On Wed, May 23, 2018 at 03:04:53PM +0800, Xin Long wrote: > On Tue, May 22, 2018 at 7:51 PM, Neil Horman <nhorman@xxxxxxxxxxxxx> wrote: > > On Tue, May 22, 2018 at 03:07:57PM +0800, Xin Long wrote: > >> On Mon, May 21, 2018 at 9:48 PM, Neil Horman <nhorman@xxxxxxxxxxxxx> wrote: > >> > On Mon, May 21, 2018 at 02:16:56PM +0200, Michael Tuexen wrote: > >> >> > On 21. May 2018, at 13:39, Neil Horman <nhorman@xxxxxxxxxxxxx> wrote: > >> >> > > >> >> > On Sun, May 20, 2018 at 10:54:04PM -0300, Marcelo Ricardo Leitner wrote: > >> >> >> On Sun, May 20, 2018 at 08:50:59PM -0400, Neil Horman wrote: > >> >> >>> On Sat, May 19, 2018 at 03:44:40PM +0800, Xin Long wrote: > >> >> >>>> This feature is actually already supported by sk->sk_reuse which can be > >> >> >>>> set by SO_REUSEADDR. But it's not working exactly as RFC6458 demands in > >> >> >>>> section 8.1.27, like: > >> >> >>>> > >> >> >>>> - This option only supports one-to-one style SCTP sockets > >> >> >>>> - This socket option must not be used after calling bind() > >> >> >>>> or sctp_bindx(). > >> >> >>>> > >> >> >>>> Besides, SCTP_REUSE_PORT sockopt should be provided for user's programs. > >> >> >>>> Otherwise, the programs with SCTP_REUSE_PORT from other systems will not > >> >> >>>> work in linux. > >> >> >>>> > >> >> >>>> This patch reuses sk->sk_reuse and works pretty much as SO_REUSEADDR, > >> >> >>>> just with some extra setup limitations that are neeeded when it is being > >> >> >>>> enabled. > >> >> >>>> > >> >> >>>> "It should be noted that the behavior of the socket-level socket option > >> >> >>>> to reuse ports and/or addresses for SCTP sockets is unspecified", so it > >> >> >>>> leaves SO_REUSEADDR as is for the compatibility. > >> >> >>>> > >> >> >>>> Signed-off-by: Xin Long <lucien.xin@xxxxxxxxx> > >> >> >>>> --- > >> >> >>>> include/uapi/linux/sctp.h | 1 + > >> >> >>>> net/sctp/socket.c | 48 +++++++++++++++++++++++++++++++++++++++++++++++ > >> >> >>>> 2 files changed, 49 insertions(+) > >> >> >>>> > >> >> >>> A few things: > >> >> >>> > >> >> >>> 1) I agree with Tom, this feature is a complete duplication of the SK_REUSEPORT > >> >> >>> socket option. I understand that this is an implementation of the option in the > >> >> >>> RFC, but its definately a duplication of a feature, which makes several things > >> >> >>> really messy. > >> >> >>> > >> >> >>> 2) The overloading of the sk_reuse opeion is a bad idea, for several reasons. > >> >> >>> Chief among them is the behavioral interference between this patch and the > >> >> >>> SO_REUSEADDR socket level option, that also sets this feature. If you set > >> >> >>> sk_reuse via SO_REUSEADDR, you will set the SCTP port reuse feature regardless > >> >> >>> of the bind or 1:1/1:m state of the socket. Vice versa, if you set this socket > >> >> >>> option via the SCTP_PORT_REUSE option you will inadvertently turn on address > >> >> >>> reuse for the socket. We can't do that. > >> >> >> > >> >> >> Given your comments, going a bit further here, one other big > >> >> >> implication is that a port would never be able to be considered to > >> >> >> fully meet SCTP standards regarding reuse because a rogue application > >> >> >> may always abuse of the socket level opt to gain access to the port. > >> >> >> > >> >> >> IOW, the patch allows the application to use such restrictions against > >> >> >> itself and nothing else, which undermines the patch idea. > >> >> >> > >> >> > Agreed. > >> >> > > >> >> >> I lack the knowledge on why the SCTP option was proposed in the RFC. I > >> >> >> guess they had a good reason to add the restriction on 1:1/1:m style. > >> >> >> Does the usage of the current imply in any risk to SCTP sockets? If > >> >> >> yes, that would give some grounds for going forward with the SCTP > >> >> >> option. > >> >> >> > >> >> > I'm also not privy to why the sctp option was proposed, though I expect that the > >> >> > lack of standardization of SO_REUSEPORT probably had something to do with it. > >> >> > As for the reasoning behind restriction to only 1:1 sockets, if I had to guess, > >> >> > I would say it likely because it creates ordering difficulty at the application > >> >> > level. > >> >> > > >> >> > CC-ing Michael Tuxen, who I believe had some input on this RFC. Hopefully he > >> >> > can shed some light on this. > >> >> Dear all, > >> >> > >> >> the reason this was added is to have a specified way to allow a system to > >> >> behave like a client and server making use of the INIT collision. > >> >> > >> >> For 1-to-many style sockets you can do this by creating a socket, binding it, > >> >> calling listen on it and trying to connect to the peer. > >> >> > >> >> For 1-to-1 style sockets you need two sockets for it. One listener and one > >> >> you use to connect (and close it in case of failure, open a new one...). > >> >> > >> >> It was not clear if one can achieve this with SO_REUSEPORT and/or SO_REUSEADDR > >> >> on all platforms. We left that unspecified. > >> >> > >> >> I hope this makes the intention clearer. > >> >> > >> > I think it makes the intention clearer yes, but it unfortunately does nothing in > >> > my mind to clarify how the implementation should best handle the potential > >> > overlap in functionality. What I see here is that we have two functional paths > >> > (the SO_REUSEPORT path and the SCTP_PORT_REUSE path), which may or may not > >> > (depending on the OS implementation achieve the same functional goal (allowing > >> > multiple sockets to share a port while allowing one socket to listen and the > >> > other connect to a remote peer). If both implementations do the same thing on a > >> > given platform, we can either just alias one to another and be done, but if they > >> > don't then we either have to implement both paths, and ensure that the > >> > SO_REUSEPORT path is a no-op/error return for SCTP sockets, or that each path > >> > implements a distinct feature set that is cleaarly documented. > >> > > >> > That said, I think we may be in luck. Looking at the connect and listen paths, > >> > it appears to me that: > >> > > >> > 1) Sockets ignore SO_REUSEPORT in the connect and listen paths (save for any > >> > autobinding) so it would appear that the intent of the SCTP rfc can be honored > >> > via SO_REUSEPORT on linux. > >> > > >> > 2) SO_REUSEPORT prevents changing state after a bind has occured, so we can honr > >> > that part of the SCTP RFC. > >> > > >> > The only missing part is the restriction that SCTP_REUSE_PORT has which is > >> > unaccounted for is that 1:M sockets aren't allowed to enable port reuse. > >> > However, I think the implication from Michaels description above is that port > >> > reuse on a 1:M socket is implicit because a single socket can connect and listen > >> > in that use case, rather than there being a danger to doing so. > >> > > >> > As such, I would propose that we implement this socket option by simply setting > >> > the sk->sk_reuseport field in the sock structure, and document the fact that > >> > linux does not restrict port reuse from 1:M sockets. > >> Note that, sk->sk_reuseport is not affecting linux SCTP socket at all now. > >> linux SCTP socket doesn't really have SO_REUSEADDR (sk->sk_reuse) > >> support, but use sk->sk_reuse as REUSE_PORT, (yes, it is confusing). > >> Pls refer to sctp_get_port_local(). > >> > > No, its not used now, but if you do use it to do something specific to SCTP (via > > the SCTP_REUSE_PORT socket option), you risk aliasing SO_REUSEPORT behavior to > > it, and if it doesn't match what the RFC behavior mandates, thats a problem. > > > >> So I'm not sure using sk->sk_reuseport here means we will drop sk->sk_reuse > >> use in linux SCTP but use sk->sk_reuseport instead, or we will think that socket > >> enables 'port reuse' when either of them is set. > >> > > I don't think we would drop the behavior of sk_reuse here, why would we? As far > > as I can see, the behavior of SO_REUSEADDR (not SO_REUSEPORT), isn't in > > question, is it? > > > >> Note some users may be already using SO_REUSEADDR to enable the 'port > >> reuse' in linux sctp socket. If we're changing to sk->sk_reuseport, we may face > >> a compatibility problem. > >> > > I don't see how the behavior of SO_REUSEADDR is in question here. All I'm > > suggesting is that you simplify this patch so that the SCTP_REUSE_PORT socket > > option set sk_reuseport, as that option to my eyes conforms to the sctp rfc > > requirements. Or am I' missing something? > No, I am :) > sk_reuseport seems more complicated than sk_reuse. I kind of mixed them. > I need to check more beofore continuing. Thanks. > Thank you! Neil > > > > Neil > > > >> > >> > > >> > Thoughts? > >> > Neil > >> > > >> > -- To unsubscribe from this list: send the line "unsubscribe linux-sctp" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
