Almost all igmp functions accessing inet->mc_list are protected by
rtnl_lock(), but there is one exception which is ip_mc_sf_allow(),
so there is a chance of either ip_mc_drop_socket or ip_mc_leave_group
remove an entry while ip_mc_sf_allow is running causing a crash.
Signed-off-by: NFlavio Leitner <fleitner@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>