On Fri, Feb 28, 2020 at 1:14 AM Paul Moore [off-list ref] wrote:

On Thu, Feb 27, 2020 at 10:40 AM Dmitry Vyukov [off-list ref] wrote:

quoted

On Mon, Feb 24, 2020 at 11:47 PM Paul Moore [off-list ref] wrote:

quoted

On Mon, Feb 24, 2020 at 5:43 PM Eric Paris [off-list ref] wrote:

quoted

https://syzkaller.appspot.com/x/repro.syz?x=151b1109e00000 (the
reproducer listed) looks like it is literally fuzzing the AUDIT_SET.
Which seems like this is working as designed if it is setting the
failure mode to 2.

So it is, good catch :)  I saw the panic and instinctively chalked
that up to a mistaken config, not expecting that it was what was being
tested.

Yes, this audit failure mode is quite unpleasant for fuzzing. And
since this is not a top-level syscall argument value, it's effectively
impossible to filter out in the fuzzer. Maybe another use case for the
"fuzer lockdown" feature +Tetsuo proposed.
With the current state of the things, I think we only have an option
to disable fuzzing of audit. Which is pity because it has found 5 or
so real bugs in audit too.
But this happened anyway because audit is only reachable from init pid
namespace and syzkaller always unshares pid namespace for sandboxing
reasons, that was removed accidentally and that's how it managed to
find the bugs. But the unshare is restored now:
https://github.com/google/syzkaller/commit/5e0e1d1450d7c3497338082fc28912fdd7f93a3c

As a side effect all other real bugs in audit will be auto-obsoleted
in future if not fixed because they will stop happening.

On the plus side, I did submit fixes for the other real audit bugs
that syzbot found recently and Linus pulled them into the tree today
so at least we have that small victory.

+1!

We could consider adding a fuzz-friendly build time config which would
disable the panic failsafe, but it probably isn't worth it at the
moment considering the syzbot's pid namespace limitations.

--
paul moore
www.paul-moore.com