Re: [Qemu-devel] [PATCH] New feature - RFC3931 L2TPv3 network transport using static Ethernet over L2TPv3 tunnels

[Stefan Hajnoczi]

On Sun, Mar 09, 2014 at 05:06:15PM +0000, Anton Ivanov wrote:
> >>+   return -1;
> >>+    }
> >>+
> >>+    freeaddrinfo(result);
> >>+
> >>+    memset(&hints, 0, sizeof(hints));
> >>+
> >>+    if (s->ipv6) {
> >>+   hints.ai_family = AF_INET6;
> >>+    } else {
> >>+   hints.ai_family = AF_INET;
> >>+    }
> >>+    if (s->udp) {
> >>+   hints.ai_socktype = SOCK_DGRAM;
> >>+   hints.ai_protocol = 0;
> >>+    } else {
> >>+   hints.ai_socktype = SOCK_RAW;
> >>+   hints.ai_protocol = IPPROTO_L2TP;
> >Hang on, this is bogus.  This is a *userspace* L2TP implementation!
> >
> >We don't want a kernel L2TP driver to handle this socket.  Luckily this
> >never happens anyway since net/l2tp/l2tp_ip.c only registers its socket
> >type for <AF_INET, SOCK_DGRAM, IPPROTO_L2TP> and <AF_INET6, SOCK_DGRAM,
> >IPPROTO_L2TP>.
> >
> >When we create this socket with <AF_INET, SOCK_RAW, IPPROTO_L2TP> what
> >really happens is that the kernel falls back to the IPv4 raw socket
> >driver due to a wildcard match.
> >
> >In other words, we shouldn't use IPPROTO_L2TP.  Just use 0.
> >
> 
> This is not passed to socket directly - both setups share a call to
> getaddinfo() after that and use whatever it returns.
> 
> If you pass family, RAW, 0 to getaddrinfo it returns  family, DGRAM,
> 0. So when you use it later on the socket is setup incorrectly.
> 
> If you pass RAW, PROTO_L2TPV3 it returns the correct values to setup
> the socket. Bug for bug canceling each other out :(

That doesn't match what I see.  Can you double-check your test and figure out
what is happening?

Here is my test:

$ grep -r SOCK_RAW /usr/include/
/usr/include/bits/socket_type.h:  SOCK_RAW = 3, /* Raw protocol interface.  */
$ ./a
src ai_family 2 ai_socketype 3 ai_protocol 0
dst ai_family 2 ai_socketype 3 ai_protocol 0
$ cat a.c
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>

int main(int argc, char **argv)
{
    int fd, gairet;
    struct addrinfo hints;
    struct addrinfo * result = NULL;

    memset(&hints, 0, sizeof(hints));
    hints.ai_family = AF_INET;
    hints.ai_socktype = SOCK_RAW;
    hints.ai_protocol = 0;

    gairet = getaddrinfo("localhost", NULL, &hints, &result);
    if ((gairet !=0) || (result == NULL)) {
        fprintf(stderr, "could not resolve src, errno = %s\n", 
gai_strerror(gairet));
        return 1;
    }

    printf("src ai_family %d ai_socketype %d ai_protocol %d\n",
           result->ai_family, result->ai_socktype, result->ai_protocol);

    freeaddrinfo(result);

    memset(&hints, 0, sizeof(hints));
    hints.ai_family = AF_INET;
    hints.ai_socktype = SOCK_RAW;
    hints.ai_protocol = 0;

    gairet = getaddrinfo("8.8.8.8", NULL, &hints, &result);
    if ((gairet !=0) || (result == NULL)) {
        fprintf(stderr, "could not resolve dst, errno = %s\n", 
gai_strerror(gairet));
        return 1;
    }

    printf("dst ai_family %d ai_socketype %d ai_protocol %d\n",
           result->ai_family, result->ai_socktype, result->ai_protocol);

    freeaddrinfo(result);

    return 0;
}