Re: [CentOS] mount toption: nodev

On Tue, 2009-09-15 at 15:21 -0400, Yungwei Chen wrote:

Hi,

            I am trying to secure my CentOS file systems by

introducing "nodev" to devies defined in /etc/fstab. I learned that "nodev" prevents users from mounting unauthorized devices. However, I can still mount a cdrom to /tmp/cdrom with the following defined in /etc/fstab. Am I missing something? Thanks.

            LABEL=/tmp              /tmp                    ext3

defaults,nodev 1 2

Yes, I think that you have misinterpreted the "nodev" option.

That means that "device" files ( normally created under /dev ) in a filesystem mounted with the "nodev" option are not allowed to access the hardware that they represent. This is used primarily as a protection against malware that tries to get direct access to hardware such as memory or network cards by creating additional device files somewhere else.

Since CentOS ( and most other recent distros ) use "udev" to create the necessary block and character files in the /dev tree ( which is NOT an ext3 filesystem ) there should be no need for the "average" user to create device files anywhere else in the directory tree. After I understood this, I then modified all of the systems that I take care of to specify "nodev" as an option for ALL ext3 filesystems.

In your case, if you are mounting a CD, you are using the normal block device(s) in /dev ( such as /dev/cdrom or /dev/hdc ) and just specifying the directory to use as the mount point ( /tmp/cdrom ), which is perfectly legal with this option.