External programs can be invoked from Java code using the exec() method of java.lang.Runtime class. As a result, a reference to the Process class is returned to the JVM. The exitValue() method can be used to observe the return value of the process. There are several nuances of Rutime.exec() that are discussed below.
...
Noncompliant Code Example
This non-compliant noncompliant code example calls notemaker, a hypothetical cross-platform notepad application. Despite compiling successfully, it throws an IllegalThreadStateException if the notemaker process has not completed.
...
By using the waitFor() method for blocking, this code can be modified as shown in the modified non-compliant noncompliant example below. This also has a shortcoming: the program hangs due to the limited buffer size used for standard output streams on many platforms. This is the result of failure in reading/writing to the streams in a timely fashion.
| Code Block | ||
|---|---|---|
| ||
public class exec {
public static void main(String args[]) {
try {
Runtime rt = Runtime.getRuntime();
Process proc = rt.exec("notemaker");
int exitVal = proc.waitFor();
} catch (Throwable t) { t.printStackTrace();}
}
}
|
Compliant Solution
An inefficient solution would be to exhaust the output (or stderr) stream before beginning to wait for the process. A better option is to empty both the stderr and output streams. The code below illustrates shows this but is not the best solution since it does not process any arguments passed to the external program (notemaker) and in turn exits with an OS-specific non-zero exit code.
...
| Code Block | ||
|---|---|---|
| ||
class exec extends Thread {
InputStream is;
String type;
OutputStream os;
exec(InputStream is, String type) {
this(is, type, null);
}
exec(InputStream is, String type, OutputStream redirect) {
this.is = is;
this.type = type;
this.os = redirect;
}
public void run() {
try {
PrintWriter pw = null;
if (os != null) {
pw = new PrintWriter(os);
}
InputStreamReader isr = new InputStreamReader(is);
BufferedReader br = new BufferedReader(isr);
String line=null;
while ( (line = br.readLine()) != null) {
if (pw != null) {
pw.println(line);
pw.flush();
}
System.out.println(type + ">" + line);
}
if (pw != null)
pw.flush();
} catch (IOException ioe) { ioe.printStackTrace(); }
}
}
public class execMe {
public static void main(String[] args)
{
// ... perform command argument check ...
try {
FileOutputStream fos = new FileOutputStream("c:\\output.txt");
Runtime rt = Runtime.getRuntime();
Process proc = rt.exec("notemaker");
// any error message?
exec errorGobbler = new exec(proc.getErrorStream(), "ERROR");
// any output?
exec outputGobbler = new exec(proc.getInputStream(), "OUTPUT", fos);
errorGobbler.start();
outputGobbler.start();
// any error?
int exitVal = proc.waitFor();
errorGobbler.join(); //handle condition where the
outputGobbler.join(); //process ends before the threads finish
fos.flush();
fos.close();
} catch (Throwable t) { t.printStackTrace(); }
}
}
|
Risk Assessment
TODO
Rule | Severity | Likelihood | Remediation Cost | Priority | Level |
|---|---|---|---|---|---|
FIO02-J | ?? | ?? | ?? | P?? | L?? |
Automated Detection
TODO
Related Vulnerabilities
Search for vulnerabilities resulting from the violation of this rule on the CERT website.
References
Javaworld article http://www.javaworld.com/javaworld/jw-12-2000/jw-1229-traps.html?
More Java Pitfalls, Pitfall 1
Sun Java Documentation