On 7/21/26 4:36 PM, Cen Zhang (Microsoft) wrote:
> When a packet arrives on an ARPHRD_NONE device (e.g. TUN),
> ovs_flow_key_extract() trusts the user-provided skb->protocol field: if
> it is ETH_P_TEB, the packet is classified as MAC_PROTO_ETHERNET and
> key_extract() is called without ensuring the skb has ETH_HLEN (14) bytes
> of linear data. key_extract() unconditionally pulls 2 * ETH_ALEN bytes
> for MAC addresses and parse_ethertype() pulls 2 more, either of which
> triggers a kernel BUG in __skb_pull() when the linear area is too small.
>
> kernel BUG at include/linux/skbuff.h:2848!
> RIP: 0010:key_extract+0xa7e/0xd90 net/openvswitch/flow.c:933
> ovs_flow_key_extract+0x419/0xa70
> ovs_vport_receive+0x222/0x390
> netdev_frame_hook+0x3e0/0x630
> tun_get_user+0x2d0c/0x38e0
>
> Fixed by adding check_header(skb, ETH_HLEN) in ovs_flow_key_extract()
> before calling key_extract().
>
> Fixes: 217ac77a3c25 ("openvswitch: allow L3 netdev ports")
> Reported-by: [email protected]
> Signed-off-by: Cen Zhang (Microsoft) <[email protected]>
> ---
> net/openvswitch/flow.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/net/openvswitch/flow.c b/net/openvswitch/flow.c
> index 66366982f604..a0f9d788d284 100644
> --- a/net/openvswitch/flow.c
> +++ b/net/openvswitch/flow.c
> @@ -1035,6 +1035,13 @@ int ovs_flow_key_extract(const struct ip_tunnel_info
> *tun_info,
> return res;
> key->mac_proto = res;
>
> + if (res == MAC_PROTO_ETHERNET) {
> + int err = check_header(skb, ETH_HLEN);
> +
> + if (unlikely(err))
> + return err;
> + }
I'd suggest moving this check closer to the place where we're pulling
the header, i.e. into the key_extract() function itself.
Best regards, Ilya Maximets.
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