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Extract sequences of bytes from binary for differents blocks

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# 50  
Old 09-03-2013
Can you provide the output of gdb <binary> <core> with backtrace?

--ahamed
# 51  
Old 09-03-2013
Hello ahamed,

<Binary> would be the binary file?

<Core> what should be core?

Send this command will generate the backtrace?
# 52  
Old 09-03-2013
Just gave this code another look over for you, and there still a slight chance of buffer overflow if a sub block is between 252 and 255 bytes.

We should also increase the buffer to 259 chars or test for len > 251 in the below code segment:

Code:
                 if(len > 255) {
                     fprintf(stderr, "Len overflow: %d\n", len);
                     return 1;
                 }

This is due to the fread starting at ptr+3
# 53  
Old 09-03-2013
Hello Chubler_XL,

Thanks for the help.

I've changed from len>255 to len >259 but still happens the same issue.
Code:
if(len > 259) { 
    fprintf(stderr, "Len overflow: %d\n", len);
    return 1;
}

And I've sent the gdb in the way below but I get error shown.
Code:
gdb binary script.exe.stackdump
 
"/cygdrive/c/Script/binary: not in executable format: File format not recognized
"/cygdrive/c/Script/script.exe.stackdump" is not a core dump: File format not recognized

Regards
Last edited by Ophiuchus; 09-03-2013 at 08:52 PM..
# 54  
Old 09-03-2013
No, that change won't help.

Either change the test to if (len > 251) {

OR change the buffer size to unsigned char buf[259];
# 55  
Old 09-03-2013
Hello Chubler_XL,

I've tried changing both options, one first and I tested and the same result, then
I changed only the buff[259] and the same problem.

I've done and hexdump and verified the block where the script stops, and I compared with the previos block that was processed succesfully and the differences are not to big, but are as follow:
Code:
For the last block processed correctly:
From 0x32 (begin) to end of block--> 442  bytes
From 0xff 0x34 (begin of sub-block) to end of block --> 327 bytes

For the block where the program stops:	
From 0x32(begin) to end of block --> 454 bytes
From 0xff 0x34(begin of sub-block) to end of block --> 328 bytes

Do you think this could be the issue? which buffer setting could be good to handle this block sligthly bigger?

Thanks in advance
# 56  
Old 09-03-2013
Be carefull, when a C program crashes like that you will usually have unwritten bytes in io buffers. Call fflush(stdout); after any printf to ensure you see the latest output.
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