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[81.201.48.25]) by smtp.googlemail.com with ESMTPSA id by8sm648864edb.49.2020.11.05.02.42.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 05 Nov 2020 02:42:28 -0800 (PST) From: Petr Malat To: linux-sctp@vger.kernel.org Cc: Petr Malat , Vlad Yasevich , Neil Horman , Marcelo Ricardo Leitner , "David S. Miller" , Jakub Kicinski , netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] sctp: Fix sending when PMTU is less than SCTP_DEFAULT_MINSEGMENT Date: Thu, 5 Nov 2020 11:39:47 +0100 Message-Id: <20201105103946.18771-1-oss@malat.biz> X-Mailer: git-send-email 2.20.1 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org Function sctp_dst_mtu() never returns lower MTU than SCTP_TRUNC4(SCTP_DEFAULT_MINSEGMENT) even when the actual MTU is less, in which case we rely on the IP fragmentation and must enable it. Signed-off-by: Petr Malat --- net/sctp/output.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/net/sctp/output.c b/net/sctp/output.c index 1441eaf460bb..87a96cf6bfa4 100644 --- a/net/sctp/output.c +++ b/net/sctp/output.c @@ -552,6 +552,7 @@ int sctp_packet_transmit(struct sctp_packet *packet, gfp_t gfp) struct sk_buff *head; struct sctphdr *sh; struct sock *sk; + u32 pmtu; pr_debug("%s: packet:%p\n", __func__, packet); if (list_empty(&packet->chunk_list)) @@ -559,6 +560,13 @@ int sctp_packet_transmit(struct sctp_packet *packet, gfp_t gfp) chunk = list_entry(packet->chunk_list.next, struct sctp_chunk, list); sk = chunk->skb->sk; + /* Fragmentation on the IP level if the actual PMTU could be less + * than SCTP_DEFAULT_MINSEGMENT. See sctp_dst_mtu(). + */ + pmtu = tp->asoc ? tp->asoc->pathmtu : tp->pathmtu; + if (pmtu <= SCTP_DEFAULT_MINSEGMENT) + packet->ipfragok = 1; + /* check gso */ if (packet->size > tp->pathmtu && !packet->ipfragok) { if (!sk_can_gso(sk)) {