[SOLVED] command line args buffer overflow

doughyi8u · 03-29-2016, 11:24 AM

I'm a novice c programmer and have read about buffer overflows in programs. This may sound like a dumb question but what's the prevent a buffer overflow from command line args? What prevents this if my assumption is incorrect?

HMW · 03-29-2016, 11:43 AM

Quote:

Originally Posted by doughyi8u

I'm a novice c programmer and have read about buffer overflows in programs. This may sound like a dumb question but what's the prevent a buffer overflow from command line args? What prevents this if my assumption is incorrect?

You "prevent" buffer overflow by not allowing them to happen. In other words; make d*mn sure that you don't allow things to be written where it should not.

But, if you're wondering if you can have too many arguments, as in:

Code:

int main (int argc, char *argv[])   //  command line arguments

the short answer is no. It all boils down to the programmer, as in what he/she does with the arguments.

Best regards,
HMW

NevemTeve · 03-29-2016, 11:46 AM

Command line arguments are 'dealt with' by the time your program starts. Of course you can still do stupid things in your program, eg:

Code:

    char copy0buff [64];
    strcpy (copy0buff, argv[0]);

fix:

Code:

    char *copy0buff;
    copy0buff= strdup (argv[0]);

dugan · 03-29-2016, 12:32 PM

Quote:

Originally Posted by doughyi8u

I'm a novice c programmer and have read about buffer overflows in programs. This may sound like a dumb question but what's the prevent a buffer overflow from command line args? What prevents this if my assumption is incorrect?

Well, what is your assumption?

How do you think "a buffer overflow from command line args" would be done?

doughyi8u · 03-29-2016, 01:40 PM

My assumption is that you could cause a buffer overflow by using command line args. Is that not possible?

rknichols · 03-29-2016, 01:48 PM

If you're talking about the command line arguments that your program receives, that is not space that your program allocates or has any control over. The space for your program's arguments and environment is set up by the execve() system call in the program that invokes yours, and a limit on the total size is enforced at that time.

From /usr/include/linux/limits.h:

Code:

#define ARG_MAX       131072    /* # bytes of args + environ for exec() */

Of course if your program modifies its argument strings, it is up to you not to exceed the space that they originally used.

doughyi8u · 03-29-2016, 02:08 PM

thanks rknichols. that answered my question