I am practicing my heap exploit skill with following website.
http://hatriot.github.io/blog/2014/09/21/protostar-heap-exploits/. But under the title of heap 3 exploit, I didnot understand with what it does.
(gdb) r AAAA$(python -c 'print "A"*28 + "\xfc\xff\xff\xff" + "\xfc\xff\xff\xff"') $(python -c 'print "\x41"*4 + "\x1c\xb1\x04\x08" + "\x0c\xc0\x04\x08"') CCCC
It is exploiting metadata of heap.I understand first argument which overflow Prev_size and size of chunk B.But in second argument,why he starts with 'B'*4 .Why? I think it should follow fd and bk.Please explain me.Thank you