Re: [PATCH nf] netfilter: nft_set_rbtree: narrow down range completion to anonymous sets

[Pablo Neira Ayuso <pablo@netfilter.org>]

On Thu, Oct 08, 2026 at 12:52:35PM +0200, Pablo Neira Ayuso wrote:
> On Thu, Oct 08, 2026 at 08:32:54AM +0200, Florian Westphal wrote:
> > Pablo Neira Ayuso <pablo@netfilter.org> wrote:
> > > For anonymous sets, when adjacent ranges are found, the end element is
> > > not added to the set to pack the set representation. Use next start
> > > element to complete this interval.
> > > 
> > > Jérémy Jean says:
> > > 
> > > Consider two ranges in a netfilter verdict map:
> > > * keys 10-19 accept packets, and
> > > * keys 30-39 jump to chain 'victim'.
> > > Now, delete the end marker at 20. The lookup array now uses element 30
> > > as the first range's end, so an INTERVAL_END query for key 15 returns
> > > element 30, including its jump verdict and chain pointer. This can make
> > > KASAN reports a UAF after the GC releases reference chain for 30 that
> > > has expired:
> > 
> > Dumb question: How is it possible to remove an element if the map is
> > anonymous?
> 
> I suspect this is a strange combination which cannot be reached from
> userspace.

I mean, via nft.