Re: dynamic /dev security hole?

Marc Ballarin
2004-08-08T15:56:40Z

On 08 Aug 2004 08:47:40 -0400
Albert Cahalan <albert@users.sf.net> wrote:

> Suppose I have access to a device, for whatever legit
> reason. Maybe I'm given access to a USB key with
> some particular serial number.
>
> I hard link this to somewhere else. Never mind that an
> admin could in theory use 42 separate partitions and
> mount most of the system with the "nodev" option. This
> is rarely done.
>
> Now the device is removed. The /dev entry goes away.
> A new device is added, and it gets the same device
> number as the device I had legit access to. Hmmm?

This would require (1) /dev to be inside the root filesystem and (2) users
having write access somewhere in that filesystem.

(1) is uncommon, often a separate filesystem is used for udev
(2) is very bad practice anyway and should never be seen on a true
multi-user machine

Besides, this is nothing new. Dynamic permission updates through PAM have
the same issue, and anyone calling themselves "admin" should be well aware
of those issues. This is basic Unix-security, after all.

Yet, this issue should probably mentioned in documentation. It certainly
should be mentioned in the udev-HOWTO.

Regards