bpf: teach verifier to track stack depth

teach verifier to track bpf program stack depth

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 6bb38d7..fcc80ca 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -171,6 +171,7 @@
 	atomic_t refcnt;
 	u32 used_map_cnt;
 	u32 max_ctx_offset;
+	u32 stack_depth;
 	struct latch_tree_node ksym_tnode;
 	struct list_head ksym_lnode;
 	const struct bpf_verifier_ops *ops;