This is a note to let you know that I've just added the patch titled
mptcp: Do TCP fallback on early DSS checksum failure
to the 5.17-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
mptcp-do-tcp-fallback-on-early-dss-checksum-failure.patch
and it can be found in the queue-5.17 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From ae66fb2ba6c3dcaf8b9612b65aa949a1a4bed150 Mon Sep 17 00:00:00 2001
From: Mat Martineau <mathew.j.martineau@xxxxxxxxxxxxxxx>
Date: Tue, 17 May 2022 11:02:12 -0700
Subject: mptcp: Do TCP fallback on early DSS checksum failure
From: Mat Martineau <mathew.j.martineau@xxxxxxxxxxxxxxx>
commit ae66fb2ba6c3dcaf8b9612b65aa949a1a4bed150 upstream.
RFC 8684 section 3.7 describes several opportunities for a MPTCP
connection to "fall back" to regular TCP early in the connection
process, before it has been confirmed that MPTCP options can be
successfully propagated on all SYN, SYN/ACK, and data packets. If a peer
acknowledges the first received data packet with a regular TCP header
(no MPTCP options), fallback is allowed.
If the recipient of that first data packet finds a MPTCP DSS checksum
error, this provides an opportunity to fail gracefully with a TCP
fallback rather than resetting the connection (as might happen if a
checksum failure were detected later).
This commit modifies the checksum failure code to attempt fallback on
the initial subflow of a MPTCP connection, only if it's a failure in the
first data mapping. In cases where the peer initiates the connection,
requests checksums, is the first to send data, and the peer is sending
incorrect checksums (see
https://github.com/multipath-tcp/mptcp_net-next/issues/275), this allows
the connection to proceed as TCP rather than reset.
Fixes: dd8bcd1768ff ("mptcp: validate the data checksum")
Acked-by: Paolo Abeni <pabeni@xxxxxxxxxx>
Signed-off-by: Mat Martineau <mathew.j.martineau@xxxxxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
[mathew.j.martineau: backport: Resolved bitfield conflict in protocol.h]
Signed-off-by: Mat Martineau <mathew.j.martineau@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
net/mptcp/protocol.h | 3 ++-
net/mptcp/subflow.c | 21 ++++++++++++++++++---
2 files changed, 20 insertions(+), 4 deletions(-)
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -442,7 +442,8 @@ struct mptcp_subflow_context {
rx_eof : 1,
can_ack : 1, /* only after processing the remote a key */
disposable : 1, /* ctx can be free at ulp release time */
- stale : 1; /* unable to snd/rcv data, do not use for xmit */
+ stale : 1, /* unable to snd/rcv data, do not use for xmit */
+ valid_csum_seen : 1; /* at least one csum validated */
enum mptcp_data_avail data_avail;
u32 remote_nonce;
u64 thmac;
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -913,11 +913,14 @@ static enum mapping_status validate_data
subflow->map_data_csum);
if (unlikely(csum)) {
MPTCP_INC_STATS(sock_net(ssk), MPTCP_MIB_DATACSUMERR);
- subflow->send_mp_fail = 1;
- MPTCP_INC_STATS(sock_net(ssk), MPTCP_MIB_MPFAILTX);
+ if (subflow->mp_join || subflow->valid_csum_seen) {
+ subflow->send_mp_fail = 1;
+ MPTCP_INC_STATS(sock_net(ssk), MPTCP_MIB_MPFAILTX);
+ }
return subflow->mp_join ? MAPPING_INVALID : MAPPING_DUMMY;
}
+ subflow->valid_csum_seen = 1;
return MAPPING_OK;
}
@@ -1099,6 +1102,18 @@ static void subflow_sched_work_if_closed
}
}
+static bool subflow_can_fallback(struct mptcp_subflow_context *subflow)
+{
+ struct mptcp_sock *msk = mptcp_sk(subflow->conn);
+
+ if (subflow->mp_join)
+ return false;
+ else if (READ_ONCE(msk->csum_enabled))
+ return !subflow->valid_csum_seen;
+ else
+ return !subflow->fully_established;
+}
+
static bool subflow_check_data_avail(struct sock *ssk)
{
struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
@@ -1176,7 +1191,7 @@ fallback:
return true;
}
- if (subflow->mp_join || subflow->fully_established) {
+ if (!subflow_can_fallback(subflow)) {
/* fatal protocol error, close the socket.
* subflow_error_report() will introduce the appropriate barriers
*/
Patches currently in stable-queue which might be from mathew.j.martineau@xxxxxxxxxxxxxxx are
queue-5.17/mptcp-do-tcp-fallback-on-early-dss-checksum-failure.patch
