What to Inject
Part 1: 8 bytes of junk
Overwritten by the first free() when it adds a prev_size and size field before the chunk is added to the bins
Part 2: \xeb\x0c
Assembler for jumping ahead 12 bytes
Part 3: 12 bytes of junk to be jumped over
Part 4: Shellcode
Part 5: Filler to fill up first buffer within 4 bytes of the end of the buffer