Re: [PATCH v2 1/3] x86/mce: Avoid infinite loop for copy from user recovery

Al Viro
2021-08-21T21:51:47Z

On Fri, Aug 20, 2021 at 09:51:41PM -0700, Tony Luck wrote:
> On Fri, Aug 20, 2021 at 1:25 PM Luck, Tony <tony.luck@intel.com> wrote:
> > Probably the same for the two different addresses case ... though I'm
> > not 100% confident about that. There could be some ioctl() that peeks
> > at two parts of a passed in structure, and the user might pass in a
> > structure that spans across a page boundary with both pages poisoned.
> > But that would only hit if the driver code ignored the failure of the
> > first get_user() and blindly tried the second. So I'd count that as a
> > critically bad driver bug.
>
> Or maybe driver writers are just evil :-(
>
> for (i = 0; i < len; i++) {
> tx_wait(10);
> get_user(dsp56k_host_interface.data.b[1], bin++);
> get_user(dsp56k_host_interface.data.b[2], bin++);
> get_user(dsp56k_host_interface.data.b[3], bin++);
> }

Almost any unchecked get_user()/put_user() is a bug. Fortunately, there's
not a lot of them
<greps>
93 for put_user() and 73 for get_user(). _Some_ of the former variety might
be legitimate, but most should be taken out and shot.

And dsp56k should be taken out and shot, period ;-/ This is far from the
worst in there...