Hi, On 10/10/16 4:29 PM, Slawa Olhovchenkov wrote: > On Mon, Oct 10, 2016 at 04:03:39PM +0200, Julien Charbon wrote: >> 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'
On 10/10/16 4:29 PM, Slawa Olhovchenkov wrote: > On Mon, Oct 10, 2016 at 04:03:39PM +0200, Julien Charbon wrote: >> 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' Hm, I believe this flag means "this inp has been dropped by the TCP stack, so don't use it anymore". Actually this flag is better described in the function that sets it: "(INP_DROPPED) is used by TCP to mark an inpcb as unused and avoid future packet delivery or event notification when a socket remains open but TCP has closed." https://github.com/freebsd/freebsd/blob/release/11.0.0/sys/netinet/in_pcb.c#L1320 /* * in_pcbdrop() removes an inpcb from hashed lists, releasing its address and * port reservation, and preventing it from being returned by inpcb lookups. * * It is used by TCP to mark an inpcb as unused and avoid future packet * delivery or event notification when a socket remains open but TCP has * closed. This might occur as a result of a shutdown()-initiated TCP close * or a RST on the wire, and allows the port binding to be reused while still * maintaining the invariant that so_pcb always points to a valid inpcb until * in_pcbdetach(). * */ void in_pcbdrop(struct inpcb *inp) { inp->inp_flags |= INP_DROPPED; ... The classical example where "goto findpcb" is useful: You receive a new connection request with a TCP SYN packet and this packet is unlucky and reached a inp being dropped: - with "goto findpcb" approach, the next lookup will most likely find the LISTEN inp and start the TCP hand-shake as usual - with "drop the packet" approach, the TCP client will need to re-transmit a TCP SYN packet It is not because a packet was unlucky once that it deserves to be dropped. :) -- Julien
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