ctdb: Initialize addr struct to zero before reparsing as IPV4

Failed to kill the tcp connection that using IPv4-mapped IPv6 address
(e.g. ctdb_killtcp eth0 ::ffff:192.168.200.44:2049
::ffff:192.168.200.45:863).

When the ctdb_killtcp is used to kill the tcp connection, the IPs and
ports in the connection will be parsed to conn.client and conn.server
(call stack: main->ctdb_sock_addr_from_string->ip_from_string). In
the ip_from_string, as we are using IPv4-mapped IPv6 addresses, the
ipv6_from_string will be used to parse ip to addr.ip6 first. The next
step the ipv4_from_string will be used to reparse ip to addr.ip.

As a result, the data that dump from conn.server is "2 0 8 1 192 168
200 44 0 0 0 0 0 0 0 0 0 0 255 255 192 168 200 44 0 0 0 0", the data
from conn.client is "2 0 3 95 192 168 200 45 0 0 0 0 0 0 0 0 0 0 255 255
192 168 200 45 0 0 0 0". The connection will be add to conn_list by
ctdb_connection_list_add. Then the reset_connections_send uses conn_list
as parameter to start to reset connections in the conn_list.

In the reset_connections_send, the database "connections" will be
created. The connections from conn_list will be written to the
database(call db_hash_add), and use the data that dump from conn_client
and conn_server as key.

In the reset_connections_capture_tcp_handler, the
ctdb_sys_read_tcp_packet will receive data on the raw socket. And
extract the IPs and ports from the tcp packet. when extracting IP and
port, the tcp4_extract OR tcp6_extract will be used. Then we got the
new conn.client and conn.server. the data that dump from the
conn.server is "2 0 8 1 192 168 200 44 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0", the data from conn.client is "2 0 3 95 192 168 200 45 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0". Finally, we use the data as key to check
if this connection is one being reset(call db_hash_delete). The
db_hash_delete will return ENOENT. Because the two key that being used
by db_hash_delete and db_hash_add are different.

So, the TCP RST will be NOT sent for the connection forever. We should
initialize addr struct to zero before reparsing as IPV4 in the
ip_from_string.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=13839

Signed-off-by: Zhu Shangzhong <zhu.shangzhong@zte.com.cn>
Reviewed-by: Martin Schwenke <martin@meltin.net>
Reviewed-by: Amitay Isaacs <amitay@samba.org>

ctdb/protocol/protocol_util.c

@@ -252,6 +252,9 @@ static int ip_from_string(const char *str, ctdb_sock_addr *addr)
 		if (memcmp(&addr->ip6.sin6_addr.s6_addr[0],
 			   ipv4_mapped_prefix,
 			   sizeof(ipv4_mapped_prefix)) == 0) {
+                        /* Initialize addr struct to zero before reparsing as IPV4 */
+                        ZERO_STRUCTP(addr);
+
 			/* Reparse as IPv4 */
 			ret = ipv4_from_string(p+1, &addr->ip);
 		}