trick on the stdin/stdout/stderr fed
into PID 1 when it's started up by the kernel, which filesystem do you wind
up in? (rootfs?)
I ask because switch_root redoes those to point to /dev/console from the real
root (presumably for security reasons), and this happens _before_ the init on
the real root gets called, and thus before the real root gets to populate
its' own dynamic /dev.
I suppose initramfs could make a temporary /dev, do the mknods for console and
the real root, and then mount --move this tmpdir to the real root's /dev once
that's available (and then let the real root's udev populate it the rest of
the way). Or the real root could have a hard /dev/console living in the
directory that's going to get overmounted by tmpfs later. Or just leave
initramfs accessible until init can switch consoles...
Sigh. I need to document the requirements here...
Rob
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
