On Wed, May 25, 2022 at 12:32:04PM +0200, Matthieu Baerts wrote: > 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! :) I have already done a release with the first change in it, sorry, but have queued this up now. Given that this is fixing a problem with that commit, I'll go do a release right now for 5.17 and 5.15. thanks, greg k-h
