From: Flavio Leitner <redacted>
Date: Mon, 30 Jul 2007 13:04:48 -0300

The sock_copy() function uses memcpy() to clone the socket
including the struct ip_mc_socklist *mc_list pointer.

The ip_mc_drop_socket() function is called when socket is closed
to free these objects leaving the other sockets cloned from the
same master socket with invalid pointers.

This patch sets mc_list of cloned socket to NULL.

Signed-off-by: Flavio Leitner <redacted>

Allowing non-datagram sockets to end up with a non-NULL inet->mc_list
in the first place is a bug.

Multicast subscriptions cannot even be used with TCP and DCCP, which
are the only two users of these connection oriented socket functions.

The first thing that TCP and DCCP do, in fact, for input packet
processing is drop the packet if it is not unicast.

Therefore the fix really is for the inet layer to reject multicast
subscription requests on sockets for which that absolutely does not
make sense.  There is no reason these functions in
inet_connection_sock.c should need to be mindful of multicast
state. :-)