Date: Wed, 12 Jul 2006 17:11:53 +0300 From: Giorgos Keramidas <keramida@freebsd.org> To: Alexandros Kosiaris <akosiaris@gmail.com> Cc: freebsd-current@freebsd.org, freebsd-stable@freebsd.org Subject: Re: Securelevels and /dev/io documentation inconsistency Message-ID: <20060712141153.GB30855@gothmog.pc> In-Reply-To: <cee728a70607120547q51b3e45flfe22716fd28b8c83@mail.gmail.com> References: <cee728a70607120547q51b3e45flfe22716fd28b8c83@mail.gmail.com>
next in thread | previous in thread | raw e-mail | index | archive | help
On 2006-07-12 15:47, Alexandros Kosiaris <akosiaris@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@mybox
> 3:40pm ~ # head /dev/io
> head: /dev/io: Operation not permitted
> root@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
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20060712141153.GB30855>