Documentation Source Text

<tcl>hd_fragment aflfuzz {American Fuzzy Lop fuzzer}</tcl>
<h4>4.1.1 SQL Fuzz Using The American Fuzzy Lop Fuzzer</h4>

<p>The <a href="http://lcamtuf.coredump.cx/afl/">American Fuzzy Lop</a>
or "AFL" fuzzer is a recent (circa 2014) innovation from Michal Zalewski.
Unlike most other fuzzers that blindly generate random inputs, the AFL
fuzzer instruments the program being tested (by modifying the assembly-language
output from the C compiler) and uses that instrumentation to detect when
an input causes the program to do something different - to follow
a new control path or loop a different number of times.  Inputs that provoke
new behavior are retained and further mutated.  In this way, AFL is able
to "discover" new behaviors of the program under test, including behaviors
that were never envisioned by the designers.

<p>AFL has proven remarkably adept at finding arcane bugs in SQLite.
Most of the findings have been assert() statements where the conditional
was false under obscure circumstances.  But AFL has also found
a fair number of crash bugs in SQLite, and even a few cases where SQLite 
computed incorrect results.

<p>Because of its past success, AFL became a standard part of the testing
strategy for SQLite beginning with [version 3.8.10].  There are at least two
instance of AFL running against SQLite continuously, 24/7/365, trying new
randomly mutated inputs against SQLite at a rate of a few hundred to a few
thousand per second.  Both SQL statements and database files are fuzzed.
Billions and billions of mutations have been tried, but AFL's 
instrumentation has narrowed them down to less than 30,000 test cases that
cover all distinct behaviors.  Newly discovered test cases are periodically
captured and added to the [TCL test suite] where they can be rerun using
the "make fuzztest" command.

<h3>4.2 Malformed Database Files</h3>

<p>There are numerous test cases that verify that SQLite is able to
deal with malformed database files.
These tests first build a well-formed database file, then add
corruption by changing one or more bytes in the file by some means