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topic reordering
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=Michael Hohn
=Michael Hohn
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@@ -3,12 +3,16 @@
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-->
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# CodeQL tutorial for C/C++: data flow and SQL injection
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xx:
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md_toc github < codeql-dataflow-sql-injection.md
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- [CodeQL tutorial for C/C++: data flow and SQL injection](#codeql-tutorial-for-cc-data-flow-and-sql-injection)
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- [Setup instructions](#setup-instructions)
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- [Documentation links](#documentation-links)
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- [The Problem in Action: running the code to see the problem](#the-problem-in-action-running-the-code-to-see-the-problem)
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- [Problem statement](#problem-statement)
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- [Tutorial, part 1: running the code to see the problem](#tutorial-part-1-running-the-code-to-see-the-problem)
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- [Data flow overview and illustration](#data-flow-overview-and-illustration)
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- [Tutorial, part 3: recap, sources and sinks](#tutorial-part-3-recap-sources-and-sinks)
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- [Tutorial: recap, sources and sinks](#tutorial-recap-sources-and-sinks)
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- [Codeql recap](#codeql-recap)
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- [Call to SQL query execution (the data sink)](#call-to-sql-query-execution-the-data-sink)
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- [Non-constant query strings and untrusted data (the data source)](#non-constant-query-strings-and-untrusted-data-the-data-source)
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@@ -16,7 +20,7 @@
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- [Taint flow configuration](#taint-flow-configuration)
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- [Path problem setup](#path-problem-setup)
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- [Path problem query format](#path-problem-query-format)
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- [Tutorial, part 2: data flow details](#tutorial-part-2-data-flow-details)
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- [Tutorial: data flow details](#tutorial-data-flow-details)
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- [isSource predicate ](#issource-predicate-)
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- [isSink predicate ](#issink-predicate-)
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- [Additional data flow features: the isAdditionalTaintStep predicate](#additional-data-flow-features-the-isadditionaltaintstep-predicate)
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@@ -54,6 +58,78 @@ If you get stuck, try searching our documentation and blog posts for help and id
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- [Learning CodeQL for C/C++](https://help.semmle.com/QL/learn-ql/cpp/ql-for-cpp.html)
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- [Using the CodeQL extension for VS Code](https://help.semmle.com/codeql/codeql-for-vscode.html)
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## The Problem in Action: running the code to see the problem
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This program can be compiled and linked, and a simple sqlite db created via
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```sh
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# Build
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./build.sh
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# Prepare db
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./admin rm-db
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./admin create-db
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./admin show-db
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```
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Users can be added via `stdin` in several ways; the second is a pretend "server"
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using the `echo` command.
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```sh
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# Add regular user interactively
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./add-user 2>> users.log
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First User
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# Regular user via "external" process
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echo "User Outside" | ./add-user 2>> users.log
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```
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Check the db and log:
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```
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# Check
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./admin show-db
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tail -4 users.log
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```
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Looks ok:
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```
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0:$ ./admin show-db
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87797|First User
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87808|User Outside
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0:$ tail -4 users.log
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[Tue Jul 21 14:15:46 2020] query: INSERT INTO users VALUES (87797, 'First User')
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[Tue Jul 21 14:17:07 2020] query: INSERT INTO users VALUES (87808, 'User Outside')
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```
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But there may be bad input; this one guesses the table name and drops it:
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```sh
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# Add Johnny Droptable
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./add-user 2>> users.log
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Johnny'); DROP TABLE users; --
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```
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And then we have this:
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```sh
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# And the problem:
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./admin show-db
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0:$ ./admin show-db
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Error: near line 2: no such table: users
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```
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What happened? The log shows that data was treated as command:
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```
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1:$ tail -4 users.log
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[Tue Jul 21 14:15:46 2020] query: INSERT INTO users VALUES (87797, 'First User')
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[Tue Jul 21 14:17:07 2020] query: INSERT INTO users VALUES (87808, 'User Outside')
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[Tue Jul 21 14:18:25 2020] query: INSERT INTO users VALUES (87817, 'Johnny'); DROP TABLE users; --')
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```
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Looking ahead, we now *know* that there is unsafe external data (source)
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which reaches (flow path) a database-writing command (sink). Thus, a query
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written against this code should find at least one taint flow path.
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## Problem statement
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Many security problems can be phrased in terms of _information flow_:
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@@ -70,9 +146,9 @@ data etc.
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We will use CodeQL to analyze the source code constructing a SQL
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query using string concatenation and then executing that query
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string. The following example uses the `sqlite3` library and
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- receives user-provided data from `stdin`,
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- uses environment data in `id`,
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string. The following example uses the `sqlite3` library; it
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- receives user-provided data from `stdin` and keeps it in `buf`
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- uses environment data and stores it in `id`,
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- runs a query in `sqlite3_exec`
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This is intentionally simple code, but it has all the elements that have to be
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@@ -150,8 +226,8 @@ int main(int argc, char* argv[]) {
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```
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In terms of sources, sinks, and information flow, the concrete problem is:
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1. specifying `stdin` as **source** using codeql,
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In terms of sources, sinks, and information flow, the concrete problem for codeql is:
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1. specifying `buf` as **source**,
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2. specifying the `query` argument to `sqlite3_exec()` as **sink**,
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3. specifying some code-specific data flow steps for the codeql library,
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3. using the codeql taint flow library find taint flow paths (if there are any)
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@@ -160,77 +236,7 @@ In terms of sources, sinks, and information flow, the concrete problem is:
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In the following, we go into more concrete detail and develop codedql scripts to
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solve this problem.
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## Tutorial, part 1: running the code to see the problem
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This program can be compiled and linked, and a simple sqlite db created via
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```sh
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# Build
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./build.sh
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# Prepare db
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./admin rm-db
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./admin create-db
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./admin show-db
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```
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Users can be added via `stdin` in several ways; the second is a pretend "server"
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using the `echo` command.
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```sh
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# Add regular user interactively
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./add-user 2>> users.log
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First User
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# Regular user via "external" process
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echo "User Outside" | ./add-user 2>> users.log
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```
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Check the db and log:
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```
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# Check
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./admin show-db
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tail -4 users.log
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```
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Looks ok:
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```
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0:$ ./admin show-db
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87797|First User
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87808|User Outside
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0:$ tail -4 users.log
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[Tue Jul 21 14:15:46 2020] query: INSERT INTO users VALUES (87797, 'First User')
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[Tue Jul 21 14:17:07 2020] query: INSERT INTO users VALUES (87808, 'User Outside')
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```
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But there may be bad input; this one guesses the table name and drops it:
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```sh
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# Add Johnny Droptable
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./add-user 2>> users.log
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Johnny'); DROP TABLE users; --
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```
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And then we have this:
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```sh
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# And the problem:
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./admin show-db
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0:$ ./admin show-db
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Error: near line 2: no such table: users
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```
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What happened? The log shows that data was treated as command:
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```
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1:$ tail -4 users.log
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[Tue Jul 21 14:15:46 2020] query: INSERT INTO users VALUES (87797, 'First User')
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[Tue Jul 21 14:17:07 2020] query: INSERT INTO users VALUES (87808, 'User Outside')
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[Tue Jul 21 14:18:25 2020] query: INSERT INTO users VALUES (87817, 'Johnny'); DROP TABLE users; --')
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```
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Looking ahead, we now *know* that there is unsafe external data (source)
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which reaches (flow path) a database-writing command (sink). Thus, a query
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written against this code should find at least one taint flow path.
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## Data flow overview and illustration
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In the previous sections we identified the sources of problematic strings
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@@ -271,7 +277,7 @@ nodes, rather than for the full graph.
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To illustrate the dataflow for this problem, we have a [collection of slides](https://drive.google.com/file/d/1eEG0eGVDVEQh0C-0_4UIMcD23AWwnGtV/view?usp=sharing)
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for this workshop.
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## Tutorial, part 3: recap, sources and sinks
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## Tutorial: recap, sources and sinks
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XX:
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<!--
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!-- The complete project can be downloaded via this
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||||
@@ -332,7 +338,7 @@ from FunctionCall fc
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where fc.<tab>
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```
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Now, we are looking for the call's `*target*`; completion shows `getTarget()`,
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Now, we are looking for the call's *target*; completion shows `getTarget()`,
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and we can finish that to
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```ql
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@@ -482,7 +488,7 @@ where
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select sink, source, sink, "Sqli flow from $@", source, "source"
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```
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## Tutorial, part 2: data flow details
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## Tutorial: data flow details
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With the dataflow configuration in place, we just need to provide the details for source(s), sink(s), and taint step(s).
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### isSource predicate
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