I'm trying to implement a security module, using partly the root plug module, where I want to read-write a password in a USB flash key and take the appropriate decisions if the pass is right or not.
I've read that reading files from a disk in kernel mode is not a good thing to do.
So which is the right and secure way to do that? Can I just use bash scripting to read from usb and somehow pass the data to the kernel module? Maybe what I said is bull%@*t, I'm just trying to make a plan of how to work around this.. I suppose it's not secure to have the cryptography algorithm in plain text inside a script..
I just don't know where to focus my work because I don't really have a global perception about how exactly the kernel works.
Do you have any suggestions?
Thank you

At what point do you need the USB device? I use one with my system, but I hold off until right before login to use it (I need it for /home and a few non-standard mounts, but not the basic ones.) If you don't need it before /etc and fstab are processed, I'd suggest waiting until the last minute. If you can wait until / is mounted, either compile your kernel with USB support, or load the usb-storage module early on (rc.modules in Slackware.) If you can't wait until / is mounted, you (almost) definitely need to use an initrd, which is a pain in the ass. I've never had the patience to figure out setting one of those up.

BTW Yes, scripts work very well for this purpose. The exception is if you've encrypted the USB device and/or it cannot otherwise be found using findfs. You can explicitly specify the device name to mount, however all peripheral devices must be connected exactly the same (with the same kernel) every boot for that to work reliably. Also, on one of my systems the PCMCIA controller seems to get in the way so I have to wait until hotplug is done before I plug it in.
ta0kira

Thanks for the advice, I searched more on the subject and I think I can use more bash scripting than kernel programming to do what I want.