On Fri, Dec 22, 2017 at 05:04:37PM -0200, Marcelo Ricardo Leitner wrote: > On Fri, Dec 22, 2017 at 04:28:07PM -0200, Marcelo Ricardo Leitner wrote: > > On Fri, Dec 22, 2017 at 11:58:08AM +0100, Dmitry Vyukov wrote: > > ... > > > > Same with this one, perhaps related to / fixed by: > > > > http://patchwork.ozlabs.org/patch/850957/ > > > > > > > > > > > > > > > > Looking at the log, this one seems to be an infinite loop in SCTP code > > > with console output in it. Kernel is busy printing gazilion of: > > > > > > [ 176.491099] sctp: sctp_transport_update_pmtu: Reported pmtu 508 too > > > low, using default minimum of 512 > > > ** 110 printk messages dropped ** > > > [ 176.503409] sctp: sctp_transport_update_pmtu: Reported pmtu 508 too > > > low, using default minimum of 512 > > > ** 103 printk messages dropped ** > > > ... > > > [ 246.742374] sctp: sctp_transport_update_pmtu: Reported pmtu 508 too > > > low, using default minimum of 512 > > > [ 246.742484] sctp: sctp_transport_update_pmtu: Reported pmtu 508 too > > > low, using default minimum of 512 > > > [ 246.742590] sctp: sctp_transport_update_pmtu: Reported pmtu 508 too > > > low, using default minimum of 512 > > > > > > Looks like a different issue. > > > > > > > Oh. I guess this is caused by the interface having a MTU smaller than > > SCTP_DEFAULT_MINSEGMENT (512), as the icmp frag needed handler > > (sctp_icmp_frag_needed) will trigger an instant retransmission. > > But as the MTU is smaller, SCTP won't update it, but will issue the > > retransmission anyway. > > > > I will test this soon. Should be fairly easy to trigger it. > > Reproduced it. > > netns A veth0(1500) - veth1(1500) B veth2(508) - veth3(508) C > > When A sends a sctp packet bigger than 508, it triggers the issue as B > will reply a icmp frag needed with a size that sctp won't accept but > will retransmit anyway. > syzbot hasn't encountered this hang again (although, it just happened once in the first place). I assume it was fixed by commit b6c5734db070, so telling syzbot this: #syz fix: sctp: fix the handling of ICMP Frag Needed for too small MTUs - Eric -- To unsubscribe from this list: send the line "unsubscribe linux-sctp" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
