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Sun, 26 Apr 2026 07:48:57 -0700 (PDT) Received: from wsfd-netdev58.anl.eng.rdu2.dc.redhat.com ([66.187.232.140]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-8b02aebc655sm232579146d6.48.2026.04.26.07.48.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 26 Apr 2026 07:48:56 -0700 (PDT) From: Xin Long To: network dev , netfilter-devel@vger.kernel.org, linux-sctp@vger.kernel.org Cc: davem@davemloft.net, kuba@kernel.org, Eric Dumazet , Paolo Abeni , Simon Horman , Pablo Neira Ayuso , Florian Westphal , Phil Sutter , Marcelo Ricardo Leitner , Yi Chen Subject: [PATCH net v2 0/2] sctp: fix a vtag verification failure caused by stale INITs Date: Sun, 26 Apr 2026 10:46:39 -0400 Message-ID: X-Mailer: git-send-email 2.47.1 Precedence: bulk X-Mailing-List: linux-sctp@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Similar to Scenario B in commit 8e56b063c865 ( netfilter: handle the connecting collision properly in nf_conntrack_proto_sctp"): Scenario B: INIT_ACK is delayed until the peer completes its own handshake 192.168.1.2 > 192.168.1.1: sctp (1) [INIT] [init tag: 3922216408] 192.168.1.1 > 192.168.1.2: sctp (1) [INIT] [init tag: 144230885] 192.168.1.2 > 192.168.1.1: sctp (1) [INIT ACK] [init tag: 3922216408] 192.168.1.1 > 192.168.1.2: sctp (1) [COOKIE ECHO] 192.168.1.2 > 192.168.1.1: sctp (1) [COOKIE ACK] 192.168.1.1 > 192.168.1.2: sctp (1) [INIT ACK] [init tag: 3914796021] * There is another case: Scenario F: INIT is delayed until the peer completes its own handshake 192.168.1.2 > 192.168.1.1: sctp (1) [INIT] [init tag: 3922216408] (OVS upcall) 192.168.1.1 > 192.168.1.2: sctp (1) [INIT] [init tag: 144230885] 192.168.1.2 > 192.168.1.1: sctp (1) [INIT ACK] [init tag: 3922216408] 192.168.1.1 > 192.168.1.2: sctp (1) [COOKIE ECHO] 192.168.1.2 > 192.168.1.1: sctp (1) [COOKIE ACK] 192.168.1.2 > 192.168.1.1: sctp (1) [INIT] [init tag: 3922216408] (delayed) 192.168.1.1 > 192.168.1.2: sctp (1) [INIT ACK] [init tag: 3914796021] * In this case, the delayed INIT (e.g. due to OVS upcall) is recorded by conntrack, which prevents vtag verification from dropping the unexpected INIT-ACK in nf_conntrack_sctp_packet(): vtag = ct->proto.sctp.vtag[!dir]; if (!ct->proto.sctp.init[!dir] && vtag && vtag != ih->init_tag) goto out_unlock; This happens because ct->proto.sctp.init[!dir] is set by the delayed INIT, even though it is stale. Fix this in two parts: - In netfilter: Do not record INITs whose init_tag matches the peer vtag, as they carry no new handshake state in the 1st patch. - In SCTP: Prevent endpoints from responding to such INITs with INIT-ACK, ensuring correctness even when middleboxes lack the netfilter fix in the 2nd patch. A follow-up selftest for this scenario will be posted in a separate patch by Yi Chen. Xin Long (2): netfilter: skip recording stale or retransmitted INIT sctp: discard stale INIT after handshake completion net/netfilter/nf_conntrack_proto_sctp.c | 10 +++++++--- net/sctp/sm_statefuns.c | 6 ++++++ 2 files changed, 13 insertions(+), 3 deletions(-) -- 2.47.1