Daniel Borkmann b69040d8e3 net: sctp: fix panic on duplicate ASCONF chunks ... When receiving a e.g. semi-good formed connection scan in the form of ... -------------- INIT[ASCONF; ASCONF_ACK] -------------> <----------- INIT-ACK[ASCONF; ASCONF_ACK] ------------ -------------------- COOKIE-ECHO --------------------> <-------------------- COOKIE-ACK --------------------- ---------------- ASCONF_a; ASCONF_b -----------------> ... where ASCONF_a equals ASCONF_b chunk (at least both serials need to be equal), we panic an SCTP server! The problem is that good-formed ASCONF chunks that we reply with ASCONF_ACK chunks are cached per serial. Thus, when we receive a same ASCONF chunk twice (e.g. through a lost ASCONF_ACK), we do not need to process them again on the server side (that was the idea, also proposed in the RFC). Instead, we know it was cached and we just resend the cached chunk instead. So far, so good. Where things get nasty is in SCTP's side effect interpreter, that is, sctp_cmd_interpreter(): While incoming ASCONF_a (chunk = event_arg) is being marked !end_of_packet and !singleton, and we have an association context, we do not flush the outqueue the first time after processing the ASCONF_ACK singleton chunk via SCTP_CMD_REPLY. Instead, we keep it queued up, although we set local_cork to 1. Commit 2e3216cd54 changed the precedence, so that as long as we get bundled, incoming chunks we try possible bundling on outgoing queue as well. Before this commit, we would just flush the output queue. Now, while ASCONF_a's ASCONF_ACK sits in the corked outq, we continue to process the same ASCONF_b chunk from the packet. As we have cached the previous ASCONF_ACK, we find it, grab it and do another SCTP_CMD_REPLY command on it. So, effectively, we rip the chunk->list pointers and requeue the same ASCONF_ACK chunk another time. Since we process ASCONF_b, it's correctly marked with end_of_packet and we enforce an uncork, and thus flush, thus crashing the kernel. Fix it by testing if the ASCONF_ACK is currently pending and if that is the case, do not requeue it. When flushing the output queue we may relink the chunk for preparing an outgoing packet, but eventually unlink it when it's copied into the skb right before transmission. Joint work with Vlad Yasevich. Fixes: 2e3216cd54 ("sctp: Follow security requirement of responding with 1 packet") Signed-off-by: Daniel Borkmann <dborkman@redhat.com> Signed-off-by: Vlad Yasevich <vyasevich@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>		2014-10-14 12:46:22 -04:00
..
auth.h	include/net/: Fix FSF address in file headers	2013-12-06 12:37:56 -05:00
checksum.h	include/net/: Fix FSF address in file headers	2013-12-06 12:37:56 -05:00
command.h	sctp: handle association restarts when the socket is closed.	2014-10-06 00:21:45 -04:00
constants.h	net: sctp: Rename SCTP_XMIT_NAGLE_DELAY to SCTP_XMIT_DELAY	2014-07-22 13:32:11 -07:00
sctp.h	net: sctp: fix panic on duplicate ASCONF chunks	2014-10-14 12:46:22 -04:00
sm.h	net: sctp: fix skb_over_panic when receiving malformed ASCONF chunks	2014-10-14 12:46:22 -04:00
structs.h	sctp: Fixup v4mapped behaviour to comply with Sock API	2014-07-31 21:49:06 -07:00
tsnmap.h	sctp: Fix FSF address in file headers	2013-12-06 12:37:56 -05:00
ulpevent.h	net: sctp: implement rfc6458, 5.3.6. SCTP_NXTINFO cmsg support	2014-07-16 14:40:03 -07:00
ulpqueue.h	sctp: Fix FSF address in file headers	2013-12-06 12:37:56 -05:00