On Tue, Jul 16, 2019 at 10:49 PM Marek Majkowski <marek@xxxxxxxxxxxxxx> wrote: > > Morning, > > My poor man's fuzzer found something interesting in SCTP. It seems > like creating large number of SCTP sockets + some magic dance, upsets > a memory subsystem related to SCTP. The sequence: > > - create SCTP socket > - call setsockopts (SCTP_EVENTS) > - call bind(::1, port) > - call sendmsg(long buffer, MSG_CONFIRM, ::1, port) > - close SCTP socket > - repeat couple thousand times > > Full code: > https://gist.github.com/majek/bd083dae769804d39134ce01f4f802bb#file-test_sctp-c > > I'm running it on virtme the simplest way: > $ virtme-run --show-boot-console --rw --pwd --kimg bzImage --memory > 512M --script-sh ./test_sctp > > Originally I was running it inside net namespace, and just having a > localhost interface is sufficient to trigger the problem. > > Kernel is 5.2.1 (with KASAN and such, but that shouldn't be a factor). > In some tests I saw a message that might indicate something funny > hitting neighbor table: > > neighbour: ndisc_cache: neighbor table overflow! > > I'm not addr-decoding the stack trace, since it seems unrelated to the > root cause. > > Cheers, > Marek I _think_ this is an 'expected' peculiarity of SCTP on loopback - you test_sctp.c ends up creating actual associations to itself on the same socket (you can test safely by reducing the port range (say 30000-32000) and setting the for-loop-clause to 'run < 1') You'll see a bunch of associations established like the following (note that I(kernel) was dropping packets for this capture - even with /only/ 2000 sockets used...) $ tshark -r sctp.pcap -Y 'sctp.assoc_index==4' 21 0.000409127 ::1 → ::1 SCTP INIT 22 0.000436281 ::1 → ::1 SCTP INIT_ACK 23 0.000442106 ::1 → ::1 SCTP COOKIE_ECHO 24 0.000463007 ::1 → ::1 SCTP COOKIE_ACK DATA (Message Fragment) presumably your close() happens here and we enter SHUTDOWN-PENDING, where we wait for pending data to be acknowledged, I'm not convinced that we shouldn't be SACK'ing the data from the 'peer' at this point - but for whatever reason, we aren't. We then run thru path-max-retrans, and finally ABORT (the abort indication also shows the PMR-exceeded indication in the 'Cause Information') 25 0.000476083 ::1 → ::1 SCTP SACK 13619 3.017788109 ::1 → ::1 SCTP DATA (retransmission) 14022 3.222690889 ::1 → ::1 SCTP SACK 18922 21.938217449 ::1 → ::1 SCTP SACK 33476 69.831029904 ::1 → ::1 SCTP HEARTBEAT 33561 69.831310796 ::1 → ::1 SCTP HEARTBEAT_ACK 40816 94.102667600 ::1 → ::1 SCTP SACK 40910 95.942741287 ::1 → ::1 SCTP DATA (retransmission) 41039 96.152023010 ::1 → ::1 SCTP SACK 41100 100.182685237 ::1 → ::1 SCTP SACK 41212 108.230746764 ::1 → ::1 SCTP DATA (retransmission) 41345 108.439061392 ::1 → ::1 SCTP SACK 41407 116.422688507 ::1 → ::1 SCTP HEARTBEAT 41413 116.423183124 ::1 → ::1 SCTP HEARTBEAT_ACK 41494 124.823749255 ::1 → ::1 SCTP SACK 41576 126.663648718 ::1 → ::1 SCTP ABORT With your entire 512M - you'd only have about 16KB for each of these 31K associations tops, I suspect that having a 64KB pending data chunk (fragmented ULP msg) for each association for >= 90s is what is exhausting memory here - although I'm sure Neil or Michael will be along to correct me ;-) What's interesting - as you reduce the payload size - we end up bundling DATA from the 'initiator' side (in COOKIE ECHO) - and everything works as expected... (the SACK here is for the bundled DATA chunks TSN. mlashley@duality /tmp $ tshark -r /tmp/sctp_index4_10K.pcap 1 0.000000000 ::1 → ::1 SCTP INIT 2 0.000014491 ::1 → ::1 SCTP INIT_ACK 3 0.000024190 ::1 → ::1 SCTP COOKIE_ECHO DATA 4 0.000034833 ::1 → ::1 SCTP COOKIE_ACK 5 0.000040646 ::1 → ::1 SCTP SACK 6 0.000050287 ::1 → ::1 SCTP ABORT In short - the SCTP associations /can/ persist after user-space calls close() whilst there is outstanding data (for path.max.retrans * rto-with-doubling[due to T3-rtx expiry]) (My tests on 5.2.0 as it is what I had to hand...) Cheers, malc.
