Re: [PATCH 1/1] netfilter: nft_fib: Fix for rpath check with VRF devices

[Florian Westphal <fw@strlen.de>]

Guillaume Nault <gnault@redhat.com> wrote:

[ CC David Ahern ]

> On Wed, Sep 28, 2022 at 01:39:08PM +0200, Florian Westphal wrote:
> > From: Phil Sutter <phil@nwl.cc>
> > 
> > Analogous to commit b575b24b8eee3 ("netfilter: Fix rpfilter
> > dropping vrf packets by mistake") but for nftables fib expression:
> > Add special treatment of VRF devices so that typical reverse path
> > filtering via 'fib saddr . iif oif' expression works as expected.
> > 
> > Fixes: f6d0cbcf09c50 ("netfilter: nf_tables: add fib expression")
> > Signed-off-by: Phil Sutter <phil@nwl.cc>
> > Signed-off-by: Florian Westphal <fw@strlen.de>
> > ---
> >  net/ipv4/netfilter/nft_fib_ipv4.c | 3 +++
> >  net/ipv6/netfilter/nft_fib_ipv6.c | 6 +++++-
> >  2 files changed, 8 insertions(+), 1 deletion(-)
> > 
> > diff --git a/net/ipv4/netfilter/nft_fib_ipv4.c b/net/ipv4/netfilter/nft_fib_ipv4.c
> > index b75cac69bd7e..7ade04ff972d 100644
> > --- a/net/ipv4/netfilter/nft_fib_ipv4.c
> > +++ b/net/ipv4/netfilter/nft_fib_ipv4.c
> > @@ -83,6 +83,9 @@ void nft_fib4_eval(const struct nft_expr *expr, struct nft_regs *regs,
> >  	else
> >  		oif = NULL;
> >  
> > +	if (priv->flags & NFTA_FIB_F_IIF)
> > +		fl4.flowi4_oif = l3mdev_master_ifindex_rcu(oif);
> > +
> 
> Shouldn't we set .flowi4_l3mdev instead of .flowi4_oif?

No idea.
db53cd3d88dc328dea2e968c9c8d3b4294a8a674 sets both.
rp_filter modules in iptables only set flowi(6)_oif.

David, can you give advice on what the correct fix is?

Then we could change all users in netfilter at once rather than the
current collection of random-looking guesses...