![Alexander Sverdlin](/assets/img/avatar_default.png)
net: sctp: Fix data chunk fragmentation for MTU values which are not multiple of 4 Initially the problem was observed with ipsec, but later it became clear that SCTP data chunk fragmentation algorithm has problems with MTU values which are not multiple of 4. Test program was used which just transmits 2000 bytes long packets to other host. tcpdump was used to observe re-fragmentation in IP layer after SCTP already fragmented data chunks. With MTU 1500: 12:54:34.082904 IP (tos 0x2,ECT(0), ttl 64, id 0, offset 0, flags [DF], proto SCTP (132), length 1500) 10.151.38.153.39303 > 10.151.24.91.54321: sctp (1) [DATA] (B) [TSN: 2366088589] [SID: 0] [SSEQ 1] [PPID 0x0] 12:54:34.082933 IP (tos 0x2,ECT(0), ttl 64, id 0, offset 0, flags [DF], proto SCTP (132), length 596) 10.151.38.153.39303 > 10.151.24.91.54321: sctp (1) [DATA] (E) [TSN: 2366088590] [SID: 0] [SSEQ 1] [PPID 0x0] 12:54:34.090576 IP (tos 0x2,ECT(0), ttl 63, id 0, offset 0, flags [DF], proto SCTP (132), length 48) 10.151.24.91.54321 > 10.151.38.153.39303: sctp (1) [SACK] [cum ack 2366088590] [a_rwnd 79920] [#gap acks 0] [#dup tsns 0] With MTU 1499: 13:02:49.955220 IP (tos 0x2,ECT(0), ttl 64, id 48215, offset 0, flags [+], proto SCTP (132), length 1492) 10.151.38.153.39084 > 10.151.24.91.54321: sctp[|sctp] 13:02:49.955249 IP (tos 0x2,ECT(0), ttl 64, id 48215, offset 1472, flags [none], proto SCTP (132), length 28) 10.151.38.153 > 10.151.24.91: ip-proto-132 13:02:49.955262 IP (tos 0x2,ECT(0), ttl 64, id 0, offset 0, flags [DF], proto SCTP (132), length 600) 10.151.38.153.39084 > 10.151.24.91.54321: sctp (1) [DATA] (E) [TSN: 404355346] [SID: 0] [SSEQ 1] [PPID 0x0] 13:02:49.956770 IP (tos 0x2,ECT(0), ttl 63, id 0, offset 0, flags [DF], proto SCTP (132), length 48) 10.151.24.91.54321 > 10.151.38.153.39084: sctp (1) [SACK] [cum ack 404355346] [a_rwnd 79920] [#gap acks 0] [#dup tsns 0] Here problem in data portion limit calculation leads to re-fragmentation in IP, which is sub-optimal. The problem is max_data initial value, which doesn't take into account the fact, that data chunk must be padded to 4-bytes boundary. It's enough to correct max_data, because all later adjustments are correctly aligned to 4-bytes boundary. After the fix is applied, everything is fragmented correctly for uneven MTUs: 15:16:27.083881 IP (tos 0x2,ECT(0), ttl 64, id 0, offset 0, flags [DF], proto SCTP (132), length 1496) 10.151.38.153.53417 > 10.151.24.91.54321: sctp (1) [DATA] (B) [TSN: 3077098183] [SID: 0] [SSEQ 1] [PPID 0x0] 15:16:27.083907 IP (tos 0x2,ECT(0), ttl 64, id 0, offset 0, flags [DF], proto SCTP (132), length 600) 10.151.38.153.53417 > 10.151.24.91.54321: sctp (1) [DATA] (E) [TSN: 3077098184] [SID: 0] [SSEQ 1] [PPID 0x0] 15:16:27.085640 IP (tos 0x2,ECT(0), ttl 63, id 0, offset 0, flags [DF], proto SCTP (132), length 48) 10.151.24.91.54321 > 10.151.38.153.53417: sctp (1) [SACK] [cum ack 3077098184] [a_rwnd 79920] [#gap acks 0] [#dup tsns 0] The bug was there for years already, but - is a performance issue, the packets are still transmitted - doesn't show up with default MTU 1500, but possibly with ipsec (MTU 1438) Signed-off-by: Alexander Sverdlin <alexander.sverdlin@nsn.com> Acked-by: Vlad Yasevich <vyasevich@gmail.com> Acked-by: Neil Horman <nhorman@tuxdriver.com> Signed-off-by: David S. Miller <davem@davemloft.net>
368 lines
9.6 KiB
C
368 lines
9.6 KiB
C
/* SCTP kernel implementation
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* (C) Copyright IBM Corp. 2003, 2004
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*
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* This file is part of the SCTP kernel implementation
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*
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* This file contains the code relating the chunk abstraction.
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*
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* This SCTP implementation is free software;
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* you can redistribute it and/or modify it under the terms of
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* the GNU General Public License as published by
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* the Free Software Foundation; either version 2, or (at your option)
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* any later version.
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*
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* This SCTP implementation is distributed in the hope that it
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* will be useful, but WITHOUT ANY WARRANTY; without even the implied
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* ************************
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* warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
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* See the GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with GNU CC; see the file COPYING. If not, write to
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* the Free Software Foundation, 59 Temple Place - Suite 330,
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* Boston, MA 02111-1307, USA.
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*
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* Please send any bug reports or fixes you make to the
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* email address(es):
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* lksctp developers <linux-sctp@vger.kernel.org>
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*
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* Written or modified by:
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* Jon Grimm <jgrimm@us.ibm.com>
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* Sridhar Samudrala <sri@us.ibm.com>
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*/
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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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#include <linux/types.h>
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#include <linux/kernel.h>
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#include <linux/net.h>
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#include <linux/inet.h>
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#include <linux/skbuff.h>
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#include <linux/slab.h>
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#include <net/sock.h>
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#include <net/sctp/sctp.h>
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#include <net/sctp/sm.h>
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/* This file is mostly in anticipation of future work, but initially
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* populate with fragment tracking for an outbound message.
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*/
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/* Initialize datamsg from memory. */
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static void sctp_datamsg_init(struct sctp_datamsg *msg)
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{
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atomic_set(&msg->refcnt, 1);
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msg->send_failed = 0;
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msg->send_error = 0;
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msg->can_abandon = 0;
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msg->can_delay = 1;
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msg->expires_at = 0;
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INIT_LIST_HEAD(&msg->chunks);
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}
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/* Allocate and initialize datamsg. */
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static struct sctp_datamsg *sctp_datamsg_new(gfp_t gfp)
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{
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struct sctp_datamsg *msg;
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msg = kmalloc(sizeof(struct sctp_datamsg), gfp);
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if (msg) {
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sctp_datamsg_init(msg);
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SCTP_DBG_OBJCNT_INC(datamsg);
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}
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return msg;
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}
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void sctp_datamsg_free(struct sctp_datamsg *msg)
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{
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struct sctp_chunk *chunk;
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/* This doesn't have to be a _safe vairant because
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* sctp_chunk_free() only drops the refs.
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*/
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list_for_each_entry(chunk, &msg->chunks, frag_list)
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sctp_chunk_free(chunk);
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sctp_datamsg_put(msg);
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}
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/* Final destructruction of datamsg memory. */
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static void sctp_datamsg_destroy(struct sctp_datamsg *msg)
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{
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struct list_head *pos, *temp;
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struct sctp_chunk *chunk;
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struct sctp_sock *sp;
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struct sctp_ulpevent *ev;
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struct sctp_association *asoc = NULL;
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int error = 0, notify;
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/* If we failed, we may need to notify. */
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notify = msg->send_failed ? -1 : 0;
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/* Release all references. */
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list_for_each_safe(pos, temp, &msg->chunks) {
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list_del_init(pos);
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chunk = list_entry(pos, struct sctp_chunk, frag_list);
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/* Check whether we _really_ need to notify. */
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if (notify < 0) {
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asoc = chunk->asoc;
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if (msg->send_error)
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error = msg->send_error;
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else
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error = asoc->outqueue.error;
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sp = sctp_sk(asoc->base.sk);
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notify = sctp_ulpevent_type_enabled(SCTP_SEND_FAILED,
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&sp->subscribe);
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}
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/* Generate a SEND FAILED event only if enabled. */
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if (notify > 0) {
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int sent;
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if (chunk->has_tsn)
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sent = SCTP_DATA_SENT;
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else
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sent = SCTP_DATA_UNSENT;
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ev = sctp_ulpevent_make_send_failed(asoc, chunk, sent,
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error, GFP_ATOMIC);
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if (ev)
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sctp_ulpq_tail_event(&asoc->ulpq, ev);
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}
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sctp_chunk_put(chunk);
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}
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SCTP_DBG_OBJCNT_DEC(datamsg);
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kfree(msg);
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}
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/* Hold a reference. */
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static void sctp_datamsg_hold(struct sctp_datamsg *msg)
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{
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atomic_inc(&msg->refcnt);
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}
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/* Release a reference. */
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void sctp_datamsg_put(struct sctp_datamsg *msg)
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{
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if (atomic_dec_and_test(&msg->refcnt))
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sctp_datamsg_destroy(msg);
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}
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/* Assign a chunk to this datamsg. */
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static void sctp_datamsg_assign(struct sctp_datamsg *msg, struct sctp_chunk *chunk)
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{
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sctp_datamsg_hold(msg);
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chunk->msg = msg;
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}
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/* A data chunk can have a maximum payload of (2^16 - 20). Break
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* down any such message into smaller chunks. Opportunistically, fragment
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* the chunks down to the current MTU constraints. We may get refragmented
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* later if the PMTU changes, but it is _much better_ to fragment immediately
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* with a reasonable guess than always doing our fragmentation on the
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* soft-interrupt.
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*/
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struct sctp_datamsg *sctp_datamsg_from_user(struct sctp_association *asoc,
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struct sctp_sndrcvinfo *sinfo,
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struct msghdr *msgh, int msg_len)
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{
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int max, whole, i, offset, over, err;
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int len, first_len;
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int max_data;
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struct sctp_chunk *chunk;
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struct sctp_datamsg *msg;
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struct list_head *pos, *temp;
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__u8 frag;
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msg = sctp_datamsg_new(GFP_KERNEL);
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if (!msg)
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return ERR_PTR(-ENOMEM);
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/* Note: Calculate this outside of the loop, so that all fragments
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* have the same expiration.
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*/
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if (sinfo->sinfo_timetolive) {
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/* sinfo_timetolive is in milliseconds */
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msg->expires_at = jiffies +
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msecs_to_jiffies(sinfo->sinfo_timetolive);
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msg->can_abandon = 1;
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pr_debug("%s: msg:%p expires_at:%ld jiffies:%ld\n", __func__,
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msg, msg->expires_at, jiffies);
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}
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/* This is the biggest possible DATA chunk that can fit into
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* the packet
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*/
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max_data = (asoc->pathmtu -
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sctp_sk(asoc->base.sk)->pf->af->net_header_len -
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sizeof(struct sctphdr) - sizeof(struct sctp_data_chunk)) & ~3;
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max = asoc->frag_point;
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/* If the the peer requested that we authenticate DATA chunks
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* we need to accound for bundling of the AUTH chunks along with
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* DATA.
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*/
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if (sctp_auth_send_cid(SCTP_CID_DATA, asoc)) {
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struct sctp_hmac *hmac_desc = sctp_auth_asoc_get_hmac(asoc);
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if (hmac_desc)
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max_data -= WORD_ROUND(sizeof(sctp_auth_chunk_t) +
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hmac_desc->hmac_len);
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}
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/* Now, check if we need to reduce our max */
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if (max > max_data)
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max = max_data;
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whole = 0;
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first_len = max;
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/* Check to see if we have a pending SACK and try to let it be bundled
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* with this message. Do this if we don't have any data queued already.
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* To check that, look at out_qlen and retransmit list.
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* NOTE: we will not reduce to account for SACK, if the message would
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* not have been fragmented.
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*/
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if (timer_pending(&asoc->timers[SCTP_EVENT_TIMEOUT_SACK]) &&
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asoc->outqueue.out_qlen == 0 &&
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list_empty(&asoc->outqueue.retransmit) &&
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msg_len > max)
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max_data -= WORD_ROUND(sizeof(sctp_sack_chunk_t));
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/* Encourage Cookie-ECHO bundling. */
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if (asoc->state < SCTP_STATE_COOKIE_ECHOED)
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max_data -= SCTP_ARBITRARY_COOKIE_ECHO_LEN;
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/* Now that we adjusted completely, reset first_len */
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if (first_len > max_data)
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first_len = max_data;
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/* Account for a different sized first fragment */
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if (msg_len >= first_len) {
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msg_len -= first_len;
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whole = 1;
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msg->can_delay = 0;
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}
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/* How many full sized? How many bytes leftover? */
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whole += msg_len / max;
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over = msg_len % max;
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offset = 0;
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if ((whole > 1) || (whole && over))
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SCTP_INC_STATS_USER(sock_net(asoc->base.sk), SCTP_MIB_FRAGUSRMSGS);
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/* Create chunks for all the full sized DATA chunks. */
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for (i=0, len=first_len; i < whole; i++) {
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frag = SCTP_DATA_MIDDLE_FRAG;
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if (0 == i)
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frag |= SCTP_DATA_FIRST_FRAG;
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if ((i == (whole - 1)) && !over) {
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frag |= SCTP_DATA_LAST_FRAG;
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/* The application requests to set the I-bit of the
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* last DATA chunk of a user message when providing
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* the user message to the SCTP implementation.
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*/
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if ((sinfo->sinfo_flags & SCTP_EOF) ||
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(sinfo->sinfo_flags & SCTP_SACK_IMMEDIATELY))
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frag |= SCTP_DATA_SACK_IMM;
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}
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chunk = sctp_make_datafrag_empty(asoc, sinfo, len, frag, 0);
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if (!chunk) {
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err = -ENOMEM;
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goto errout;
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}
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err = sctp_user_addto_chunk(chunk, offset, len, msgh->msg_iov);
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if (err < 0)
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goto errout_chunk_free;
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offset += len;
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/* Put the chunk->skb back into the form expected by send. */
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__skb_pull(chunk->skb, (__u8 *)chunk->chunk_hdr
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- (__u8 *)chunk->skb->data);
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sctp_datamsg_assign(msg, chunk);
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list_add_tail(&chunk->frag_list, &msg->chunks);
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/* The first chunk, the first chunk was likely short
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* to allow bundling, so reset to full size.
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*/
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if (0 == i)
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len = max;
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}
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/* .. now the leftover bytes. */
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if (over) {
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if (!whole)
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frag = SCTP_DATA_NOT_FRAG;
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else
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frag = SCTP_DATA_LAST_FRAG;
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if ((sinfo->sinfo_flags & SCTP_EOF) ||
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(sinfo->sinfo_flags & SCTP_SACK_IMMEDIATELY))
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frag |= SCTP_DATA_SACK_IMM;
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chunk = sctp_make_datafrag_empty(asoc, sinfo, over, frag, 0);
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if (!chunk) {
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err = -ENOMEM;
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goto errout;
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}
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err = sctp_user_addto_chunk(chunk, offset, over,msgh->msg_iov);
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/* Put the chunk->skb back into the form expected by send. */
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__skb_pull(chunk->skb, (__u8 *)chunk->chunk_hdr
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- (__u8 *)chunk->skb->data);
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if (err < 0)
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goto errout_chunk_free;
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sctp_datamsg_assign(msg, chunk);
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list_add_tail(&chunk->frag_list, &msg->chunks);
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}
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return msg;
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errout_chunk_free:
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sctp_chunk_free(chunk);
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errout:
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list_for_each_safe(pos, temp, &msg->chunks) {
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list_del_init(pos);
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chunk = list_entry(pos, struct sctp_chunk, frag_list);
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sctp_chunk_free(chunk);
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}
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sctp_datamsg_put(msg);
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return ERR_PTR(err);
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}
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/* Check whether this message has expired. */
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int sctp_chunk_abandoned(struct sctp_chunk *chunk)
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{
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struct sctp_datamsg *msg = chunk->msg;
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if (!msg->can_abandon)
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return 0;
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if (time_after(jiffies, msg->expires_at))
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return 1;
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return 0;
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}
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/* This chunk (and consequently entire message) has failed in its sending. */
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void sctp_chunk_fail(struct sctp_chunk *chunk, int error)
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{
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chunk->msg->send_failed = 1;
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chunk->msg->send_error = error;
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}
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