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

[David Ahern <dsahern@kernel.org>]

On 9/29/22 9:21 AM, Florian Westphal wrote:
> 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...

Old usage is setting flow oif and it gets converted to the L3 device if
there is one. The new usage is flow l3mdev, but I only updated places I
new I was testing.

ie.., use l3mdev in the flow struct if you have a VRF test case for it.