bpf: Factor out visit_func_call_insn() in check_cfg()

During verifier check_cfg(), all instructions are
visited to ensure verifier can handle program control flows.
This patch factored out function visit_func_call_insn()
so it can be reused in later patch to visit callback function
calls. There is no functionality change for this patch.
Signed-off-by: NYonghong Song <yhs@fb.com>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>
Acked-by: NAndrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210226204920.3884136-1-yhs@fb.com

kernel/bpf/verifier.c

@@ -8592,6 +8592,27 @@ static int push_insn(int t, int w, int e, struct bpf_verifier_env *env,
 	return DONE_EXPLORING;
 }
 
+static int visit_func_call_insn(int t, int insn_cnt,
+				struct bpf_insn *insns,
+				struct bpf_verifier_env *env,
+				bool visit_callee)
+{
+	int ret;
+
+	ret = push_insn(t, t + 1, FALLTHROUGH, env, false);
+	if (ret)
+		return ret;
+
+	if (t + 1 < insn_cnt)
+		init_explored_state(env, t + 1);
+	if (visit_callee) {
+		init_explored_state(env, t);
+		ret = push_insn(t, t + insns[t].imm + 1, BRANCH,
+				env, false);
+	}
+	return ret;
+}
+
 /* Visits the instruction at index t and returns one of the following:
  *  < 0 - an error occurred
  *  DONE_EXPLORING - the instruction was fully explored
@@ -8612,18 +8633,8 @@ static int visit_insn(int t, int insn_cnt, struct bpf_verifier_env *env)
 		return DONE_EXPLORING;
 
 	case BPF_CALL:
-		ret = push_insn(t, t + 1, FALLTHROUGH, env, false);
-		if (ret)
-			return ret;
-
-		if (t + 1 < insn_cnt)
-			init_explored_state(env, t + 1);
-		if (insns[t].src_reg == BPF_PSEUDO_CALL) {
-			init_explored_state(env, t);
-			ret = push_insn(t, t + insns[t].imm + 1, BRANCH,
-					env, false);
-		}
-		return ret;
+		return visit_func_call_insn(t, insn_cnt, insns, env,
+					    insns[t].src_reg == BPF_PSEUDO_CALL);
 
 	case BPF_JA:
 		if (BPF_SRC(insns[t].code) != BPF_K)