Add NULL checks to fix possible undefined behavior (netty#10718)

Motivation:

In some situations we could have end up calling some functions with NULL parameters which in this case could lead to undefined behavior. All of this would have happened during loading of the native lib.

Modifications:

Add NULL check as guards and return early

Result:

Fix some possible undefined behavior

Author: normanmaurer

transport-native-unix-common/src/main/c/netty_unix_util.c

@@ -29,6 +29,10 @@ static const uint64_t NETTY_BILLION = 1000000000L;
 #endif /* NETTY_USE_MACH_INSTEAD_OF_CLOCK */
 
 char* netty_unix_util_prepend(const char* prefix, const char* str) {
+    if (str == NULL) {
+        // If str is NULL we should just return NULL as passing NULL to strlen is undefined behavior.
+        return NULL;
+    }
     char* result = NULL;
     if (prefix == NULL) {
         if ((result = (char*) malloc(sizeof(char) * (strlen(str) + 1))) == NULL) {
@@ -46,6 +50,10 @@ char* netty_unix_util_prepend(const char* prefix, const char* str) {
 }
 
 char* netty_unix_util_rstrstr(char* s1rbegin, const char* s1rend, const char* s2) {
+    if (s1rbegin == NULL || s1rend == NULL || s2 == NULL) {
+        // Return NULL if any of the parameters is NULL to not risk a segfault
+        return NULL;
+    }
     size_t s2len = strlen(s2);
     char *s = s1rbegin - s2len;
 
@@ -58,6 +66,11 @@ char* netty_unix_util_rstrstr(char* s1rbegin, const char* s1rend, const char* s2
 }
 
 static char* netty_unix_util_strstr_last(const char* haystack, const char* needle) {
+    if (haystack == NULL || needle == NULL) {
+        // calling strstr with NULL is undefined behavior. Better just return NULL and not risk a crash.
+        return NULL;
+    }
+
     char* prevptr = NULL;
     char* ptr = (char*) haystack;