Re: Security fix for remapping of page 0 (was [PATCH] Change ZERO_SIZE_PTR to point at unmapped space)

Linus Torvalds
2009-06-03T19:27:52Z

On Wed, 3 Jun 2009, Christoph Lameter wrote:
>
> We could just move the check for mmap_min_addr out from
> CONFIG_SECURITY?

No.

The thing is, the security model wants to modify the rules on what's
"secure" and what isn't. And your patch just hard-coded that
capable(CAP_SYS_RAWIO) decision - but that's not what something like
SElinux actually uses to decide whether it's ok or not.

So if you do it in generic code, you'd have to make it much more complex.
One option would be to change the rule for what "security_file_mmap()"
means, and make the return value says "yes, no, override". Where
"override" would be "allow it for this process even if it's below the
minimum mmap limit.

But the better option really is to just copy the cap_file_mmap() rule to
the !SECURITY rule, and make !SECURITY really mean the same as "always do
default security", the way it's documented.

Linus