From d790cc6a50e7e54bc0fe288905ee9660ab43fb44 Mon Sep 17 00:00:00 2001
From: stdpain <34912776+stdpain@users.noreply.github.com>
Date: Thu, 3 Jun 2021 18:38:10 +0800
Subject: [PATCH] [BUG] Fixed the problem that substring function may access
 illegal address (#5952)

---
 be/src/exprs/string_functions.cpp       | 2 +-
 be/test/exprs/string_functions_test.cpp | 3 +++
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/be/src/exprs/string_functions.cpp b/be/src/exprs/string_functions.cpp
index 262e7f0bb7..26486cdd96 100644
--- a/be/src/exprs/string_functions.cpp
+++ b/be/src/exprs/string_functions.cpp
@@ -69,7 +69,7 @@ StringVal StringFunctions::substring(FunctionContext* context, const StringVal&
     if (str.is_null || pos.is_null || len.is_null || pos.val > str.len) {
         return StringVal::null();
     }
-    if (len.val <= 0 || str.len == 0) {
+    if (len.val <= 0 || str.len == 0 || pos.val == 0) {
         return StringVal();
     }
 
diff --git a/be/test/exprs/string_functions_test.cpp b/be/test/exprs/string_functions_test.cpp
index 92c92e71e4..c0fd49f630 100644
--- a/be/test/exprs/string_functions_test.cpp
+++ b/be/test/exprs/string_functions_test.cpp
@@ -291,6 +291,9 @@ TEST_F(StringFunctionsTest, null_or_empty) {
 
 TEST_F(StringFunctionsTest, substring) {
     doris_udf::FunctionContext* context = new doris_udf::FunctionContext();
+    
+    ASSERT_EQ(AnyValUtil::from_string_temp(context, std::string("")),
+              StringFunctions::substring(context, StringVal("hello word"), 0, 5));
 
     ASSERT_EQ(AnyValUtil::from_string_temp(context, std::string("hello")),
               StringFunctions::substring(context, StringVal("hello word"), 1, 5));