net: sched: fix possible null pointer deref in tcf_block_put

We need to check block for being null in both tcf_block_put and
tcf_block_put_ext.

Fixes: 343723d ("net: sched: fix clsact init error path")
Reported-by: Prashant Bhole <[email protected]>
Signed-off-by: Jiri Pirko <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

Author: jpirko

net/sched/cls_api.c

@@ -379,6 +379,8 @@ void tcf_block_put(struct tcf_block *block)
 {
 	struct tcf_block_ext_info ei = {0, };
 
+	if (!block)
+		return;
 	tcf_block_put_ext(block, block->q, &ei);
 }