CentOS - Sep 2010 - why does automounting removable media always have options nodev, noexec, nosuid?

i'm experimenting with some basic removable media mounting
exercises for an upcoming class, and i read that, while you can use
gconf-editor to change some of the mount options in cases like that,
there is no way to override the mount options of nodev, noexec and
nosuid.  for example, that claim is made here (admittedly for fedora,
but it appears to be true for centos as well):

  http://scrolls.mafgani.net/2007/03/gnome-automount-options/

is there somewhere that one could see and verify that those options
always hold for mountable filesystems on removable media?  thanks.

rday

-- 

=======================================================================Robert P.
J. Day                               Waterloo, Ontario, CANADA

        Top-notch, inexpensive online Linux/OSS/kernel courses
                        http://crashcourse.ca

Twitter:                                       http://twitter.com/rpjday
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========================================================================

On Wed, Sep 15, 2010 at 03:09:39PM -0400, Robert P. J. Day
wrote:
>   i'm experimenting with some basic removable media mounting
> exercises for an upcoming class, and i read that, while you can use
> gconf-editor to change some of the mount options in cases like that,
> there is no way to override the mount options of nodev, noexec and
> nosuid.  for example, that claim is made here (admittedly for fedora,
> but it appears to be true for centos as well):
> 
>   http://scrolls.mafgani.net/2007/03/gnome-automount-options/
> 
> is there somewhere that one could see and verify that those options
> always hold for mountable filesystems on removable media?  thanks.
I'm sure you could look in the source for verification.

But as for *why*: if you could mount removable media with suid executables
or device files, in order to get root access on a system, all you'd need to
do is make a filesystem containing a setuid root shell. Or a world rw
/dev/sda.

-- 
Matthew Miller           mattdm at mattdm.org         
<http://mattdm.org/>

On Wed, Sep 15, 2010 at 9:09 AM, Robert P. J. Day <rpjday at
crashcourse.ca>wrote:
>
>  i'm experimenting with some basic removable media mounting
> exercises for an upcoming class, and i read that, while you can use
> gconf-editor to change some of the mount options in cases like that,
> there is no way to override the mount options of nodev, noexec and
> nosuid.  for example, that claim is made here (admittedly for fedora,
> but it appears to be true for centos as well):
>
>  http://scrolls.mafgani.net/2007/03/gnome-automount-options/
>
> is there somewhere that one could see and verify that those options
> always hold for mountable filesystems on removable media?  thanks.
>
This question is different from the one in your subject header. These mount
options are 'security features', make crackers jump through another
hoop.
They can be undone with a mount -o remount. I don't know the answer to your
second question about where the defaults are set/displayed.
TDB
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On Wed, Sep 15, 2010 at 10:26:12AM -1000, Dave wrote:
> This question is different from the one in your subject header. These
> mount options are 'security features', make crackers jump through
another
> hoop. They can be undone with a mount -o remount.
If one can jump through that hoop, one already has root and doesn't need to.

-- 
Matthew Miller           mattdm at mattdm.org         
<http://mattdm.org/>