please see https://github.com/openssl/openssl/pull/5024
mattcaswell asks on github: mattcaswell> I am unclear about the underlying premise of this PR: mcr> This patch refactors the DTLSv1_listen() to create an mcr> alternative API that is called DTLSv1_accept(). mcr> DTLSv1_accept() is useable by programs that need to treat mcr> DTLS interfaces in a way similar to TCP: new connections mcr> must be accepted, and new sockets created. mattcaswell> Your going to give more justification than this. Why is it mattcaswell> that DTLSv1_listen() is not appropriate for your use case? As I understand using DTLSv1_listen(), one does the following: 1) open a UDP socket, bind(2) it appropriately. {in an RTP context, one might already know the remote port numbers, and one could connect(2) it already. In the CoAP case, that certainly is not the case} Put the socket into an SSL, do appropriate blocking or non-blocking event handling in application. 2) call DTLSv1_listen() when there is traffic. DTLSv1_listen() will process (via peek) the first packet in the socket. If it's a Client Hello without a cookie, then a Hello Verify is sent back (%). If it ate the packet, then it loops until it find something it can't handle or runs out of packets. 3) DTLSv1_listen(), when it finds a Client Hello with a cookie, marks the provided SSL as having transitioned to a state where things can start, and it returns 1, along with the BIO_ADDR of the newly Verify Hello'ed client. 4) the application is now expected to connect() the FD to the BIO_ADDR, and call SSL_accept(), and then to proceed with SSL_read()/SSL_write(), etc. Perhaps I've gotten something wrong with this process. This flow is entirely appropriate for a RTP user, but for a CoAP server there are a number of problems: a) when the existing FD is connect(2) any future traffic to the bound port will get rejected with no port. So the application really has to open a new socket first. The application can do this two ways: it can open a new socket on which to receive new connections, or it can open a new socket on which to communicate with the new client. The second method is better for reason (b) below. Either way, it socket to communicate with the client needs to be bind(2) to the address that the client used to communicate with the server, and DTLSv1_listen() didn't collect or return that information. b) the existing FD might have additional packets from other clients. This argues for opening a new socket for the new client, and leaving the queue on the existing FD. c) the DTLSv1_listen() uses the SSL* (and associated CTX) that is provided to it for callbacks, and cookie verification. It modifies the state of that SSL* to continue the transaction. I think that the roles should be split up. also, from point (2) above: (%) - the send that DTLSv1_listen() depends upon the socket having been bind(2) with a non-INADDR_ANY/IN6ADDR_ANY_INIT IP address, or that the system in question has only a single IP address. This is because the write that is done relies upon the kernel to pick the right source address, which appears to be easy for IPv4 with a single interface, but trivially can fail for IPv6 even with a single interface due to temporary, stable-private, and link-local addresses. DTLSv1_accept() takes two SSL*. The first is used for cookie verification, while the second is filled in with a new FD that has been bind/connect to the client and state advanced to be ready for SSL_accept(). It also returns the same BIO_ADDR for the client, but that could be removed as it can trivially be retrieved from the new SSL*. mattcaswell> In any case the PR as it currently stands is a very long way mattcaswell> off being acceptable: I totally agree, but I had to post something to start the conversation. mattcaswell> * As you point out the use of the POSIX socket APIs is mattcaswell> unacceptable and is at the wrong level of abstraction. I mattcaswell> might perhaps expect to see this sort of thing in the BIO mattcaswell> layer. a) I could move the socket creation code into BIO layer, a new BIO_ctrl method could be created to "duplicate" the BIO. This would probably eliminate having to expose BIO_ADDR_sockaddr{,_size} from libcrypto->libssl. b) creation of a new socket could be a new callback. c) DTLSv1_accept() could return at: "now set up a socket based upon the original rbio's peer/addr" as all of the subsequent operations could be done by the application given BIO_dgram_get_peer(rbio, client) and BIO_dgram_get_addr(rbio, ouraddr) d) a combination of (a) and (c), where the duplication code is provided by the BIO layer, but the application could do something different if it needed to. My preference is for (d), because I think that it's common code and the application writer will get it wrong. In particular, you need to open the socket with SO_REUSEPORT in order to be allowed to bind() the new socket before connect(2)ing it. If there were a system call to do both at the same time it would be better. There is a race condition by calling bind() first, because the kernel is likely to put new traffic from new sources into the new socket. They will be dropped as having the wrong cookies. mattcaswell> * The code does not seem to be portable - it needs mattcaswell> to work on all our platforms mattcaswell> * There is no documentation I will write more documentation when I am sure what the structure is going to be. mattcaswell> I noticed a number of other things at a more specific level, mattcaswell> just scanning through the code, but at this point I have not mattcaswell> reviewed it in detail. I am not yet convinced there is a mattcaswell> need for this. I absolutely need to have recvmsg()/sendmsg() in the bss_dgram.c in order to get the destination address used. This IPv6 code is portable, since the RFC API says how to do it. The IPv4 code varies by OS; I can probably write the correct thing and get tested it on FreeBSD, but I have no idea about Windows. We used to solve this by opening a socket for each interface and listening to the routing socket, or having a human configure an explicit list of interfaces, or just failing on multi-homed hosts. I propose to split this pull request up into one that deals with the changes to the BIO layer only. A second pull request will include the "duplicate" BIO functionality. A third then deals with the d1_lib.c layer. -- ] Never tell me the odds! | ipv6 mesh networks [ ] Michael Richardson, Sandelman Software Works | network architect [ ] m...@sandelman.ca http://www.sandelman.ca/ | ruby on rails [ -- openssl-dev mailing list To unsubscribe: https://mta.openssl.org/mailman/listinfo/openssl-dev