...
Threads
...
always
...
preserve
...
class
...
invariants
...
when
...
they
...
are
...
allowed
...
to
...
exit
...
normally
...
.
...
Programmers
...
often
...
try
...
to
...
abruptly terminate
...
threads
...
when
...
they
...
believe
...
that
...
the
...
task
...
is
...
accomplished,
...
the
...
request
...
has
...
been
...
canceled
...
, or
...
the
...
program
...
or
...
JVM
...
needs
...
to
...
quickly
...
shut
...
down.
...
A
...
few
...
thread
...
APIs
...
were
...
introduced
...
to
...
facilitate
...
thread
...
suspension,
...
resumption
...
, and
...
termination
...
but
...
were
...
later
...
deprecated
...
because
...
of
...
inherent
...
design
...
weaknesses.
...
The
...
Thread.stop()
...
method
...
is
...
one
...
example.
...
It
...
causes
...
the
...
thread
...
to
...
immediately
...
throw
...
a
...
ThreadDeath
...
exception,
...
which
...
usually
...
stops
...
the
...
thread.
...
| Wiki Markup |
|---|
Invoking {{Thread.stop()}} results in the release of all the locks a thread has acquired which may corrupt the state of the object. The thread could catch the {{ThreadDeath}} exception and use a {{finally}} block in an attempt to repair the inconsistent object, however, this requires careful inspection of all the synchronized methods and blocks because a {{ThreadDeath}} exception can be thrown at any point during the thread's execution. Furthermore, code must be protected from {{ThreadDeath}} exceptions that may result when executing |
...
{{catch}} or {{finally}} blocks \[[Sun 99|AA. Java References#Sun 99]\]. |
...
More
...
information
...
about
...
deprecated
...
methods
...
is
...
available
...
in
...
...
...
...
...
...
...
...
...
.
...
Also,
...
refer
...
to
...
...
...
...
...
...
...
...
...
...
for
...
information
...
on
...
preventing
...
data
...
corruption
...
when
...
the
...
JVM
...
is
...
abruptly
...
shut
...
down.
...
Noncompliant Code Example (Deprecated Thread.stop()
...
)
...
This
...
noncompliant
...
code
...
example
...
shows
...
a
...
thread
...
that
...
fills
...
a
...
vector
...
with
...
pseudorandom
...
numbers.
...
The
...
thread
...
is
...
forcefully
...
stopped
...
after
...
a
...
given
...
amount
...
of
...
time.
| Code Block | ||||
|---|---|---|---|---|
| =
| |||
} public final class Container implements Runnable { private final Vector<Integer> vector = new Vector<Integer>(1000); public Vector<Integer> getVector() { return vector; } public synchronized void run() { Random number = new Random(123L); int i = vector.capacity(); while (i > 0) { vector.add(number.nextInt(100)); i--; } } public static void main(String[] args) throws InterruptedException { Thread thread = new Thread(new Container()); thread.start(); Thread.sleep(5000); thread.stop(); } } {code} |
Because
...
the
...
class
...
Vector
...
is
...
thread-safe,
...
operations
...
performed
...
by
...
multiple
...
threads
...
on
...
its
...
shared
...
instance
...
are
...
expected
...
to
...
leave
...
it
...
in
...
a
...
consistent
...
state.
...
For
...
instance,
...
the
...
Vector.size()
...
method
...
always
...
returns
...
the
...
correct
...
number
...
of
...
elements
...
in
...
the
...
vector
...
even
...
in
...
the
...
face
...
of
...
concurrent
...
changes
...
to
...
the
...
vector.
...
This
...
is
...
because
...
the
...
vector
...
instance
...
uses
...
its
...
own
...
intrinsic
...
lock
...
to
...
prevent
...
other
...
threads
...
from
...
accessing
...
it
...
while
...
its
...
state
...
is
...
temporarily
...
inconsistent.
...
| Wiki Markup |
|---|
However, the {{Thread.stop()}} method causes the thread to stop what it is doing and throw a {{ThreadDeath}} exception. All acquired locks are subsequently released \[[API 06|AA. Java References#API 06]\]. If the thread is in the process of adding a new integer to the vector when it is stopped, the vector may become accessible while it is in an inconsistent state. This can |
...
result |
...
in {{Vector.size()}} |
...
returning |
...
an |
...
incorrect |
...
element |
...
count, |
...
for |
...
example, because the element count is incremented after adding the element. |
Compliant Solution (volatile flag)
This compliant solution uses a volatile flag to terminate the thread. An accessor method shutdown() is used to set the flag to true. The thread's run() method polls the done flag, and terminates when it becomes true.
| Code Block | ||
|---|---|---|
| ||
). h2. Compliant Solution ({{volatile}} flag) This compliant solution uses a {{volatile}} flag to stop the thread. An accessor method {{shutdown()}} is used to set the flag to {{true}}. The thread's {{run()}} method polls the {{done}} flag, and terminates when it becomes {{true}}. {code:bgColor=#ccccff} public final class Container implements Runnable { private final Vector<Integer> vector = new Vector<Integer>(1000); private volatile boolean done = false; public Vector<Integer> getVector() { return vector; } public void shutdown() { done = true; } public synchronized void run() { Random number = new Random(123L); int i = vector.capacity(); while (!done && i > 0) { vector.add(number.nextInt(100)); i--; } } public static void main(String[] args) throws InterruptedException { Container container = new Container(); Thread thread = new Thread(container); thread.start(); Thread.sleep(5000); container.shutdown(); } } {code} h2. Compliant Solution |
Compliant Solution (Interruptible)
In this compliant solution, Thread.interrupt() is called from main() to terminate the thread. Invoking Thread.interrupt() sets an internal flag known as the interrupt status. The thread polls the interrupt status flag using the Thread.interrupted() method which returns true if the current thread has been interrupted and clears the interrupt status.
| Code Block | ||
|---|---|---|
| ||
This compliant solution stops the thread using the {{Thread.interrupt()}} method. {code:bgColor=#ccccff} public class Container implements Runnable { private final Vector<Integer> vector = new Vector<Integer>(1000); public Vector<Integer> getVector() { return vector; } public synchronized void run() { Random number = new Random(123L); int i = vector.capacity(); while (!Thread.interrupted() && i > 0) { vector.add(number.nextInt(100)); i--; } } public static void main(String[] args) throws InterruptedException { Container c = new Container(); Thread thread = new Thread(c); thread.start(); Thread.sleep(5000); thread.interrupt(); } } {code} This method interrupts the current thread, however, it only stops the thread because the code polls the interrupted flag using the method {{Thread.interrupted()}}. Upon receiving the interruption, the interrupted status of the thread is cleared and an {{InterruptedException}} is thrown. No guarantees are provided by the JVM on when the interruption will be detected by blocking methods such as {{Thread.sleep()}} and {{Object.wait()}}. A thread may use interruption for performing tasks other than cancellation and shutdown. Consequently, a thread should not be interrupted unless its [interruption policy|BB. Definitions#interruption policy] is known in advance. Failure to follow this advice can result in failed interruption requests {mc} I don't think this is true ~DS -> the corruption of mutable shared state. {mc} h2. Compliant Solution ({{RuntimePermission stopThread}}) Remove the default permission {{java.lang.RuntimePermission}} {{stopThread}} from the security policy file to deny the {{Thread.stop()}} invoking code, the required privileges. h2. Risk Assessment Forcing a thread to stop can result in inconsistent object state. Critical resources may also leak if clean-up operations are not carried out as required. || Rule || Severity || Likelihood || Remediation Cost || Priority || Level || | CON13- J | low | probable | medium | {color:green}{*}P4{*}{color} | {color:green}{*}L3{*}{color} | h3. Automated Detection TODO h3. Related Vulnerabilities Search for vulnerabilities resulting from the violation of this rule on the [CERT website|https://www.kb.cert.org/vulnotes/bymetric?searchview&query=FIELD+KEYWORDS+contains+CON35-J]. h2. References |
A thread may use interruption for performing tasks other than cancellation and shutdown. Consequently, a thread should not be interrupted unless its interruption policy is known in advance. Failure to follow this advice can result in failed interruption requests.
Compliant Solution (RuntimePermission stopThread)
Remove the default permission java.lang.RuntimePermission stopThread from the security policy file to deny the Thread.stop() invoking code, the required privileges.
Risk Assessment
Forcing a thread to stop can result in inconsistent object state. Critical resources may also leak if clean-up operations are not carried out as required.
Rule | Severity | Likelihood | Remediation Cost | Priority | Level |
|---|---|---|---|---|---|
CON13- J | low | probable | medium | P4 | L3 |
Automated Detection
TODO
Related Vulnerabilities
Search for vulnerabilities resulting from the violation of this rule on the CERT website.
References
| Wiki Markup |
|---|
\[[API 06|AA. Java References#API 06]\] Class Thread, method {{stop}}, interface ExecutorService
\[[Sun 99|AA. Java References#Sun 99]\]
\[[Darwin 04|AA. Java References#Darwin 04]\] 24.3 Stopping a Thread
\[[JDK7 08|AA. Java References#JDK7 08]\] Concurrency Utilities, More information: Java Thread Primitive Deprecation
\[[JPL 06|AA. Java References#JPL 06]\] 14.12.1. Don't stop and 23.3.3. Shutdown Strategies
\[[JavaThreads 04|AA. Java References#JavaThreads 04]\] 2.4 Two Approaches to Stopping a Thread
\[[Goetz 06|AA. Java References#Goetz 06]\] Chapter 7: Cancellation and shutdown |
...
...
...
...
...
...
...
...
...
...
...
...
...
order 11. Concurrency (CON) CON15-J.
...
...
...
...
...
...
...
...
...
...