Securelevels and /dev/io documentation inconsistency

[Giorgos Keramidas]

On 2006-07-12 15:47, Alexandros Kosiaris <akosiaris at gmail.com> wrote:
> Hello,
>
> I believe i have stumbled upon a documentation inconsistency
> concerning securelevels and usage of /dev/io
>
> >From init(8) manpage
>
>  1     Secure mode - the system immutable and system append-only flags may
>           not be turned off; disks for mounted file systems, /dev/mem,
>           /dev/kmem and /dev/io (if your platform has it) may not be opened
>           for writing; kernel modules (see kld(4)) may not be loaded or
>           unloaded.
>
> Note the "may not be opened for writing". It is correct for /dev/mem
> and /dev/kmem but incorrect for /dev/io as the following experiment
> shows:
>
> 3:40pm  ~ # sysctl kern.securelevel
> kern.securelevel: 1
> root at mybox
> 3:40pm  ~ # head /dev/io
> head: /dev/io: Operation not permitted
> root at mybox
> 3:40pm  ~ #
>
> Now the source code in /usr/src/sys/i386/i386/io.c just checks if
> securelevel is greater that 0 when opening the device and return
> accordingly.
>
> However from io(4)
>
> Note that even read-only access will grant the full I/O privileges.
>
> Which means that changing the code to check if the device is opened
> O_RDONLY and then allowing access would be a mistake cancelling the
> idea of blocking access to the device through usage of the
> securelevel.
>
> I am correct about the above ?
> Does the documentation need a correction in that place?

It looks like it does.  Would something like this be satisfactory?

    1		Secure mode - the system immutable and system
		append-only flags may not be turned off; disks for
		mounted file systems, /dev/mem and /dev/kmem may not be
		opened for writing and /dev/io (if your platform has it)
		may not be opened at all; kernel modules (see kld(4))
		may not be loaded or unloaded.

Regards,
Giorgos