net: cls_bpf: fix NULL deref on offload filter removal

Commit 4011921 ("net: sched: refactor block offloads counter
usage") missed the fact that either new prog or old prog may be
NULL.

Fixes: 4011921 ("net: sched: refactor block offloads counter usage")
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/cls_bpf.c

@@ -162,16 +162,20 @@ static int cls_bpf_offload_cmd(struct tcf_proto *tp, struct cls_bpf_prog *prog,
 	cls_bpf.name = obj->bpf_name;
 	cls_bpf.exts_integrated = obj->exts_integrated;
 
-	if (oldprog)
+	if (oldprog && prog)
 		err = tc_setup_cb_replace(block, tp, TC_SETUP_CLSBPF, &cls_bpf,
 					  skip_sw, &oldprog->gen_flags,
 					  &oldprog->in_hw_count,
 					  &prog->gen_flags, &prog->in_hw_count,
 					  true);
-	else
+	else if (prog)
 		err = tc_setup_cb_add(block, tp, TC_SETUP_CLSBPF, &cls_bpf,
 				      skip_sw, &prog->gen_flags,
 				      &prog->in_hw_count, true);
+	else
+		err = tc_setup_cb_destroy(block, tp, TC_SETUP_CLSBPF, &cls_bpf,
+					  skip_sw, &oldprog->gen_flags,
+					  &oldprog->in_hw_count, true);
 
 	if (prog && err) {
 		cls_bpf_offload_cmd(tp, oldprog, prog, extack);