From 8c98653f05534acd1cb07ea4929702a3659177d1 Mon Sep 17 00:00:00 2001 From: Daniel Borkmann Date: Fri, 1 Feb 2013 04:37:43 +0000 Subject: [PATCH] sctp: sctp_close: fix release of bindings for deferred call_rcu's It seems due to RCU usage, i.e. within SCTP's address binding list, a, say, ``behavioral change'' was introduced which does actually not conform to the RFC anymore. In particular consider the following (fictional) scenario to demonstrate this: do: Two SOCK_SEQPACKET-style sockets are opened (S1, S2) S1 is bound to 127.0.0.1, port 1024 [server] S2 is bound to 127.0.0.1, port 1025 [client] listen(2) is invoked on S1 From S2 we call one sendmsg(2) with msg.msg_name and msg.msg_namelen parameters set to the server's address S1, S2 are closed goto do The first pass of this loop passes successful, while the second round fails during binding of S1 (address still in use). What is happening? In the first round, the initial handshake is being done, and, at the time close(2) is called on S1, a non-graceful shutdown is performed via ABORT since in S1's receive queue an unprocessed packet is present, thus stating an error condition. This can be considered as a correct behavior. During close also all bound addresses are freed, thus nothing *must* be active anymore. In reference to RFC2960: After checking the Verification Tag, the receiving endpoint shall remove the association from its record, and shall report the termination to its upper layer. (9.1 Abort of an Association) Also, no half-open states are supported, thus after an ungraceful shutdown, we leave nothing behind. However, this seems not to be happening though. In a real-world scenario, this is exactly where it breaks the lksctp-tools functional test suite, *for instance*: ./test_sockopt test_sockopt.c 1 PASS : getsockopt(SCTP_STATUS) on a socket with no assoc test_sockopt.c 2 PASS : getsockopt(SCTP_STATUS) test_sockopt.c 3 PASS : getsockopt(SCTP_STATUS) with invalid associd test_sockopt.c 4 PASS : getsockopt(SCTP_STATUS) with NULL associd test_sockopt.c 5 BROK : bind: Address already in use The underlying problem is that sctp_endpoint_destroy() hasn't been triggered yet while the next bind attempt is being done. It will be triggered eventually (but too late) by sctp_transport_destroy_rcu() after one RCU grace period: sctp_transport_destroy() sctp_transport_destroy_rcu() ----. sctp_association_put() [*] <--+--> sctp_packet_free() sctp_association_destroy() [...] sctp_endpoint_put() skb->destructor sctp_endpoint_destroy() sctp_wfree() sctp_bind_addr_free() sctp_association_put() [*] Thus, we move out the condition with sctp_association_put() as well as the sctp_packet_free() invocation and the issue can be solved. We also better free the SCTP chunks first before putting the ref of the association. With this patch, the example above (which simulates a similar scenario as in the implementation of this test case) and therefore also the test suite run successfully through. Tested by myself. Cc: Vlad Yasevich Signed-off-by: Daniel Borkmann Acked-by: Vlad Yasevich Acked-by: Neil Horman Signed-off-by: David S. Miller --- net/sctp/transport.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) diff --git a/net/sctp/transport.c b/net/sctp/transport.c index 4e45bb68aef0..ca5331cc1ed2 100644 --- a/net/sctp/transport.c +++ b/net/sctp/transport.c @@ -168,10 +168,6 @@ static void sctp_transport_destroy_rcu(struct rcu_head *head) struct sctp_transport *transport; transport = container_of(head, struct sctp_transport, rcu); - if (transport->asoc) - sctp_association_put(transport->asoc); - - sctp_packet_free(&transport->packet); dst_release(transport->dst); kfree(transport); @@ -186,6 +182,11 @@ static void sctp_transport_destroy(struct sctp_transport *transport) SCTP_ASSERT(transport->dead, "Transport is not dead", return); call_rcu(&transport->rcu, sctp_transport_destroy_rcu); + + sctp_packet_free(&transport->packet); + + if (transport->asoc) + sctp_association_put(transport->asoc); } /* Start T3_rtx timer if it is not already running and update the heartbeat -- GitLab