On Sun, Jul 03, 2011 at 11:27 -0700, Linus Torvalds wrote:
> That patch is entirely insane. No way in hell will that ever get merged.
Sure, this is just an RFC :) I didn't think about proposing it as a
patch as is, I tried to just show how/what checks it introduces.
> copy_to/from_user() is some of the most performance-critical code, and
> runs a *lot*, often for fairly small structures (ie 'fstat()' etc).
>
> Adding random ad-hoc tests to it is entirely inappropriate. Doing so
> unconditionally is insane.
That's why I've asked whether it makes sense to guard it with
CONFIG_XXX, defaults to =n. Some distributions might think it makes
sense to enable it sacrificing some speed.
Will do.
> If you seriously clean it up (that at a minimum includes things like
> making it configurable using some pretty helper function that just
> compiles away for all the normal cases,
Hm, it is not as simple as it looks at the first glance - even if the
object size is known at the compile time (__compiletime_object_size), it
might be a field of a structure, which crosses the slab object
boundaries because of an overflow.
However, if interpret constants fed to copy_*_user() as equivalent to
{get,put}_user() (== worry about size argument overflow only), then it
might be useful here.
> if (!slab_access_ok(to, n) || !stack_access_ok(to, n))
OK :)
Thanks!
--
Vasiliy Kulikov
http://www.openwall.com - bringing security into open computing environments
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