Re: [PATCH v3 0/3] Actually fix freelist pointer vs redzoning

[Vlastimil Babka]

On 10/15/20 10:23 AM, Christopher Lameter wrote:
> On Wed, 14 Oct 2020, Kees Cook wrote:
>
> > Note on patch 2: Christopher NAKed it, but I actually think this is a
> > reasonable thing to add -- the "too small" check is only made when built
> > with CONFIG_DEBUG_VM, so it *is* actually possible for someone to trip
> > over this directly, even if it would never make it into a released
> > kernel. I see no reason to just leave this foot-gun in place, though, so
> > we might as well just fix it too. (Which seems to be what Longman was
> > similarly supporting, IIUC.)
>
> Well then remove the duplication of checks. The NAK was there because it
> seems that you were not aware of the existing checks.
>
> > Anyway, if patch 2 stays NAKed, that's fine. It's entirely separable,
> > and the other 2 can land. :)
>
> Just deal with the old checks too and it will be fine.

Yeah, the existing check is under CONFIG_DEBUG_VM, which means it's not active 
on some configurations. Creating a cache is not exactly fast path operation, so 
I would remove this guard.
As for the minimum size check, I would probably remove it (but watch out if 
SLAB/SLOB can handle it). It's not effective to use slab cache for 4-byte 
objects, but why make it an error.