[mapserver-dev] Ticket 3537 - Buffer overflow vulnerabilities

Yewondwossen Assefa yassefa at dmsolutions.ca
Wed Oct 6 13:45:19 EDT 2010

  On 06/10/2010 12:04 PM, Daniel Morissette wrote:
> Following up on this, Alan made some tests with GCC's "-ansi -pedantic"
> flags, and here is what we found:
> Daniel Morissette wrote:
>> Initializing a variable (and arrays) with a non-static value is not
>> valid in ANSI C (a.k.a. C89/90) and may not work on all compilers. I
>> know of at least VC++ on Windows that will fail.
>> i.e. the following pattern added in mapfile.c (and possibly elsewhere)
>>          size_t buffer_size = 10 + strlen(value+5) + 1;
>>   	char *init_string = (char*)malloc(buffer_size);
>> should be replaced with:
> [...]
> The code above is not reported as problematic by gcc -ansi -pedantic. So
> it seems that I was wrong in thinking that initializing a variable from
> a non-static value was invalid in C89/90. Nothing to change in Alan's
> patch for this.
>> I also noticed the following pattern in a few places. I don't know if
>> that's allowed or not in C89/90. Since bufferSize is a const that may be
>> okay, but I'm not 100% sure:
>>      const size_t bufferSize = 1024;
>>      char szBuffer[bufferSize];
> Unfortunately GCC reports this construct as invalid ("ISO C90 forbids
> variable length array"), even if bufferSize is a const.  :-(
> This construct is used in several places, so I still think we should
> wait for reports from someone testing with VC++ since it's the main
> compiler we support that doesn't support C99 extensions (such as
> variable length array declarations) and is likely the one that will
> dictate whether we can use this construct or not in the code.
Building with MSVC (9), I get build errors for the following declaration:
size_t buffer_size = 512;
  char buffer[buffer_size];  #line 2209

mappostgis.c(2209) : error C2057: expected constant expression
mappostgis.c(2209) : error C2466: cannot allocate an array of constant 
size 0
mappostgis.c(2209) : error C2133: 'buffer' : unknown size

  I will change locally and continue the build.

I also get build errors usually when variables are declared in the 
middle of the code and not at the beginning of functions or beginning of 
loops. I am not sure if it is a setting that I need to do or It is is 
simply not valid for all compilers. I tend to correct that when I build 
on windows.


Assefa Yewondwossen
Software Analyst

Email: yassefa at dmsolutions.ca

Phone: (613) 565-5056 (ext 14)
Fax:   (613) 565-0925

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