Re: Bugs involving maliciously crafted file system

[Dmitry Vyukov <dvyukov@google.com>]

On Sat, May 26, 2018 at 10:24 PM, Theodore Y. Ts'o <tytso@mit.edu> wrote:
> On Sat, May 26, 2018 at 07:12:49PM +0200, Dmitry Vyukov wrote:
>>
>> I don't see that "some kind of machine learning or expert system
>> evaluation" is feasible. At least not in short/mid-term. There are
>> innocently-looking bugs that actually turn out to be very bad, and
>> there are badly looking at first glance bugs that actually not that
>> bad for some complex reasons. Full security assessment is a complex
>> task and I think stays "human expert area" for now. One can get some
>> coarse estimation by searching for "use-after-free" and
>> "out-of-bounds" on the dashboard.
>
> If the kernel intentionally triggers a BUG_ON or a panic (as in file
> systems configured with 'tune2fs -e panic') it's pretty obvious that
> those errors can't be weaponized to execute code chosen by the
> attacker.  Would you agree with that?
>
> The same should be true for "blocked for more than 120 seconds";
> again, I claim that those sorts of errors are by definition less
> serious than buffer overruns.
>
> So there is at least some kind of automated evaluation that can be
> done, even if the general case problem is really hard.

These can't be weaponized to execute code, but if a BUG_ON is
triggerable over a network, or from VM guest, then it's likely more
critical than a local code execution. That's why I am saying that
automated evaluation is infeasible.

Anyway, bug type (UAF, BUG, task hung) is available in the bug title
on dashboard and on mailing lists, so you can just search/sort bugs on
the dashboard. What other interface you want on top of this?



>> > Or maybe it would be useful if there was a way where maintainers could
>> > be able to annotate bugs with priority and severity levels, and maybe
>> > make comments that can be viewed from the Syzbot dashboard UI.
>>
>> This looks more realistic. +Tetsuo proposed something similar:
>> https://github.com/google/syzkaller/issues/608
>>
>> I think to make it useful we need to settle on some small set of
>> well-defined tags for bugs that we can show on the dashboard.
>> Arbitrary detailed free-form comments can be left on the mailing list
>> threads that are always referenced from the dashboard.
>>
>> What tags would you use today for existing bugs? One would be
>> "security-critical", right?
>
> For me, it's not about tags.  Things missing from the
> https://syzkaller.appspot.com/ front page are:
>
> * Whether or not a repro is available

This was always available in the Repro column.

> * Which subsystems the bug has been tentatively assigned
> * A maintainer assigned priority and severity level

Let's call this tags collectively (unless you have a better name). P0
or subsystem:ext4 can also be tags.
So  you mean: (1) priority levels (P0, P1, P2), (2) severity levels
(S0, S1, S2) and subsystem, right?

On a related note, perhaps kernel community needs to finally start
using bugzilla for real, like with priorities, assignees, up-to-date
statuses, no stale bugs, etc. All of this is available in bug tracking
systems for decades...