Re: [PATCH 7/8] SUNRPC: Set V6ONLY socket option for RPC listener sockets

["Chuck Lever" <chuck.lever@oracle.com>]

On Fri, Jul 18, 2008 at 9:05 PM, J. Bruce Fields <bfields@fieldses.org> wrote:
> On Mon, Jun 30, 2008 at 06:46:17PM -0400, Chuck Lever wrote:
>> My plan is to use an AF_INET listener on systems that support only IPv4,
>> and an AF_INET6 listener on systems that can support IPv6. Incoming
>> IPv4 packets will be posted to an AF_INET6 listener with a mapped IPv4
>> address.
>>
>> Max Matveev <makc@sgi.com> says:
>>   Creating a single listener can be dangerous - if net.ipv6.bindv6only
>>   is enabled then it's possible to create another listener in v4
>>   namespace on the same port and steal the traffic from the "unifed"
>>   listener. You need to disable V6ONLY explicitly via a sockopt to stop
>>   that.
>
> Is the V6ONLY option documented anywhere?  A quick grep through the
> kernel sources and a couple man pages didn't turn up anything.

I didn't find anything that documented it, so I based this patch on
studying pieces of the IPv6 code that use this flag.  It would be
worth passing this patch by netdev.

>>
>> Set appropriate socket option on RPC server listener sockets to prevent
>> this.
>>
>> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
>> ---
>>
>>  net/sunrpc/svcsock.c |   12 ++++++++++++
>>  1 files changed, 12 insertions(+), 0 deletions(-)
>>
>>
>> diff --git a/net/sunrpc/svcsock.c b/net/sunrpc/svcsock.c
>> index 3e65719..43c21f7 100644
>> --- a/net/sunrpc/svcsock.c
>> +++ b/net/sunrpc/svcsock.c
>> @@ -1114,6 +1114,7 @@ static struct svc_sock *svc_setup_socket(struct svc_serv *serv,
>>       struct svc_sock *svsk;
>>       struct sock     *inet;
>>       int             pmap_register = !(flags & SVC_SOCK_ANONYMOUS);
>> +     int zero        = 0;
>>
>>       dprintk("svc: svc_setup_socket %p\n", sock);
>>       if (!(svsk = kzalloc(sizeof(*svsk), GFP_KERNEL))) {
>> @@ -1146,6 +1147,17 @@ static struct svc_sock *svc_setup_socket(struct svc_serv *serv,
>>       else
>>               svc_tcp_init(svsk, serv);
>>
>> +     /*
>> +      * We start one listener per sv_serv.  We want AF_INET
>> +      * requests to be automatically shunted to our AF_INET6
>> +      * listener using a mapped IPv4 address.  Make sure
>> +      * no-one starts an equivalent IPv4 listener, which
>> +      * would steal our incoming connections.
>> +      */
>> +     if (serv->sv_family == AF_INET6)
>> +             kernel_setsockopt(sock, SOL_IPV6, IPV6_V6ONLY,
>> +                                     (char *)&zero, sizeof(zero));
>> +
>>       dprintk("svc: svc_setup_socket created %p (inet %p)\n",
>>                               svsk, svsk->sk_sk);
>>
>>
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