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

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Message-ID: <CANn89iL6DA3Gha1h8uje5U5rObnKCOrF360Q-U1bGaDCmm3wWQ@mail.gmail.com>
Date: Thu, 22 Aug 2024 08:39:56 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: Pablo Neira Ayuso <pablo@...filter.org>
Cc: netfilter-devel@...r.kernel.org, davem@...emloft.net, 
	netdev@...r.kernel.org, kuba@...nel.org, pabeni@...hat.com, fw@...len.de
Subject: Re: [PATCH net 3/3] netfilter: flowtable: validate vlan header

On Thu, Aug 22, 2024 at 2:17 AM Pablo Neira Ayuso <pablo@...filter.org> 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: syzbot+8407d9bb88cd4c6bf61a@...kaller.appspotmail.com
> Signed-off-by: Pablo Neira Ayuso <pablo@...filter.org>
> ---
>  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.