Never trust a pointer parameter (especially strings)

 

Recently I was working on an API which took a string as one of the parameters. The code did something like

 

1 STDAPI FooBarAPI(LPCWSTR pszArg)
2 {
3      bool fOpAllowed = IsSomeOpAllowed(pszArg);
4  
5      if (true == fOpAllowed)
6      {
7         DoSomeOp(pszArg);
8      }
9 }

 

Now, there was a security issue (or inconsistency depending on what you are doing) lurking in this API. I shouldnt be performing an action based on a decision using the string passed to me. Why? Since there is a window of oppurtunity between 3 & 7 when the caller could change what pszArg points to. Its always recommended to copy pointer data into a local copy before performing any action since that gaurantees you that the data cannot be changed in the middle of your function.