On 07/23/2014 07:07 AM, Tom Hawtin wrote:
On 23/07/2014 05:26, David M. Lloyd wrote:
I would suggest that one or more of the following be done to mitigate
this problem:
• Always have static initialization blocks be privileged (this does
require users to be cognizant of this fact when writing static blocks)
If we were following "secure by default", this would break it. It turns
out having a static initaliser run with an unprivileged acc highlights
code that is doing something naughty.
I thought this mindset might dominate, which is unfortunate. In
practice, it is far better for code to be predictable, concise, and
clear. It does not really make any sense to have random security
contexts in place and then call it "secure"; it makes more sense to just
tell people "hey your static initializers are privileged". It's not
like normal directly invokable methods where the user can pass in
arguments and get return values from code that runs in a privileged
context. It is very, very unusual for a static initializer to perform
any function which is practically exploitable; they are generally
stateless already, taking no input and producing no output. I don't
think that it can be shown that the blanket ideology really provides any
measurable, real-world benefit; on the contrary, it causes real,
measurable detriment. I don't think anyone ever said "Oh, it's a good
thing I got that AccessControlException in my static initializer; now I
know that doing XYZ needed a privileged block".
Nevertheless, I never actually expected to convince anyone of this -
it's one of those ideas which seems culturally "against the grain", i.e.
the general principle tends to outweigh the practical reality. Still, I
had to propose it, in order to be right with myself. :-)
• Allow static initialization blocks to partake in the aforementioned
annotation-driven privileged method idea
Together with the last point, this does make the elevated privilege
contain a wider block of code than is necessary. This is [particularly
the case with static initialisers and initialisers where the code can be
spread throughout the class. OTOH, relevant sections of code could be
split out into small methods.
Exactly - in this case I would even expect that you could separately
annotate each static init with its privileges. The important thing
would still be that the compiler can do this without constructing a new
class for each chunk (or even a lambda if it could be avoided).
• Introduce a new permission checking mechanism which examines only a
specific relevant caller's protection domain (perhaps determined by
filter expression, possibly using the stack examination scheme that
Mandy Chung has been working on)
Immediate caller checking, though has similarities to link-time access
checking, has a spectacularly unfortunate history.
That is an observation. :-)
• Introduce a programmatic "elevation" mechanism that increases the
privileges of the currently executing method for the remainder of its
execution without requiring a call-in to doPrivileged or instantiation
of a privileged action object
Tom
--
- DML
