0xcpu/codeql-uboot

Step 5 - Using different classes and their predicates

github-learning-lab opened this issue · 2 comments

github-learning-lab commented

Step 5: Using different classes and their predicates

We want to identify integer values that are supplied from network data. A good way to spot those is to look for use of network ordering conversion macros such as ntohl, ntohll, and ntohs.

In the from section of the query, you declare some variables, and state the types of those variables. The type tells us what the possible values are for the variable.

In the previous query you were querying for values in the class Function to find functions in the source code. We have to query a different type to find macros in the source code instead. Can you guess its name?

NOTE: These Network ordering conversion utilities can be macros or functions depending on the platform. In this course, we are looking at a Linux database, where they are macros.

github-learning-lab commented

⌨️ Activity: Find all ntoh* macros

  1. Edit the file 5_macro_definitions.ql
  2. Write a query that finds the definitions of the macros named ntohs, ntohl or ntohll. Use the auto-completion in the Visual Studio Code extension to guide you:
    • Wait a moment after typing from to get a list of available classes in the CodeQL standard library for C/C++. Which class in this list represents macros? Create a variable with this class as its type.
    • In the where section, type <your_variable_name> followed by a dot ., and wait a moment to get the list of predicates available for a value in the variable's type. Hover over each predicate to see the inline documentation.
    • Which predicate will give us the name of a macro?
    • Use the or keyword to combine multiple conditions where you want at least one condition to be met. Here we are interested in three possible macro names.
  3. You can use a regular expression to write a more compact query that searches for all three macros at once, instead of using three cases combined by or. Check out the predicate string::regexpMatch in the built-in predicates for string. CodeQL uses the java.util.Pattern regexp conventions).
  4. Once you're happy with the results, submit your solution.
github-learning-lab commented

Congratulations, looks like the query you introduced in 175efd2 finds the correct results!

If you created a pull request, merge it.

Let's continue to the next step.