Subject: Re: [PATCH net 3/3] netfilter: flowtable: validate vlan header

From: Pablo Neira Ayuso <[email-masked]>
Date: Thu, 22 Aug 2024 12:21:29 +0200

On Thu, Aug 22, 2024 at 08:39:56AM +0200, Eric Dumazet wrote:
> On Thu, Aug 22, 2024 at 2:17 AM Pablo Neira Ayuso <[email-masked]> wrote:
> >
> > Ensure there is sufficient room to access the protocol field of the
> > VLAN header, validate it once before the flowtable lookup.
> >
> > =====================================================
> > BUG: KMSAN: uninit-value in nf_flow_offload_inet_hook+0x45a/0x5f0 net/netfilter/nf_flow_table_inet.c:32
> >  nf_flow_offload_inet_hook+0x45a/0x5f0 net/netfilter/nf_flow_table_inet.c:32
> >  nf_hook_entry_hookfn include/linux/netfilter.h:154 [inline]
> >  nf_hook_slow+0xf4/0x400 net/netfilter/core.c:626
> >  nf_hook_ingress include/linux/netfilter_netdev.h:34 [inline]
> >  nf_ingress net/core/dev.c:5440 [inline]
> >
> > Fixes: 4cd91f7c290f ("netfilter: flowtable: add vlan support")
> > Reported-by: [email-masked]
> > Signed-off-by: Pablo Neira Ayuso <[email-masked]>
> > ---
> >  net/netfilter/nf_flow_table_inet.c | 3 +++
> >  net/netfilter/nf_flow_table_ip.c   | 3 +++
> >  2 files changed, 6 insertions(+)
> >
> > diff --git a/net/netfilter/nf_flow_table_inet.c b/net/netfilter/nf_flow_table_inet.c
> > index 88787b45e30d..dd9a392052ee 100644
> > --- a/net/netfilter/nf_flow_table_inet.c
> > +++ b/net/netfilter/nf_flow_table_inet.c
> > @@ -17,6 +17,9 @@ nf_flow_offload_inet_hook(void *priv, struct sk_buff *skb,
> >
> >         switch (skb->protocol) {
> >         case htons(ETH_P_8021Q):
> > +               if (!pskb_may_pull(skb, VLAN_HLEN))
> > +                       return NF_ACCEPT;
> > +
> >                 veth = (struct vlan_ethhdr *)skb_mac_header(skb);
> 
> Is skb_mac_header(skb) always pointing at skb->data - 14 at this stage ?
> 
> Otherwise, using
> 
>   if (!pskb_may_pull(skb, skb_mac_offset(skb) + sizeof(*veth))  would be safer.

That looks consistent. Done and I just sent a new PR. Thanks.