Re: use-after-free in sctp_do_sm

[Dmitry Vyukov <dvyukov@google.com>]

On Thu, Dec 3, 2015 at 9:51 PM, Joe Perches <joe@perches.com> wrote:
> (adding lkml as this is likely better discussed there)
>
> On Thu, 2015-12-03 at 15:42 -0500, Jason Baron wrote:
>> On 12/03/2015 03:24 PM, Joe Perches wrote:
>> > On Thu, 2015-12-03 at 15:10 -0500, Jason Baron wrote:
>> > > On 12/03/2015 03:03 PM, Joe Perches wrote:
>> > > > On Thu, 2015-12-03 at 14:32 -0500, Jason Baron wrote:
>> > > > > On 12/03/2015 01:52 PM, Aaron Conole wrote:
>> > > > > > I think that as a minimum, the following patch should be evaluted,
>> > > > > > but am unsure to whom I should submit it (after I test):
>> > > > []
>> > > > > Agreed - the intention here is certainly to have no side effects. It
>> > > > > looks like 'no_printk()' is used in quite a few other places that would
>> > > > > benefit from this change. So we probably want a generic
>> > > > > 'really_no_printk()' macro.
>> > > >
>> > > > https://lkml.org/lkml/2012/6/17/231
>> > >
>> > > I don't see this in the tree.
>> >
>> > It never got applied.
>> >
>> > > Also maybe we should just convert
>> > > no_printk() to do what your 'eliminated_printk()'.
>> >
>> > Some of them at least.
>> >
>> > > So we can convert all users with this change?
>> >
>> > I don't think so, I think there are some
>> > function evaluation/side effects that are
>> > required.  I believe some do hardware I/O.
>> >
>> > It'd be good to at least isolate them.
>> >
>> > I'm not sure how to find them via some
>> > automated tool/mechanism though.
>> >
>> > I asked Julia Lawall about it once in this
>> > thread:  https://lkml.org/lkml/2014/12/3/696
>> >
>>
>> Seems rather fragile to have side effects that we rely
>> upon hidden in a printk().
>
> Yup.
>
>> Just convert them and see what breaks :)
>
> I appreciate your optimism.  It's very 1995.
> Try it and see what happens.


But Aaron says that DYNAMIC_DEBUG is enabled in most major
distributions, and all these side-effects don't happen with
DYNAMIC_DEBUG. This suggests that we can make these side-effects not
happen without DYNAMIC_DEBUG as well.
Or I am missing something here?