How to disable ASLR in Linux

Quick note to self on how to disable ASLR (address space layout randomization) in Ubuntu Linux:

$ sudo sh -c "echo 0 > /proc/sys/kernel/randomize_va_space"

Did you just email me back my own password?!

A while ago I wrote a blog post about what precautions to take handling password data on your website. plaintextoffenders.com is a website dedicated to this issue. It nicely points out why storing passwords in plaintext really is such a bad idea. The main part of the website is a pillory of submitted websites which obviously apply bad password practices. There's for awareness...

Seven Languages in Seven Weeks - Prolog Day 2 Self-Study

More fun with prolog! This self-study section consists in implementing some list operations.

Reverse the elements of a list

rev([], []).
rev([Head|Tail], List) :- append(X, [Head], List), rev(Tail, X).

Find the smallest element of a list.

min([X], X).
min([Head1|[Head2|Tail]], X) :- Head1 =< Head2, min([Head1|Tail], X).
min([Head1|[Head2|Tail]], X) :- Head1 > Head2, min([Head2|Tail], X).

Sort the elements of a list.

insert(X, [], [X]).
insert(X, [H|T], [X,H|T]) :- X =< H.
insert(X, [H|T], [H|Rest]) :- X > H, insert(X, T, Rest).

isort([], Acc, Acc).
isort([H|T], Acc, Sorted) :- insert(H, Acc, Acc2), isort(T, Acc2, Sorted).

Seven Languages in Seven Weeks - Prolog Day 1 Self-Study

For this book's section about prolog, I'll be using SWI-Prolog, as I'm currently getting an error installing the gnu-prolog macport. Here's the link to the SWI-Prolog online reference.

Make a simple knowledge base. Represent some of your favorite books and authors.

% books.pl
book(sevenLanguagesInSevenWeeks).
book(cleanCode).
book(cleanCoder).
book(programmingInScala).
author(odersky).
author(tate).
author(martin).
wrote(odersky, programmingInScala).
wrote(tate, sevenLanguagesInSevenWeeks).
wrote(martin, cleanCode).
wrote(martin, cleanCoder).

Find all books in your knowledge base written by one author.

?- ['books'].
% books compiled 0.00 sec, 13 clauses
true.

?- wrote(martin, X).
X = cleanCode ;
X = cleanCoder.

Make a knowledge base representing musicians and instruments. Also represent musicians and their genre of music.

% music.pl
instrument(flea, bass).
instrument(hendrix, guitar).
instrument(hancock, piano).
instrument(cash, guitar).
genre(flea, funk).
genre(hendrix, blues).
genre(hancock, jazz).
genre(cash, country).

Find all musicians who play the guitar.

?- ['music'].
% music compiled 0.00 sec, 10 clauses
true.

?- instrument(X, guitar).
X = hendrix ;
X = cash.

How to get a List of Installed JVMs on a Mac

I got this tip from a fellow worker:

$ /usr/libexec/java_home -V

This command will get you the list of installed Java Virtual Machines installed on your Mac OS X system.

Inspecting the Process Environment Variables with GDB

While trying to solve the 4th level of the vortex wargame, I found it was necessary to learn how to inspect the location and content of the environment variables within the process memory.

GDB has built-in commands to inspect the process environment, see the GDB manual. You can either list all environment variables or a specific one (e.g. FOOBAR) using the following commands, which will output their values:

(gdb) show environment
(gdb) show environment FOOBAR

In order to locate the environment variables within the process memory, you can query the variable char** environ (see the libc reference and this entry on stack overflow):

(gdb) x/s *((char **)environ)

This will print the location of the first environment variable and its representation as string. To print the next variables, simply add an offset to the variable:

(gdb) x/s *((char **)environ + 1)

I also found these links to be useful:

• GDB macros by IBM developers resources
• Some more GDB tips & tricks

Seven Languages in Seven Weeks - Io Day 3 Self-Study

It's been some time now, still I'm keeping up reading Seven Languages in Seven Weeks. Here's the last self-study section about the Io programming language.

Enhance the XML program to add spaces to show the indentation structure.

Builder := Object clone
Builder numIndents := 0
Builder doIndents := method (for (i, 1, numIndents, write(" ")))
Builder openTag := method(name, doIndents; writeln("<", name, ">"))
Builder closeTag := method(name, doIndents; writeln("</", name, ">"))
Builder forward := method (
  openTag(call message name);
  numIndents = numIndents + 1;
  call message arguments foreach (
    arg,
    content := self doMessage(arg);
    if (content type == "Sequence", doIndents; writeln(content))
  );
  numIndents = numIndents - 1;
  closeTag(call message name)
)

Builder ul(
  li("Javascript"),
  li("Lua"),
  li("Javascript")
)

Create a list syntax that uses brackets

squareBrackets := method(call message arguments)

Enhance the XML program to handle attributes: if the first argument is a map (use the curly brackets syntax), add attributes to the XML program. For example: book({"author": "Tate"}...) would print <book author="Tate">.

OperatorTable addAssignOperator(":", "atPutNumber")
Map atPutNumber := method(
  self atPut(
    call evalArgAt(0) asMutable removePrefix("\"") removeSuffix("\""),
    call evalArgAt(1)
  )
)
curlyBrackets := method(
  map := Map clone;
  call message arguments foreach(arg, map doMessage(arg));
  map
)

Builder := Object clone
Builder numIndents := 0
Builder doIndents := method (for (i, 1, numIndents, write(" ")))
Builder doAttributes := method(map, map keys foreach(key, write(" ", key, "=\"", map at(key) ,"\"")))
Builder forward := method (
  doIndents; write("<", call message name);
  if(call message arguments size == 0, writeln(">"));
  numIndents = numIndents + 1;
  call message arguments foreach (i, arg,
    content := self doMessage(arg);
    if (i == 0, 
      if(content type == "Map", doAttributes(content));
      writeln(">")
    )
    if (content type == "Sequence", doIndents; writeln(content));
  );
  numIndents = numIndents - 1;
  doIndents; writeln("</", call message name, ">")
)