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Re: Stackoverflow, and how C uses stack to remember function calls

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On 3/4/17 15:30, David Brown wrote:
> On 04/03/17 12:40, Alla wrote:
>> Hello!
>>
>> One of the lectures touched upon the following:
>>
>> Before writing my question, I would like to say that I might have not
>> correctly written down the material, so it might sound incorrect, to say
>> the least; therefore, please, correct what I will write now and help me
>> to understand how it works, maybe with the help of some functions
>> (please, nothing too fancy and complicated). Please, read to the end
>> before answering because it might not be clear what I would like to ask
>> about and thus to understand.
>>
>> Below is an example a completely incorrect code that doesn't perform any
>> error checking, and used for illustration purpose. This program will
>> "blindly" copy one string into another. If the length of bar exceeds the
>> length of c, then something longer than allocated memory on stack will
>> creep into c's return address space (almost quoting), and worse yet
>> (here starts the part I would like your help on) as C language secretly
>> uses stack also to remember when the function is called and what is the
>> address of the previous function called, a "bad guy" can "jump back" to
>> that function using swap() (not in the code below) in the main(), and
>> this swap() not only swaps local variables/arguments, but also make
>> main() return back to the function to execute it; thus a computer
>> blindly assumes that bytes in that "address" part are the address to
>> which it should return. Therefore, these bytes might be some other,
>> rogue address, which the "bad guy" wants the program to go to - sort of
>> tricking the system. And this is done by copying more elements into the
>> c array.
>>
>> #include <stdio.h>
>> #include <string.h>
>>
>> void f(char *bar)
>> {
>>    char c[12];
>>    strncpy(c, bar, strlen(bar));
>> }
>>
>> int main (int argc, char **argv)
>> {
>>    f(argv[1]);
>> }
>>
>> How does this "redirection" happen, and what is actually happening
>> underneath the hood? As I understand it, when the program is compiled,
>> first a memory for
>> int main() with its local variables is allocated on the stack; if we
>> assume that a stack is a vertically placed rectangle, then the memory
>> block for the main function will be at the bottom. Next, as main()
>> contains a call to function f(), the memory for f and its local
>> variables is allocated "above" the memory for main(). When the program
>> is executed, once f() is called and finished its job, the memory on
>> stack is "cleared". So how that redirection can happen?
>>
>> Thank you very much!
>
> A good place to look would be the Wikipedia article - which looks like
> the source for your lecturer's example!
>
> <https://en.wikipedia.org/wiki/Stack_buffer_overflow>
>
>
> There are many other websites that explain the basic idea (though it is
> not always easy to guess which websites might give a good explanation).
>
> <https://arstechnica.com/security/2015/08/how-security-flaws-work-the-buffer-overflow/>
Thank you very much. I will study these materials. Indeed, web is 
inundated with different explanations, but I would rather come here for 
advises and help because I trust this community.


Respectfully,

Alla

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Stackoverflow, and how C uses stack to remember function calls Alla <vitale.alla@gmail.com> - 2017-03-04 14:40 +0300
  Re: Stackoverflow, and how C uses stack to remember function calls Malcolm McLean <malcolm.mclean5@btinternet.com> - 2017-03-04 03:53 -0800
    Re: Stackoverflow, and how C uses stack to remember function calls Alla <vitale.alla@gmail.com> - 2017-03-04 14:58 +0300
      Re: Stackoverflow, and how C uses stack to remember function calls Malcolm McLean <malcolm.mclean5@btinternet.com> - 2017-03-04 04:04 -0800
        Re: Stackoverflow, and how C uses stack to remember function calls Alla <vitale.alla@gmail.com> - 2017-03-04 15:12 +0300
    Re: Stackoverflow, and how C uses stack to remember function calls mark.bluemel@gmail.com - 2017-03-06 00:41 -0800
  Re: Stackoverflow, and how C uses stack to remember function calls David Brown <david.brown@hesbynett.no> - 2017-03-04 13:30 +0100
    Re: Stackoverflow, and how C uses stack to remember function calls Alla <vitale.alla@gmail.com> - 2017-03-04 15:34 +0300
      Re: Stackoverflow, and how C uses stack to remember function calls David Brown <david.brown@hesbynett.no> - 2017-03-04 15:23 +0100
        Re: Stackoverflow, and how C uses stack to remember function calls Alla <vitale.alla@gmail.com> - 2017-03-04 18:22 +0300
          Re: Stackoverflow, and how C uses stack to remember function calls Chad <cdalten@gmail.com> - 2017-03-04 07:53 -0800
        Re: Stackoverflow, and how C uses stack to remember function calls Alla <vitale.alla@gmail.com> - 2017-03-04 19:29 +0300
  Re: Stackoverflow, and how C uses stack to remember function calls "James R. Kuyper" <jameskuyper@verizon.net> - 2017-03-04 11:18 -0500
    Re: Stackoverflow, and how C uses stack to remember function calls Alla <vitale.alla@gmail.com> - 2017-03-04 20:10 +0300
      Re: Stackoverflow, and how C uses stack to remember function calls "James R. Kuyper" <jameskuyper@verizon.net> - 2017-03-04 13:18 -0500
        Re: Stackoverflow, and how C uses stack to remember function calls Alla <vitale.alla@gmail.com> - 2017-03-04 22:43 +0300
    Re: Stackoverflow, and how C uses stack to remember function calls supercat@casperkitty.com - 2017-03-04 14:33 -0800
      Re: Stackoverflow, and how C uses stack to remember function calls Ian Collins <ian-news@hotmail.com> - 2017-03-05 11:50 +1300
        Re: Stackoverflow, and how C uses stack to remember function calls supercat@casperkitty.com - 2017-03-05 11:12 -0800
          Re: Stackoverflow, and how C uses stack to remember function calls Ian Collins <ian-news@hotmail.com> - 2017-03-06 17:11 +1300
            Re: Stackoverflow, and how C uses stack to remember function calls supercat@casperkitty.com - 2017-03-06 07:23 -0800
              Re: Stackoverflow, and how C uses stack to remember function calls David Brown <david.brown@hesbynett.no> - 2017-03-06 17:22 +0100
                Re: Stackoverflow, and how C uses stack to remember function calls scott@slp53.sl.home (Scott Lurndal) - 2017-03-06 16:40 +0000
                Re: Stackoverflow, and how C uses stack to remember function calls jm.bourguet@gmail.com - 2017-03-06 09:04 -0800
                Re: Stackoverflow, and how C uses stack to remember function calls scott@slp53.sl.home (Scott Lurndal) - 2017-03-06 17:18 +0000
                Re: Stackoverflow, and how C uses stack to remember function calls Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2017-03-06 11:22 -0700
                Re: Stackoverflow, and how C uses stack to remember function calls luser droog <luser.droog@gmail.com> - 2017-03-06 09:58 -0800
                Re: Stackoverflow, and how C uses stack to remember function calls luser droog <luser.droog@gmail.com> - 2017-03-06 10:04 -0800
  Re: Stackoverflow, and how C uses stack to remember function calls Barry Schwarz <schwarzb@dqel.com> - 2017-03-04 09:33 -0800
    Re: Stackoverflow, and how C uses stack to remember function calls Alla <vitale.alla@gmail.com> - 2017-03-04 22:46 +0300
  Re: Stackoverflow, and how C uses stack to remember function calls Keith Thompson <kst-u@mib.org> - 2017-03-04 12:25 -0800

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