Re: [nf-next PATCH] netfilter: nft_exthdr: Search chunks in SCTP packets only

[Phil Sutter <phil@nwl.cc>]

On Thu, Jun 10, 2021 at 07:43:34PM +0200, Pablo Neira Ayuso wrote:
> On Thu, Jun 10, 2021 at 04:23:16PM +0200, Phil Sutter wrote:
> > Since user space does not generate a payload dependency, plain sctp
> > chunk matches cause searching in non-SCTP packets, too. Avoid this
> > potential mis-interpretation of packet data by checking pkt->tprot.
> > 
> > Fixes: 133dc203d77df ("netfilter: nft_exthdr: Support SCTP chunks")
> > Signed-off-by: Phil Sutter <phil@nwl.cc>
> > ---
> >  net/netfilter/nft_exthdr.c | 5 ++++-
> >  1 file changed, 4 insertions(+), 1 deletion(-)
> > 
> > diff --git a/net/netfilter/nft_exthdr.c b/net/netfilter/nft_exthdr.c
> > index 7f705b5c09de8..1093bb83f8aeb 100644
> > --- a/net/netfilter/nft_exthdr.c
> > +++ b/net/netfilter/nft_exthdr.c
> > @@ -312,6 +312,9 @@ static void nft_exthdr_sctp_eval(const struct nft_expr *expr,
> >  	const struct sctp_chunkhdr *sch;
> >  	struct sctp_chunkhdr _sch;
> >  
> > +	if (!pkt->tprot_set || pkt->tprot != IPPROTO_SCTP)
> > +		goto err;
> 
> nft_set_pktinfo_unspec() already initializes pkt->tprot to zero.
> 
> I think it's safe to simplify this to:
> 
> 	if (pkt->tprot != IPPROTO_SCTP)

Are you sure? Checking the spots that (should) initialize
tprot/tprot_set, in nft_do_chain_inet() it seems that if state->pf is
neither NFPROTO_IPV4 nor NFPROTO_IPV6, nft_do_chain() is called without
prior init. Maybe default case should call nft_set_pktinfo_unspec()?

BTW: The final return call in nft_do_chain_inet_ingress() is dead code,
right?

Thanks, Phil