There is no hardware supporting ct helper offload. However, prior to this
patch, a flower filter with a helper in the ct action can be successfully
set into the HW, for example (eth1 is a bnxt NIC):

  # tc qdisc add dev eth1 ingress_block 22 ingress
  # tc filter add block 22 proto ip flower skip_sw ip_proto tcp \
    dst_port 21 ct_state -trk action ct helper ipv4-tcp-ftp
  # tc filter show dev eth1 ingress

    filter block 22 protocol ip pref 49152 flower chain 0 handle 0x1
      eth_type ipv4
      ip_proto tcp
      dst_port 21
      ct_state -trk
      skip_sw
      in_hw in_hw_count 1   <----
        action order 1: ct zone 0 helper ipv4-tcp-ftp pipe
         index 2 ref 1 bind 1
        used_hw_stats delayed

This might cause the flower filter not to work as expected in the HW.

This patch avoids this problem by simply returning -EOPNOTSUPP in
tcf_ct_offload_act_setup() to not allow to offload flows with a helper
in act_ct.

Fixes: a21b06e73191 ("net: sched: add helper support in act_ct")
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Reviewed-by: Jamal Hadi Salim <jhs@mojatatu.com>
Link: https://lore.kernel.org/r/f8685ec7702c4a448a1371a8b34b43217b583b9d.1699898008.git.lucien.xin@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>