Hi Greg, Mat, On 25/05/2022 09:51, Greg KH wrote: > 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@xxxxxxxxxxxxxxx> # 5.17.x >> Cc: <stable@xxxxxxxxxxxxxxx> # 5.15.x >> 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> >> --- >> >> 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@xxxxxxxxxxxxxxx/ > > THanks, will take this after this round of releases. It might already be too late but is it possible to have this patch ("mptcp: Do TCP fallback on early DSS checksum failure") and "mptcp: fix checksum byte order" in the same stable release? Note that "mptcp: fix checksum byte order" patch has been recently queued by Sasha at the same time as "mptcp: Do TCP fallback on early DSS checksum failure". A bit of context: "mptcp: fix checksum byte order" fixes an important encoding issue but it also breaks the interoperability with previous Linux versions not having this patch. The patch from Mat ("mptcp: Do TCP fallback on early DSS checksum failure") improves the situation when there is this interoperability issue with a previous Linux versions not implementing the RFC properly. The improvement is there to make the MPTCP connections falling back to TCP instead of resetting them: at least there is a connection. In other words, that would be really nice to have these two commits backported together. If it is easier, it looks best to me to delay the main fix ("mptcp: fix checksum byte order") than having the two patches in different stable versions. But I understand it was not clear and maybe too late to do these modifications. Anyway, thank you for your work maintaining these stable versions! :) Cheers, Matt -- Tessares | Belgium | Hybrid Access Solutions www.tessares.net
