C Arrays and Memory Quiz

The following function is causing a memory violation. What line could not be responsible?
1 char *my_strdup(char *str)
2 {
3 int i;
4 char *str2 = malloc(strlen(str));
5 int length = strlen(str);
6 for(i = 0; i <= length; i++)
7 str2[i] = str[i];
8 str2[i] = '\0';
9 return str2;
10 }