tipc: purge deferredq list for each grp member in tipc_group_delete

Syzbot reported a memleak caused by grp members' deferredq list not
purged when the grp is be deleted.

The issue occurs when more(msg_grp_bc_seqno(hdr), m->bc_rcv_nxt) in
tipc_group_filter_msg() and the skb will stay in deferredq.

So fix it by calling __skb_queue_purge for each member's deferredq
in tipc_group_delete() when a tipc sk leaves the grp.

Fixes: b87a5ea31c93 ("tipc: guarantee group unicast doesn't bypass group broadcast")
Reported-by: [e-mail]
Signed-off-by: Xin Long <[e-mail]>
Acked-by: Ying Xue <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/tipc/group.c

···
 
 	rbtree_postorder_for_each_entry_safe(m, tmp, tree, tree_node) {
 		tipc_group_proto_xmit(grp, m, GRP_LEAVE_MSG, &xmitq);
+		__skb_queue_purge(&m->deferredq);
 		list_del(&m->list);
 		kfree(m);
 	}