[PATCH] Add file permission mode helpers

[Greg Kroah-Hartman]

On Wed, Aug 03, 2016 at 10:11:40AM +0200, Ingo Molnar wrote:
> An added advantage would be that during review it would stick out like a sore 
> thumb if anyone used a 'weird' permission variant.
> 
> For example, if you saw these lines in a driver patch:
> 
> +	__ATTR(l1, 0444, driver_show_l4, NULL);
> +		__ATTR(l3, 0446, driver_show_l4, NULL);
> +			__ATTR(l2, 04444, driver_show_l4, NULL);
> +		__ATTR(l4, 0444, driver_show_l4, NULL);
> 
> ... would you notice it at a glance that it contains two security holes?

I've tried to deal with that in the past with the __ATTR_RW() and
__ATTR_RO() and __ATTR_WO() macros that more should be using.  I swept
the tree a few years ago to try to fix up most of them, but I know I
didn't catch them all, and more files have been added since then.

> While the weird permissions in this:
> 
> +		__ATTR(l1, PERM_r__r__r__,  driver_show_l4, NULL);
> +		__ATTR(l3, PERM_r__r__rw_,  driver_show_l4, NULL);
> +		__ATTR(l2, PERM_sr__r__r__, driver_show_l4, NULL);
> +		__ATTR(l4, PERM_r__r__r__,  driver_show_l4, NULL);
> 
> Wouln't even build, because the dangerous patterns of PERM_r__r__rw_ or 
> PERM_sr__r__r__ are not defined to begin with.

Because of that, odds are people will just stick to the octal numbers,
because they think they want something other than the ones you defined
for foolish reasons :)

That being said, I do like them much better than the macros we have
today, which I always have to go and look up every time I see them...

thanks,

greg k-h