Date: Wed, 17 Jul 2019 20:23:26 +0200 From: Michael Tuexen <tuexen@freebsd.org> To: Vitalij Satanivskij <satan@ukr.net> Cc: freebsd-net@freebsd.org, Paul <devgs@ukr.net> Subject: Re: Issues with TCP Timestamps allocation Message-ID: <B7BD397D-1B0E-4EFD-94EE-483C22952CD7@freebsd.org> In-Reply-To: <20190717074243.GA65665@hell.ukr.net> References: <1562579483.67527000.24rw4xi5@frv39.fwdcdn.com> <32FD061B-245C-41D2-81DE-1B4756A7173D@freebsd.org> <1562591379.369129000.gpmxvurq@frv39.fwdcdn.com> <DF65CA7F-B5FC-499D-B053-0531596D230C@freebsd.org> <1562599181.734953000.1l9a1d23@frv39.fwdcdn.com> <0C475A01-9BCD-4E4A-9731-09AB919CA9BE@freebsd.org> <1562676414.933145000.z3zteyqp@frv39.fwdcdn.com> <1E9F3F99-C3E9-44DD-AA70-9B11E19D4769@freebsd.org> <20190717074243.GA65665@hell.ukr.net>
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> On 17. Jul 2019, at 09:42, Vitalij Satanivskij <satan@ukr.net> wrote: >=20 >=20 >=20 > Hello.=20 >=20 > Is there any changes about this problem Please find a patch in https://reviews.freebsd.org/D20980 If possible, please test and report. Best regards Michael >=20 >=20 > I'm using FreeBSD 12 on my desktop and can confirm problem occur with = some hosts. >=20 >=20 >=20 > Michael Tuexen wrote: > MT>=20 > MT>=20 > MT> > On 9. Jul 2019, at 14:58, Paul <devgs@ukr.net> wrote: > MT> >=20 > MT> > Hi Michael, > MT> >=20 > MT> > 9 July 2019, 15:34:29, by "Michael Tuexen" <tuexen@freebsd.org>: > MT> >=20 > MT> >>=20 > MT> >>=20 > MT> >>> On 8. Jul 2019, at 17:22, Paul <devgs@ukr.net> wrote: > MT> >>>=20 > MT> >>>=20 > MT> >>>=20 > MT> >>> 8 July 2019, 17:12:21, by "Michael Tuexen" = <tuexen@freebsd.org>: > MT> >>>=20 > MT> >>>>> On 8. Jul 2019, at 15:24, Paul <devgs@ukr.net> wrote: > MT> >>>>>=20 > MT> >>>>> Hi Michael, > MT> >>>>>=20 > MT> >>>>> 8 July 2019, 15:53:15, by "Michael Tuexen" = <tuexen@freebsd.org>: > MT> >>>>>=20 > MT> >>>>>>> On 8. Jul 2019, at 12:37, Paul <devgs@ukr.net> wrote: > MT> >>>>>>>=20 > MT> >>>>>>> Hi team, > MT> >>>>>>>=20 > MT> >>>>>>> Recently we had an upgrade to 12 Stable. Immediately = after, we have started=20 > MT> >>>>>>> seeing some strange connection establishment timeouts to = some fixed number > MT> >>>>>>> of external (world) hosts. The issue was persistent and = easy to reproduce. > MT> >>>>>>> Thanks to a patience and dedication of our system engineer = we have tracked =20 > MT> >>>>>>> this issue down to a specific commit: > MT> >>>>>>>=20 > MT> >>>>>>> = https://svnweb.freebsd.org/base?view=3Drevision&revision=3D338053 > MT> >>>>>>>=20 > MT> >>>>>>> This patch was also back-ported into 11 Stable: > MT> >>>>>>>=20 > MT> >>>>>>> = https://svnweb.freebsd.org/base?view=3Drevision&revision=3D348435 > MT> >>>>>>>=20 > MT> >>>>>>> Among other things this patch changes the timestamp = allocation strategy, > MT> >>>>>>> by introducing a deterministic randomness via a hash = function that takes > MT> >>>>>>> into account a random key as well as source address, = source port, dest > MT> >>>>>>> address and dest port. As the result, timestamp offsets of = different > MT> >>>>>>> tuples (SA,SP,DA,DP) will be wildly different and will = jump from small=20 > MT> >>>>>>> to large numbers and back, as long as something in the = tuple changes. > MT> >>>>>> Hi Paul, > MT> >>>>>>=20 > MT> >>>>>> this is correct. > MT> >>>>>>=20 > MT> >>>>>> Please note that the same happens with the old method, if = two hosts with > MT> >>>>>> different uptimes are bind a consumer grade NAT. > MT> >>>>>=20 > MT> >>>>> If NAT does not replace timestamps then yes, it should be = the case. > MT> >>>>>=20 > MT> >>>>>>>=20 > MT> >>>>>>> After performing various tests of hosts that produce the = above mentioned=20 > MT> >>>>>>> issue we came to conclusion that there are some = interesting implementations=20 > MT> >>>>>>> that drop SYN packets with timestamps smaller than the = largest timestamp=20 > MT> >>>>>>> value from streams of all recent or current connections = from a specific=20 > MT> >>>>>>> address. This looks as some kind of SYN flood protection. > MT> >>>>>> This also breaks multiple hosts with different uptimes = behind a consumer > MT> >>>>>> level NAT talking to such a server. > MT> >>>>>>>=20 > MT> >>>>>>> To ensure that each external host is not going to see a = wild jumps of=20 > MT> >>>>>>> timestamp values I propose a patch that removes ports from = the equation > MT> >>>>>>> all together, when calculating the timestamp offset: > MT> >>>>>>>=20 > MT> >>>>>>> Index: sys/netinet/tcp_subr.c > MT> >>>>>>> = =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D > MT> >>>>>>> --- sys/netinet/tcp_subr.c (revision 348435) > MT> >>>>>>> +++ sys/netinet/tcp_subr.c (working copy) > MT> >>>>>>> @@ -2224,7 +2224,22 @@ > MT> >>>>>>> uint32_t > MT> >>>>>>> tcp_new_ts_offset(struct in_conninfo *inc) > MT> >>>>>>> { > MT> >>>>>>> - return (tcp_keyed_hash(inc, V_ts_offset_secret)); > MT> >>>>>>> + /*=20 > MT> >>>>>>> + * Some implementations show a strange behaviour = when a wildly random=20 > MT> >>>>>>> + * timestamps allocated for different streams. It = seems that only the > MT> >>>>>>> + * SYN packets are affected. Observed = implementations drop SYN packets > MT> >>>>>>> + * with timestamps smaller than the largest = timestamp value of all=20 > MT> >>>>>>> + * recent or current connections from specific a = address. To mitigate=20 > MT> >>>>>>> + * this we are going to ensure that each host = will always observe=20 > MT> >>>>>>> + * timestamps as increasing no matter the stream: = by dropping ports > MT> >>>>>>> + * from the equation. > MT> >>>>>>> + */=20 > MT> >>>>>>> + struct in_conninfo inc_copy =3D *inc; > MT> >>>>>>> + > MT> >>>>>>> + inc_copy.inc_fport =3D 0; > MT> >>>>>>> + inc_copy.inc_lport =3D 0; > MT> >>>>>>> + > MT> >>>>>>> + return (tcp_keyed_hash(&inc_copy, V_ts_offset_secret)); > MT> >>>>>>> } > MT> >>>>>>>=20 > MT> >>>>>>> /* > MT> >>>>>>>=20 > MT> >>>>>>> In any case, the solution of the uptime leak, implemented = in rev338053 is=20 > MT> >>>>>>> not going to suffer, because a supposed attacker is = currently able to use=20 > MT> >>>>>>> any fixed values of SP and DP, albeit not 0, anyway, to = remove them out=20 > MT> >>>>>>> of the equation. > MT> >>>>>> Can you describe how a peer can compute the uptime from two = observed timestamps? > MT> >>>>>> I don't see how you can do that... > MT> >>>>>=20 > MT> >>>>> Supposed attacker could run a script that continuously = monitors timestamps, > MT> >>>>> for example via a periodic TCP connection from a fixed local = port (eg 12345)=20 > MT> >>>>> and a fixed local address to the fixed victim's address and = port (eg 80). > MT> >>>>> Whenever large discrepancy is observed, attacker can assume = that reboot has=20 > MT> >>>>> happened (due to V_ts_offset_secret re-generation), hence = the received=20 > MT> >>>>> timestamp is considered an approximate point of reboot from = which the uptime > MT> >>>>> can be calculated, until the next reboot and so on. > MT> >>>> Ahh, I see. The patch we are talking about is not intended to = protect against > MT> >>>> continuous monitoring, which is something you can always do. = You could even > MT> >>>> watch for service availability and detect reboots. A change = of the local key > MT> >>>> would also look similar to a reboot without a temporary loss = of connectivity. > MT> >>>>=20 > MT> >>>> Thanks for the clarification. > MT> >>>>>=20 > MT> >>>>>>>=20 > MT> >>>>>>> There is the list of example hosts that we were able to = reproduce the=20 > MT> >>>>>>> issue with: > MT> >>>>>>>=20 > MT> >>>>>>> curl -v http://88.99.60.171:80 > MT> >>>>>>> curl -v http://163.172.71.252:80 > MT> >>>>>>> curl -v http://5.9.242.150:80 > MT> >>>>>>> curl -v https://185.134.205.105:443 > MT> >>>>>>> curl -v https://136.243.1.231:443 > MT> >>>>>>> curl -v https://144.76.196.4:443 > MT> >>>>>>> curl -v http://94.127.191.194:80 > MT> >>>>>>>=20 > MT> >>>>>>> To reproduce, call curl repeatedly with a same URL some = number of times.=20 > MT> >>>>>>> You are going to see some of the requests stuck in=20 > MT> >>>>>>> `* Trying XXX.XXX.XXX.XXX...` > MT> >>>>>>>=20 > MT> >>>>>>> For some reason, the easiest way to reproduce the issue is = with nc: > MT> >>>>>>>=20 > MT> >>>>>>> $ echo "foooooo" | nc -v 88.99.60.171 80 > MT> >>>>>>>=20 > MT> >>>>>>> Only a few such calls are required until one of them is = stuck on connect(): > MT> >>>>>>> issuing SYN packets with an exponential backoff. > MT> >>>>>> Thanks for providing an end-point to test with. I'll take a = look. > MT> >>>>>> Just to be clear: You are running a FreeBSD client against = one of the above > MT> >>>>>> servers and experience the problem with the new timestamp = computations. > MT> >>>>>>=20 > MT> >>>>>> You are not running arbitrary clients against a FreeBSD = server... > MT> >>>>>=20 > MT> >>>>> We are talking about FreeBSD being the client. Peers that = yield this unwanted > MT> >>>>> behaviour are unknown. Little bit of tinkering showed that = some of them run=20 > MT> >>>>> Debian: > MT> >>>>>=20 > MT> >>>>> telnet 88.99.60.171 22 > MT> >>>>> Trying 88.99.60.171... > MT> >>>>> Connected to 88.99.60.171. > MT> >>>>> Escape character is '^]'. > MT> >>>>> SSH-2.0-OpenSSH_6.7p1 Debian-5+deb8u3 > MT> >>>> Also some are hosted by Hetzner, but not all. I'll will look = into > MT> >>>> this tomorrow, since I'm on a deadline today (well it is 2am = tomorrow > MT> >>>> morning, to be precise)... > MT> >>>=20 > MT> >>> Thanks a lot, I would appreciate that. > MT> >> Hi Paul, > MT> >>=20 > MT> >> I have looked into this. > MT> >>=20 > MT> >> * The FreeBSD behaviour is the one which is specified in the = last bullet item > MT> >> in https://tools.ietf.org/html/rfc7323#section-5.4 > MT> >> It is also the one, which is RECOMMENDED in > MT> >> https://tools.ietf.org/html/rfc7323#section-7.1=20 > MT> >>=20 > MT> >> * My NAT box (a popular one in Germany) does NOT rewrite TCP = timestamps. > MT> >>=20 > MT> >> This means that the host you are referring to have some sort of = protection, > MT> >> which makes incorrect assumptions. It will also break multiple = hosts behind > MT> >> a NAT. > MT> >>=20 > MT> >> I can run > MT> >> curl -v http://88.99.60.171:80 > MT> >> in a loop without any problems from a FreeBSD head system. I = tested 1000 > MT> >> iterations or so. The TS.val is jumping up and down as = expected. > MT> >> I'm wondering why you are observing errors in this case, too. > MT> >>=20 > MT> >> However, doing something like > MT> >> echo "foooooo" | nc -v 88.99.60.171 80 > MT> >> triggers the problem. > MT> >>=20 > MT> >> So I think there is some functionality (in a middlebox or = running on the host), > MT> >> which incorrectly assume monotonic timestamps between multiple = TCP connections > MT> >> coming from the same IP address, but only in case of errors at = the application layer. > MT> >=20 > MT> > Yeah, exactly, some hosts seem to enable this only in case of an = error in HTTP > MT> > communication (some smart proxy?). However, there are some that = behave this way > MT> > regardless of errors, for example these: > MT> >=20 > MT> > curl -v https://185.134.205.105:443 > MT> > curl -v https://136.243.1.231:443 > MT> Wireshark sees an Encrypted Alert in both cases. So I guess this = is another indication > MT> of "error at the application layer". > MT> >=20 > MT> >>=20 > MT> >> Do you have any insights whether the hosts you are listed share = something in > MT> >> common. Some of them are hosted by Hetzner, but not all. > MT> >=20 > MT> > Nope. A whole set of endpoints that we have detected so far is = pretty diverse, > MT> > containing a lot of different locations geographically, as well = as different > MT> > hosters. > MT> OK. Thanks for the clarification. > MT> >=20 > MT> >>=20 > MT> >> I think in general, it is the correct thing to include the port = numbers in > MT> >> the offset computation. We might add a sysctl variable to = control the inclusion. > MT> >> This would allow interworking with broken middleboxes. > MT> >=20 > MT> > Yeah, I completely agree that these rare cases should not = dictate the implementation. > MT> > But an ability to enable a work-around via sysctl would be = greatly appreciated. > MT> > Currently we are unable to roll-out the upgrade across all = servers because of this > MT> > issue: even though it happens not so often, a lot of requests = from our users=20 > MT> > get stuck or fail all together. For example, a host = 185.134.205.105 is a kind of > MT> > social network that our proxy servers connect to so securely = access to content, > MT> > such as images, on behalf of our users. > MT> >=20 > MT> >>=20 > MT> >> Please note, this does not fix the case of multiple clients = behind a NAT. > MT> >=20 > MT> > Yeah, that's true. Fortunately we don't use NAT. > MT> >=20 > MT> >>=20 > MT> >> I'm also trying to figure out how and why Linux and Windows are = handling this. > MT> >=20 > MT> > Thanks for bothering! > MT> Will let you know what I figure out. > MT>=20 > MT> Best regards > MT> Michael > MT> >=20 > MT> >>=20 > MT> >> Best regards > MT> >> Michael > MT> >>=20 > MT> >>>=20 > MT> >>>>=20 > MT> >>>> Best regards > MT> >>>> Michael=20 > MT> >>>>>=20 > MT> >>>>>=20 > MT> >>>>>>=20 > MT> >>>>>> Best regards > MT> >>>>>> Michael > MT> >>>>>>=20 > MT> >>>>>>=20 > MT> >>>>=20 > MT> >>>>=20 > MT> >>=20 > MT> >>=20 > MT>=20 > MT> _______________________________________________ > MT> freebsd-net@freebsd.org mailing list > MT> https://lists.freebsd.org/mailman/listinfo/freebsd-net > MT> To unsubscribe, send any mail to = "freebsd-net-unsubscribe@freebsd.org" > _______________________________________________ > freebsd-net@freebsd.org mailing list > https://lists.freebsd.org/mailman/listinfo/freebsd-net > To unsubscribe, send any mail to "freebsd-net-unsubscribe@freebsd.org"
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