rspec/rules/S2259/java/rule.adoc

== Why is this an issue?

A reference to ``++null++`` should never be dereferenced/accessed. Doing so will cause a ``++NullPointerException++`` to be thrown. At best, such an exception will cause abrupt program termination. At worst, it could expose debugging information that would be useful to an attacker, or it could allow an attacker to bypass security measures.


Note that when they are present, this rule takes advantage of ``++@CheckForNull++`` and ``++@Nonnull++`` annotations defined in https://jcp.org/en/jsr/detail?id=305[JSR-305] to understand which values are and are not nullable except when ``++@Nonnull++`` is used on the parameter to ``++equals++``, which by contract should always work with null.

=== Noncompliant code example

[source,java]
----
@CheckForNull
String getName(){...}

public boolean isNameEmpty() {
  return getName().length() == 0; // Noncompliant; the result of getName() could be null, but isn't null-checked
}
----

[source,java]
----
Connection conn = null;
Statement stmt = null;
try{
  conn = DriverManager.getConnection(DB_URL,USER,PASS);
  stmt = conn.createStatement();
  // ...

}catch(Exception e){
  e.printStackTrace();
}finally{
  stmt.close();   // Noncompliant; stmt could be null if an exception was thrown in the try{} block
  conn.close();  // Noncompliant; conn could be null if an exception was thrown 
}
----

[source,java]
----
private void merge(@Nonnull Color firstColor, @Nonnull Color secondColor){...}

public  void append(@CheckForNull Color color) {
    merge(currentColor, color);  // Noncompliant; color should be null-checked because merge(...) doesn't accept nullable parameters
}
----

[source,java]
----
void paint(Color color) {
  if(color == null) {
    System.out.println("Unable to apply color " + color.toString());  // Noncompliant; NullPointerException will be thrown
    return;
  }
  ...
}
----

== Resources

* https://cwe.mitre.org/data/definitions/476[MITRE, CWE-476] - NULL Pointer Dereference
* https://wiki.sei.cmu.edu/confluence/x/QdcxBQ[CERT, EXP34-C.] - Do not dereference null pointers
* https://wiki.sei.cmu.edu/confluence/x/aDdGBQ[CERT, EXP01-J.] - Do not use a null in a case where an object is required

ifdef::env-github,rspecator-view[]

'''
== Implementation Specification
(visible only on this page)

=== Message

* 'XXXX' is nullable here and method 'YYY' don't accept nullable argument
* NullPointerException might be thrown as 'XXXX' is nullable here


include::../highlighting.adoc[]

'''
== Comments And Links
(visible only on this page)

=== on 23 Mar 2015, 13:15:46 Freddy Mallet wrote:
@Ann, could you review this sub-task ? Thanks

=== on 24 Mar 2015, 12:47:38 Samuel Mercier wrote:
first example is wrong, since ``++instanceof++`` would return ``++false++`` if ``++obj++`` is ``++null++``.

Interestingly, from null/notnull point of view, ``++a instanceof b++`` is equivalent to ``++a != null++``

=== on 24 Mar 2015, 13:45:55 Samuel Mercier wrote:
\[~ann.campbell.2] I updated the first non compliant code snippet.

=== on 24 Mar 2015, 15:02:13 Samuel Mercier wrote:
Removed message * NullPointerException will be thrown as 'XXXX' is for sure null here, since we are currently unable to make distinction between @Nullable and if (... == null)

=== on 19 Sep 2019, 05:14:31 QXO wrote:
This code shouldnot should not be a issue ( in `url.substring(0,start)` url never not null)

It's sonarqube(7.9.1) check implements issue, please fix the issue:)

----
public String testSonarNullCheckIssue(final String url,final boolean isUrl) { 
   int start = url != null && isUrl ? url.indexOf('?') : -1;
   if(start != -1 ){ 
       return url.substring(0,start);
   }
   return url;
} {code}

ref: https://drive.google.com/open?id=1MuZMBm8bkwz_Q5mZIwEaDsJoh-qaopW_
----

=== on 19 Sep 2019, 07:24:31 Alexandre Gigleux wrote:
Thanks for the feedback [~qxo]!

Can you report the FP in the community forum \https://community.sonarsource.com/tags/c/bug/fp/java so it gets more visibility and be addressed?

JIRA comments are not convenient to manage FPs.

Thanks

include::../comments-and-links.adoc[]

endif::env-github,rspecator-view[]