Merge pull request #307 from ethereum/loader_strcpy_s

loader: Fix strcpy_s()

lib/loader/loader.c

@@ -42,18 +42,33 @@
 #define ATTR_FORMAT(...)
 #endif
 
-#if !_WIN32
+#if _WIN32
+#define strcpy_sx strcpy_s
+#else
 /*
- * Provide strcpy_s() for GNU libc.
+ * Limited variant of strcpy_s().
+ *
+ * Provided for C standard libraries where strcpy_s() is not available.
  * The availability check might need to adjusted for other C standard library implementations.
  */
-static void strcpy_s(char* dest, size_t destsz, const char* src)
+#if !defined(EVMC_LOADER_MOCK)
+static
+#endif
+    int
+    strcpy_sx(char* restrict dest, size_t destsz, const char* restrict src)
 {
     size_t len = strlen(src);
-    if (len > destsz - 1)
-        len = destsz - 1;
+    if (len >= destsz)
+    {
+        // The input src will not fit into the dest buffer.
+        // Set the first byte of the dest to null to make it effectively empty string
+        // and return error.
+        dest[0] = 0;
+        return 1;
+    }
     memcpy(dest, src, len);
     dest[len] = 0;
+    return 0;
 }
 #endif
 
@@ -124,7 +139,7 @@ evmc_create_fn evmc_load(const char* filename, enum evmc_loader_error_code* erro
     const char prefix[] = "evmc_create_";
     const size_t prefix_length = strlen(prefix);
     char prefixed_name[sizeof(prefix) + PATH_MAX_LENGTH];
-    strcpy_s(prefixed_name, sizeof(prefixed_name), prefix);
+    strcpy_sx(prefixed_name, sizeof(prefixed_name), prefix);
 
     // Find filename in the path.
     const char* sep_pos = strrchr(filename, '/');
@@ -142,7 +157,7 @@ evmc_create_fn evmc_load(const char* filename, enum evmc_loader_error_code* erro
         name_pos += lib_prefix_length;
 
     char* base_name = prefixed_name + prefix_length;
-    strcpy_s(base_name, PATH_MAX_LENGTH, name_pos);
+    strcpy_sx(base_name, PATH_MAX_LENGTH, name_pos);
 
     // Trim the file extension.
     char* ext_pos = strrchr(prefixed_name, '.');

test/unittests/test_loader.cpp

@@ -16,6 +16,13 @@ static constexpr bool is_windows = false;
 #endif
 
 extern "C" {
+#if _WIN32
+#define strcpy_sx strcpy_s
+#else
+/// Declaration of internal function defined in loader.c.
+int strcpy_sx(char* dest, size_t destsz, const char* src);
+#endif
+
 /// The library path expected by mocked evmc_test_load_library().
 extern const char* evmc_test_library_path;
 
@@ -118,6 +125,28 @@ static evmc_instance* create_failure()
     return nullptr;
 }
 
+TEST_F(loader, strcpy_sx)
+{
+    const char input_empty[] = "";
+    const char input_that_fits[] = "x";
+    const char input_too_big[] = "12";
+    char buf[2] = {0x0f, 0x0f};
+    static_assert(sizeof(input_empty) <= sizeof(buf), "");
+    static_assert(sizeof(input_that_fits) <= sizeof(buf), "");
+    static_assert(sizeof(input_too_big) > sizeof(buf), "");
+
+    EXPECT_EQ(strcpy_sx(buf, sizeof(buf), input_empty), 0);
+    EXPECT_EQ(buf[0], 0);
+    EXPECT_EQ(buf[1], 0x0f);
+
+    EXPECT_EQ(strcpy_sx(buf, sizeof(buf), input_that_fits), 0);
+    EXPECT_EQ(buf[0], 'x');
+    EXPECT_EQ(buf[1], 0);
+
+    EXPECT_NE(strcpy_sx(buf, sizeof(buf), input_too_big), 0);
+    EXPECT_EQ(buf[0], 0);
+}
+
 TEST_F(loader, load_nonexistent)
 {
     constexpr auto path = "nonexistent";