Re: Usage of Secure C (memcpy_s, strcpy_s etc) functions on OpenSSL

Jordan Brown <openssl@xxxxxxxxxxxxxxxxxxxx> · Tue, 26 Nov 2019 23:47:20 +0000



    On 11/26/2019 7:41 AM, Michael Wojcik
      wrote:

    
        The Appendix K functions (memcpy_s, etc) do NOT "remove buffer
        overflow kind of issues completely", and anyone who thinks they
        do is making a serious error. The Appendix K functions impose an
        additional check. That's all they do. It is possible, and in
        some use cases quite easy, for the developer to pass the wrong
        value for the destsz parameter and invalidate that check.

      
        Some C experts have argued that the length-checking versions of
        the library functions, either the C90 ones such as strncat or
        the Appendix K ones, are essentially pointless anyway; that the
        caller needs to handle truncation and so ought to know whether
        truncation (or overflow) would occur before attempting the
        operation.

      
    I was initially a fan of them when I first heard of them, but have
    since soured on them, as have others.  They are very nearly useless
    for libraries, because their behavior is controlled on a
    process-global basis.  The library cannot assume that the "bad"
    cases will result in aborts, because the application might have
    chosen to have them return errors instead.  That means that the
    library has to check for and handle all of those "should be
    impossible" error cases.

    
    Here's a paper on the subject: 
    http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1967.htm

    -- 
Jordan Brown, Oracle ZFS Storage Appliance, Oracle Solaris