Re: [PATCH resend] mmc: Added ioctl to let userspace apps send ACMDs

[Arnd Bergmann <arnd@arndb.de>]

On Wednesday 23 March 2011, John Calixto wrote:
> 
> On Wed, 23 Mar 2011, Michał Mirosław wrote:
> > When you grant write access to a device to some user, you should
> > expect that it is all you are granting. There shouldn't be any hidden
> > doors that, for example, if underlying device is SD card then you can
> > destroy it by this ioctl(). Not counting wearing or WORM-like media,
> > writes (also erasing, changing encryption keys, etc.) are undoable.
> > Other forms of access should be granted separately (by capabilities or
> > other means).
> > 
> 
> Fair enough.  I'm not aware enough of the other ACMDs that might
> actually destroy the card (nothing I'm using will destroy the card), so
> I'll be sure to hook it with CAP_SYS_ADMIN (or whatever capability is
> most appropriate).

The standard defines some commands as vendor-specific. A typical use
case for these would be a way to update the firmware on the embedded
microcontroller of the card.

Overwriting that firmware with garbage would be an obvious way to
brick the card.

	Arnd