On Thu, Aug 22, 2024 at 2:17 AM Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>
> ---
> 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.
