[PATCH 1/1] igmp: fix ip_mc_clear_src to not reset ip_mc_list->sf{mode,count}

[Veaceslav Falico <vfalico@redhat.com>]

ip_mc_clear_src resets the imc->sfcount and imc->sfmode, without taking into
account the current number of sockets listening on that multicast struct, which
can lead to bogus routes for local listeners.

On NETDEV_DOWN/UP event, if there were 3 multicast listeners for that interface's
address, the imc->sfcount[MCAST_EXCLUDE] will be reset to 1. And after that a
listener socket destroys, multicast traffic will not be delivered to local
listeners because __mkroute_output drops the local flag for the route (by
checking ip_check_mc).

Signed-off-by: Veaceslav Falico <vfalico@redhat.com>

diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c
index 1fd3d9c..b14f371 100644
--- a/net/ipv4/igmp.c
+++ b/net/ipv4/igmp.c
@@ -1775,9 +1775,6 @@ static void ip_mc_clear_src(struct ip_mc_list *pmc)
 		kfree(psf);
 	}
 	pmc->sources = NULL;
-	pmc->sfmode = MCAST_EXCLUDE;
-	pmc->sfcount[MCAST_INCLUDE] = 0;
-	pmc->sfcount[MCAST_EXCLUDE] = 1;
 }