[Bug libgcj/23367] New: _Jv_FindMethodInCache is not thread-safe

["greenrd at greenrd dot org" <gcc-bugzilla at gcc dot gnu dot org>]

_Jv_FindMethodInCache is not thread-safe, because it assumes that the following
check is enough to assure thread-safety:

 _Jv_mcache *mc = method_cache + index;
 _Jv_Method *m = mc->method;

  if (mc->klass == klass
      && m != NULL             // thread safe check
      && _Jv_equalUtf8Consts (m->name, name)
      && _Jv_equalUtf8Consts (m->signature, signature))

But this is bogus! If mc has already been assigned to, m will not be null, but
if it has never been assigned to, m will be null, so it's a useless check.
Therefore there is no effective measure for thread safety, so it's not thread-safe.

This could cause fairly arbitrary bad behaviour, including NPEs, security
violations, and weird hard-to-reproduce bugs.

I believe I have seen an NPE caused by this bug, because the symptoms match what
would be expected from this bug, and I know of no other plausible cause for
these symptoms: Method called with "this" object being of incompatible type, so
the method tries to read the "this" object as if it were the expected class, and
receives garbage (in this case, 0x0).

-- 
           Summary: _Jv_FindMethodInCache is not thread-safe
           Product: gcc
           Version: 4.0.2
            Status: UNCONFIRMED
          Severity: critical
          Priority: P2
         Component: libgcj
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: greenrd at greenrd dot org
                CC: gcc-bugs at gcc dot gnu dot org,java-prs at gcc dot gnu
                    dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23367