net: tipc: prepare attrs in __tipc_nl_compat_dumpit()

__tipc_nl_compat_dumpit() calls tipc_nl_publ_dump() which expects
the attrs to be available by genl_dumpit_info(cb)->attrs. Add info
struct and attr parsing in compat dumpit function.

Reported-by: syzbot+8d37c50ffb0f52941a5e@syzkaller.appspotmail.com
Fixes: 057af707 ("net: tipc: have genetlink code to parse the attrs during dumpit")
Signed-off-by: NJiri Pirko <jiri@mellanox.com>
Acked-by: NJon Maloy <jon.maloy@ericsson.com>
Signed-off-by: NJakub Kicinski <jakub.kicinski@netronome.com>

net/tipc/netlink_compat.c

@@ -181,6 +181,7 @@ static int __tipc_nl_compat_dumpit(struct tipc_nl_compat_cmd_dump *cmd,
 				   struct tipc_nl_compat_msg *msg,
 				   struct sk_buff *arg)
 {
+	struct genl_dumpit_info info;
 	int len = 0;
 	int err;
 	struct sk_buff *buf;
@@ -191,6 +192,7 @@ static int __tipc_nl_compat_dumpit(struct tipc_nl_compat_cmd_dump *cmd,
 	memset(&cb, 0, sizeof(cb));
 	cb.nlh = (struct nlmsghdr *)arg->data;
 	cb.skb = arg;
+	cb.data = &info;
 
 	buf = nlmsg_new(NLMSG_GOODSIZE, GFP_KERNEL);
 	if (!buf)
@@ -209,6 +211,13 @@ static int __tipc_nl_compat_dumpit(struct tipc_nl_compat_cmd_dump *cmd,
 		goto err_out;
 	}
 
+	info.attrs = attrbuf;
+	err = nlmsg_parse_deprecated(cb.nlh, GENL_HDRLEN, attrbuf,
+				     tipc_genl_family.maxattr,
+				     tipc_genl_family.policy, NULL);
+	if (err)
+		goto err_out;
+
 	do {
 		int rem;