Step 5 - Using different classes and their predicates

[github-learning-lab[bot]]

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[bot]]

:keyboard: 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. To write a more compact query that searches for all three macros at once, instead of using three cases combined by or you have 2 choices:
   • Use a regular expression. Check out the predicate string::regexpMatch in the built-in predicates for string. CodeQL uses the java.util.Pattern regexp conventions).
   • Use a set literal expression to equate <your_variable_name> to a lists of choices <your_variable_name> in ['bar', 'baz', 'quux']
4. Once you're happy with the results, submit your solution.

[github-learning-lab[bot]]

Ooops! The query you submitted in 432038d622f9c20d981d01294e80c16e71493fcb didn't find the right results. Please take a look at the comment and try again.

To submit a new iteration of your query, you just have to push a new commit to the same branch (main or the PR branch).

[github-learning-lab[bot]]

Ooops! The query you submitted in 449bb18412aa66f4c38f35f0329a3e1411e5f61d didn't find the right results. Please take a look at the comment and try again.

To submit a new iteration of your query, you just have to push a new commit to the same branch (main or the PR branch).

[github-learning-lab[bot]]

Congratulations, looks like the query you introduced in 55a76228e56abdbfad757844ebfdf83583af6723 finds the correct results!

If you created a pull request, merge it.

Let's continue to the next step.