[IPV6]: multicast join and misc

Here is a simplified version of the patch to fix a bug in IPv6
multicasting. It:

1) adds existence check & EADDRINUSE error for regular joins
2) adds an exception for EADDRINUSE in the source-specific multicast
        join (where a prior join is ok)
3) adds a missing/needed read_lock on sock_mc_list; would've raced
        with destroying the socket on interface down without
4) adds a "leave group" in the (INCLUDE, empty) source filter case.
        This frees unneeded socket buffer memory, but also prevents
        an inappropriate interaction among the 8 socket options that
        mess with this. Some would fail as if in the group when you
        aren't really.

Item #4 had a locking bug in the last version of this patch; rather than
removing the idev->lock read lock only, I've simplified it to remove
all lock state in the path and treat it as a direct "leave group" call for
the (INCLUDE,empty) case it covers. Tested on an MP machine. :-)

Much thanks to HoerdtMickael <hoerdt@clarinet.u-strasbg.fr> who
reported the original bug.

Signed-off-by: David L Stevens <dlstevens@us.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 3 insertions, 2 deletions

diff --git a/net/ipv6/ipv6_sockglue.c b/net/ipv6/ipv6_sockglue.c
index 279ab86be662..f3ef4c38d315 100644
--- a/net/ipv6/ipv6_sockglue.c
+++ b/net/ipv6/ipv6_sockglue.c
@@ -423,11 +423,12 @@ done:
                         psin6 = (struct sockaddr_in6 *)&greqs.gsr_group;
                         retv = ipv6_sock_mc_join(sk, greqs.gsr_interface,
                                 &psin6->sin6_addr);
-                        if (retv)
+                        /* prior join w/ different source is ok */
+                        if (retv && retv != -EADDRINUSE)
                                 break;
                         omode = MCAST_INCLUDE;
                         add = 1;
-                } else /*IP_DROP_SOURCE_MEMBERSHIP */ {
+                } else /* MCAST_LEAVE_SOURCE_GROUP */ {
                         omode = MCAST_INCLUDE;
                         add = 0;
                 }