Adjust the implementation of strncpy_s() for Linux

This change:
- prevents writing memory out of the range of the destination buffer
- prevents calling strlen() with non-null terminated c-string
- corrects the logic, which validates passed range to proceed
when real length fits the destination buffer

Related-To: NEO-7264
Signed-off-by: Wrobel, Patryk <patryk.wrobel@intel.com>

shared/source/helpers/string.h

@@ -31,28 +31,6 @@ inline int strcpy_s(char *dst, size_t dstSize, const char *src) { // NOLINT(read
     return 0;
 }
 
-inline int strncpy_s(char *dst, size_t numberOfElements, const char *src, size_t count) { // NOLINT(readability-identifier-naming)
-    if ((dst == nullptr) || (src == nullptr)) {
-        return -EINVAL;
-    }
-    if (numberOfElements < count) {
-        return -ERANGE;
-    }
-
-    size_t length = strlen(src);
-    if (length > count) {
-        length = count;
-    }
-    memcpy(dst, src, length);
-
-    if (length < numberOfElements) {
-        numberOfElements = length;
-    }
-    dst[numberOfElements] = '\0';
-
-    return 0;
-}
-
 inline size_t strnlen_s(const char *str, size_t count) { // NOLINT(readability-identifier-naming)
     if (str == nullptr) {
         return 0;
@@ -66,6 +44,22 @@ inline size_t strnlen_s(const char *str, size_t count) { // NOLINT(readability-i
     return count;
 }
 
+inline int strncpy_s(char *dst, size_t numberOfElements, const char *src, size_t count) { // NOLINT(readability-identifier-naming)
+    if ((dst == nullptr) || (src == nullptr)) {
+        return -EINVAL;
+    }
+
+    size_t length = strnlen_s(src, count);
+    if (numberOfElements <= count && numberOfElements <= length) {
+        return -ERANGE;
+    }
+
+    memcpy(dst, src, length);
+    dst[length] = '\0';
+
+    return 0;
+}
+
 inline int memcpy_s(void *dst, size_t destSize, const void *src, size_t count) { // NOLINT(readability-identifier-naming)
     if ((dst == nullptr) || (src == nullptr)) {
         return -EINVAL;

shared/test/unit_test/helpers/string_tests.cpp

@@ -27,7 +27,7 @@ TEST(StringHelpers, GivenParamsWhenUsingStrncpyThenReturnIsCorrect) {
     ret = strncpy_s(dst, 1024, nullptr, 1024);
     EXPECT_EQ(ret, -EINVAL);
 
-    ret = strncpy_s(dst, 512, src, 1024);
+    ret = strncpy_s(dst, 10, src, 1024);
     EXPECT_EQ(ret, -ERANGE);
 
     memset(dst, 0, sizeof(dst));
@@ -37,19 +37,41 @@ TEST(StringHelpers, GivenParamsWhenUsingStrncpyThenReturnIsCorrect) {
     for (size_t i = strlen(src) / 2; i < sizeof(dst); i++)
         EXPECT_EQ(0, dst[i]);
 
-    memset(dst, 0, sizeof(dst));
-    ret = strncpy_s(dst, strlen(src) / 2, src, strlen(src) / 2);
-    EXPECT_EQ(ret, 0);
-    EXPECT_EQ(0, memcmp(dst, src, strlen(src) / 2));
-    for (size_t i = strlen(src) / 2; i < sizeof(dst); i++)
-        EXPECT_EQ(0, dst[i]);
+    ret = strncpy_s(dst, 1024, src, 1024);
+    ASSERT_EQ(0, ret);
 
-    strncpy_s(dst, 1024, src, 1024);
     EXPECT_EQ(0, memcmp(dst, src, strlen(src)));
     for (size_t i = strlen(src); i < sizeof(dst); i++)
         EXPECT_EQ(0, dst[i]);
 }
 
+TEST(StringHelpers, GivenCountGreaterEqualToNumberOfElementsThenReturnErangeAndSetFirstStringToNullTerminator) {
+    // strncpy_s() copies at most COUNT bytes and appends null-terminator at dst[COUNT].
+    // It means, that for given COUNT, at least COUNT+1 bytes are required in dst buffer.
+
+    const size_t firstWordLength = 9;
+    char src[] = "c-strings are serious business!";
+
+    char dst[firstWordLength] = {'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i'};
+    const auto ret = strncpy_s(dst, sizeof(dst), src, firstWordLength);
+
+    EXPECT_EQ(-ERANGE, ret);
+}
+
+TEST(StringHelpers, GivenNotNullTerminatedSourceThenCopyAtMostCountBytesAndAppendNulltermination) {
+    // If null-terminator is missing, then strncpy_s() copies COUNT bytes and stores it at dst[COUNT].
+
+    const size_t srcLength = 8;
+    char src[srcLength] = {'c', '-', 's', 't', 'r', 'i', 'n', 'g'};
+
+    const size_t nullterminatorLength = 1;
+    char dst[srcLength + nullterminatorLength] = {'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i'};
+    const auto ret = strncpy_s(dst, sizeof(dst), src, srcLength);
+
+    ASSERT_EQ(0, ret);
+    EXPECT_STREQ("c-string", dst);
+}
+
 TEST(StringHelpers, GivenParamsWhenUsingMemmoveThenReturnIsCorrect) {
     char dst[1024] = "";
     char src[1024] = "HelloWorld";