In modern OS (Linux, Windows 2000/XP, etc), all programs are separated in
terms of memory. So no process can access the memory of other processes
without specific methods. So no worry here.
The real nasty thing likes in the trick like that famous old article "Smash
the
stack for fun and profit" illustrated. And by far, this is still one of the
most
dominant security flaws in applications. So always using a valgrind to check
the program is a good practice.
On Mon, Oct 20, 2008 at 12:04 PM, Jehan <[EMAIL PROTECTED]> wrote:
> Forward to the list as it is a perfect answer!
>
> -------- Message original --------
> Sujet: Re: [Materm-devel] Small question about segfaults
> Date: Mon, 20 Oct 2008 16:40:14 +0200
> De: Frederik Deweerdt <[EMAIL PROTECTED]>
> Pour :: jehan <[EMAIL PROTECTED]>
> Références: <[EMAIL PROTECTED]>
> <[EMAIL PROTECTED]>
> <[EMAIL PROTECTED]>
>
> [replying to you in private, I can't post to the list right now]
> On Mon, Oct 20, 2008 at 04:35:06PM +0200, jehan wrote:
> > Frederik Deweerdt writes:
> >
> > > From the program's point of view, all memory space is his, some
> > > addresses are allocated, some not. But all the memory (eg. from 0 to
> > > 0xffffffff on a 32bits arch) is potentially his.
> >
> > Ok, so what I understand here is that you confirm that the program won't
> > segfault as long as I am not accessing another program's allocated
> memory,
> > even if I get out my own allocated memory. Is that so?
> Nope, if you get out your own allocated memory, you will segfault.
> ...but sometimes you won't :-)
>
> The trick is as illustrated by this sample program:
>
> int main()
> {
> char *p;
> int i;
> p = malloc(128); /* suppose that the libc allocated 4K for performance
> purposes here */
>
> for (i=0; i < 256; i++) {
> p[i] = '0';
> }
> return 0;
> }
>
> This could segfault or not, depending on what the call to malloc did
> behind the scenes.
> Luckily a tool like valgrind would catch this for you.
>
> Another point to clarify. From a program's point of view, he's alone
> running in his address space (0-0xffffffff). The kernel set the memory
> up in such a way.
>
> So there's no way you could access another program's memory (except for
> shared memory, like the one shmget provides)
>
> Regards,
> Frederik
>
>
>
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