Re: general protection fault in in_aton

[Dmitry Vyukov]

On Tue, Jul 10, 2018 at 10:15 PM, Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> On Tue, Jul 10, 2018 at 12:57 PM Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote:
>>
>> Is it really hard to get fault address? I know that userspace
>> generally receives fault address in siginfo.
>
> For an actual page fault it's trivial.
>
> However, for invalid addresses (aka "non-canonical"), you don't even
> get a page fault, you get a GP like in this case. And then the actual
> address is not available.


I see. Then I don't have any great ideas. Running without KASAN would
result in more, much more cryptic crashes.

FWIW for these "GPF could be caused by NULL-ptr deref" I first just
assume that it's in fact a NULL deref. And in this case it all pretty
quickly forms a consistent picture that it's indeed just a missing a
NULL pointer check. That dffffc0000000000 in a register also a good
hint.