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    SubjectRE: [linux-fbdev] fbdev 2.4.0 cleanups
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    Surely you let anyone open a /dev/fb* but then deny anyone but that user
    RE-opening it? This is a well-documented way of securing devices.


    Nicholas Vinen

    -----Original Message-----
    From: owner-linux-kernel@vger.rutgers.edu
    [mailto:owner-linux-kernel@vger.rutgers.edu]On Behalf Of Russell King
    Sent: Wednesday, March 15, 2000 11:53 AM
    To: James A Simmons
    Cc: Sven LUTHER; Petr Vandrovec; Geert Uytterhoeven; FrameBuffer List;
    Linux Kernel Mailing List
    Subject: Re: [linux-fbdev] fbdev 2.4.0 cleanups


    James A Simmons writes:
    > > But anyway, i don't agree with you, there is no reason that a lots of
    people
    > > can open /dev/fb in read only mode, sure if some guys want to write to
    it at
    > > the same time, it could cause problems, ...
    >
    > Security :) One of the goals is to allow anyone to run a app on /dev/fb.
    > No more root.

    Erm, this is probably a silly question, especially as I haven't been
    following
    this thread in depth.

    If you're concerned about security, then you don't really want anyone to be
    able to open /dev/fb and read what you've got on your console. Think about
    it - allowing anyone to open /dev/fb means that you might as well broadcast
    the picture that is on your monitor to everyone who has access to your
    machine.

    I think think what you really want is to allow the user logged into the
    console to be able to read/write the framebuffer, in much the same way that
    /dev/console, /dev/dsp and friends are handled in a RedHat system - the
    ownership of these "console" based devices is changed when a user logs in
    at the console.

    Alternatively, the only other solution is to keep /dev/fb as "root only" and
    have a suid program (tsk tsk) which drops it's privs directly after opening
    /dev/fb. This allows "root" to control who can access /dev/fb.

    Both of the above methods have their drawbacks in that neither of them can
    be 100% secure when you may have multiple users logging in on the VCs, but
    then that in itself is inherently insecure way of operating. ;)
    _____
    |_____| ------------------------------------------------- ---+---+-
    | | Russell King rmk@arm.linux.org.uk --- ---
    | | | | http://www.arm.linux.org.uk/~rmk/aboutme.html / / |
    | +-+-+ --- -+-
    / | THE developer of ARM Linux |+| /|\
    / | | | --- |
    +-+-+ ------------------------------------------------- /\\\ |

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