On Tue, May 24, 2022 at 11:10:41AM -0700, Mat Martineau wrote:
[ Upstream commit ae66fb2ba6c3dcaf8b9612b65aa949a1a4bed150 ]
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.
Cc: stable@vger.kernel.org # 5.17.x Cc: stable@vger.kernel.org # 5.15.x Fixes: dd8bcd1768ff ("mptcp: validate the data checksum") Acked-by: Paolo Abeni pabeni@redhat.com Signed-off-by: Mat Martineau mathew.j.martineau@linux.intel.com Signed-off-by: David S. Miller davem@davemloft.net [mathew.j.martineau: backport: Resolved bitfield conflict in protocol.h] Signed-off-by: Mat Martineau mathew.j.martineau@linux.intel.com
This patch is already in 5.17.10-rc1 and 5.15.42-rc1, but involves a context dependency on upstream commit 4cf86ae84c71 which I have requested to be dropped from the stable queues.
I'm posting this backport without the protocol.h conflict to (hopefully?) make it easier for the stable maintainers to drop 4cf86ae84c71.
For context see https://lore.kernel.org/stable/fa953ec-288f-7715-c6fb-47a222e85270@linux.int...
THanks, will take this after this round of releases.
greg k-h