On Mon, Oct 10, 2016 at 04:03:39PM +0200, Julien Charbon wrote:
>
> Hi Slawa,
>
> On 10/10/16 3:32 PM, Slawa Olhovchenkov wrote:
> > On Mon, Oct 10, 2016 at 01:26:12PM +0200, Julien Charbon wrote:
> >> On 10/6/16 1:10 PM, Slawa Olhovchenkov wrote:
> >>> On Thu, Oct 06, 2016 at 09:28:06AM +0200, Julien Charbon
wrote:
> >>>
> >>>> 2. thread1: In tcp_close() the inp is marked with
INP_DROPPED flag, the
> >>>> process continues and calls INP_WUNLOCK() here:
> >>>>
> >>>>
https://github.com/freebsd/freebsd/blob/releng/11.0/sys/netinet/tcp_subr.c#L1568
> >>>
> >>> Look also to sys/netinet/tcp_timewait.c:488
> >>>
> >>> And check other locks from r160549
> >>
> >> You are right, and here the a fix proposal for this issue:
> >>
> >> Fix a double-free when an inp transitions to INP_TIMEWAIT state
after
> >> having been dropped
> >> https://reviews.freebsd.org/D8211
> >>
> >> It basically enforces in_pcbdrop() logic in tcp_input(): A
INP_DROPPED
> >> inpcb should never be proceed further.
> >>
> >> Slawa, as you are the only one to reproduce this issue currently,
could
> >> test this patch? (And remove the temporary patch I did provided
to you
> >> before).
> >>
> >> I will wait for your tests results before pushing further.
> >>
> >> Thanks!
> >>
> >> diff --git a/sys/netinet/tcp_input.c b/sys/netinet/tcp_input.c
> >> index c72f01f..37f27e0 100644
> >> --- a/sys/netinet/tcp_input.c
> >> +++ b/sys/netinet/tcp_input.c
> >> @@ -921,6 +921,16 @@ findpcb:
> >> goto dropwithreset;
> >> }
> >> INP_WLOCK_ASSERT(inp);
> >> + /*
> >> + * While waiting for inp lock during the lookup, another
thread
> >> + * can have droppedt the inpcb, in which case we need to
loop back
> >> + * and try to find a new inpcb to deliver to.
> >> + */
> >> + if (inp->inp_flags & INP_DROPPED) {
> >> + INP_WUNLOCK(inp);
> >> + inp = NULL;
> >> + goto findpcb;
> >
> > Are you sure about this goto?
> > Can this cause infinite loop by found same inpcb?
> > May be drop packet is more correct?
>
> Good question: Infinite loop is not possible here, as the next TCP
> hash lookup will return NULL or a fresh new and not dropped inp. You
I am not expert in this api and don't see cause of this: I am assume
hash lookup don't remove from hash returned args and I am don't see
any removing of this inp. Why hash lookup don't return same inp?
(assume this input patch interrupt callout code on the same CPU core).
> can check the current other usages of goto findpcb in tcp_input(). The
> rational here being:
>
> - Behavior before the patch: If the inp we found was deleted then goto
> findpcb.
> - Behavior after the patch: If the inp we found was deleted or dropped
> then goto findpcb.
>
> I just prefer having the same behavior applied everywhere: If
> tcp_input() loses the inp lock race and the inp was deleted or dropped
> then retry to find a new inpcb to deliver to.
>
> But you are right dropping the packet here will also fix the issue.
>
> Then the review process becomes quite helpful because people can argue:
> Dropping here is better because "blah", or goto findpcb is
better
> because "bluh", etc. And at the review end you have a nice final
patch.
>
> https://reviews.freebsd.org/D8211
I am not sure, I am see to
sys/netinet/in_pcb.h:#define INP_DROPPED 0x04000000 /* protocol
drop flag */
and think this is a flag 'all packets must be droped'