Add American Fuzzy Lop (afl) to third_party/afl/

third_party/afl/src/experimental/bash_shellshock/shellshock-fuzz.diff

+This patch shows a very simple way to find post-Shellshock bugs in bash, as
+discussed here:
+
+  http://lcamtuf.blogspot.com/2014/10/bash-bug-how-we-finally-cracked.html
+
+In essence, it shows a way to fuzz environmental variables. Instructions:
+
+1) Download bash 4.3, apply this patch, compile with:
+
+   CC=/path/to/afl-gcc ./configure
+   make clean all
+
+   Note that the harness puts the fuzzed output in $TEST_VARIABLE. With
+   Florian's Shellshock patch (bash43-028), this is no longer passed down
+   to the parser.
+
+2) Create and cd to an empty directory, put the compiled bash binary in
+   there, and run these commands:
+
+   mkdir in_dir
+   echo -n '() { a() { a; }; : >b; }' >in_dir/script.txt
+
+3) Run the fuzzer with:
+
+   /path/to/afl-fuzz -d -i in_dir -o out_dir ./bash -c :
+
+   The -d parameter is advisable only if the tested shell is fairly slow
+   or if you are in a hurry; will cover more ground faster, but
+   less systematically.
+
+4) Watch for crashes in out_dir/crashes/. Also watch for any new files
+   created in cwd if you're interested in non-crash RCEs (files will be
+   created whenever the shell executes "foo>bar" or something like
+   that). You can correlate their creation date with new entries in
+   out_dir/queue/.
+
+   You can also modify the bash binary to directly check for more subtle
+   fault conditions, or use the synthesized entries in out_dir/queue/
+   as a seed for other, possibly slower or more involved testing regimes.
+
+   Expect several hours to get decent coverage.
+
+--- bash-4.3/shell.c.orig       2014-01-14 14:04:32.000000000 +0100
++++ bash-4.3/shell.c    2015-04-30 05:56:46.000000000 +0200
+@@ -371,6 +371,14 @@
+   env = environ;
+ #endif /* __OPENNT */
+ 
++  {
++
++    static char val[1024 * 16];
++    read(0, val, sizeof(val) - 1);
++    setenv("TEST_VARIABLE", val, 1);
++
++  }
++
+   USE_VAR(argc);
+   USE_VAR(argv);
+   USE_VAR(env);