On 12/3/2013 1:44 AM, Peter Levart wrote:
On 12/03/2013 09:51 AM, Peter Levart wrote:
Hi,
While browsing the code of java.util.logging.Handler, I noticed a
theoretical possibility that a security check in a
j.u.l.StreamHandler be circumvented using a data race.
There is a plain boolean instance field 'sealed' in j.u.l.Handler
that is pre-initialized to 'true' in field initializer. StreamHandler
sublcass' constructors overwrite this value with 'false' at the
beginning, then issue some operations which circumvent security
checks, and finally they reset the 'sealed' value back to 'true' at
the end.
If a reference to an instance of StreamHandler or subclass is passed
to some thread without synchronization via data-race, this thread can
see 'true' or 'false' as the possible values of 'sealed' variable,
thus it is possible to circumvent security checks.
One possibility to fix this is moving the field to StreamHandler and
making it final:
http://cr.openjdk.java.net/~plevart/jdk8-tl/jul.Handler.sealed/webrev.01/
Just making the field volatile might not work. There is an ongoing
debate on concurrency-interest which suggests that volatile fields
are not exceptional in constructors like final fields are...
Regards, Peter
The proposed patch is not complete. There are several subclasses of
StreamHandler in the java.util.logging package that also need a way to
bypass security checks for some operations in their constructors. So
here's the updated webrev which updates them with the same code as
StreamHandler. This means that there are two copies of 'sealed' flag
in object of type ConsoleHandler, for example, but only the one
declared in ConsoleHandler is relevant for governing access checks:
http://cr.openjdk.java.net/~plevart/jdk8-tl/jul.Handler.sealed/webrev.02/
Before filing the bug, I'm asking the list whether this can be
considered a bug...
This does look a possible data race that might return a partially
constructed object with sealed = false. I am not sure how likely we
will run into this race though.
W.r.t. the patch, it might be better to get rid of the sealed field and
wrap the calls with doPrivileged with limited privilege (just
LoggingPermission("control"))
Mandy
