Hi Felix,
I actually have that guy's book who wrote that article
- The book of Xen - very good book indeed!
What I really wish to do, is provide a similar sort of
thing to that SSH setup, except allow it to be accessed via a web
browser. I have an idea where I can use ajaxterm and some PHP
scripting. Once a user logs on with a username and password, I could
tell php to start ajaxterm and piple xm console through it. This is
what Slicehost does I think. The console would be protected with php
sessions.
But my main worry was whether or not the Dom0 could be
compramised via the above method, but I don't think that's the case.
Thanks
Jonathan
Hi Jonathan,
this is a common way to reset lost / forgotton root passwords:
You need:
- Physical access to a machine (if you want to reset the password of
the Dom0 or a native linux) or console access to a DomU
- Access to the kernel command line, via lilo, grub or pygrub/pvgrub in
XEN
Then you do:
- Modify the kernel command line, add the init=/bin/bash option, for
example: kernel /linux-2.6.32.15-xen root=/dev/xvda2 init=/bin/bash
- You'll directly end up in a root console without password or any
services started after the kernel booted
- enter those commands:
mount -o remount,rw /
passwd root
<enter new password>
exec /sbin/init
The root password will then be the newly set one.
DomUs generally are not vulnerable to this method, as long as the
kernel command line is set in the domain configuration. But
pygrub/pvgrub is a nice thing for hosting customers, because they can
compile their own kernels, containing their preferred settings, modules
and builtin functionality. Generally this problem is avoided by adding
a password to grub, but some customers may forget that step.
So physical access can always be a strong weapon, but it is necessary
for repairing a machine or for some advanced setups (especially when
setting up a firewall, one easily gets locked out of the server...). I
think the best way is securing this access, by restricting virtual
console access to highly encrypted and authenticated sessions (IMHO the
best way is SSH here).
I'd also think about customers forgetting to log out, because leaving
xm console does *not* logout root inside the console.
The tutorial I posted to your I/O question contains a SSH-based setup
for xm console access with sudo, which may be nice to start with. I
personally use an own wrapper inside a chroot jail, to provide the
ability of entering commands like create / rescue / setup (rescue
starts another domain configuration with NFS root + rescue-Kernel,
setup starts a virtual Debian setup). It's quite handy for VPS
customers.
Regards,
Felix
Am 18.06.2010 14:26, schrieb Jonathan Tripathy:
Hi Felix,
Thanks for the email.
>a simple init=/bin/bash added to the kernel
command line allows resetting the root password...
ok this worries me. Can you please explain this a little further? Do
you need to have access to the Dom0 to begin with?
Thanks
Hi Jonathan,
do you definitely need a web console (so really browser-based) or would
you consider a SSH-based console?
I personally prefer SSH because it is more secure, easier to set up and
it is somehow the default way of accessing remote consoles. You can do
a modified SSH setup that only allows access to the console, or
optionally, access to xm console, xm list, xm shutdown, xm create but
restricted to the own VM of your customer. With chroot-jails etc.,
other commands cannot be executed.
SSH also has the advantage of good copy & paste of larger commands,
and the possibility to work with multiple client certificates and / or
passwords. Probably your administrative interface allows uploading of
multiple public keys, so that your customers can have multiple
adminsitrative accounts for the server (but only one can access the
console at a time).
I've got no experiences with ajaxterm, but you should really control
its security:
Console access is quite useful for hackers, e.g. some customer may
forget to log out root or if you use pvgrub / pygrub, a simple
init=/bin/bash added to the kernel command line allows resetting the
root password...
So it must be a really secure application, not vulnerable to XSS, SQL
Injections, Connection hijacking, ... and SSL encrypted.
Regards,
Felix Kuperjans
Am 18.06.2010 13:02, schrieb Jonathan Tripathy:
Hi Everyone,
Does anyone have any idea on how to give my
customers a "web console" for their VMs?
Using
http://antony.lesuisse.org/software/ajaxterm/ I
can manually set up a remote session for them, by doing
ajaxterm.py -c xm console <DOMNAME>
However is there any way to make this automatic? Maybe I could put it in the vif script?
Thanks
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