ipvs: Use network byte order for sync message size

struct ip_vs_sync_mesg and ip_vs_sync_mesg_v0 are both sent across the wire
and used internally to store IPVS synchronisation messages.

Up until now the scheme used has been to convert the size field
to network byte order before sending a message on the wire and
convert it to host byte order when sending a message.

This patch changes that scheme to always treat the field
as being network byte order. This seems appropriate as
the structure is sent across the wire. And by consistently
treating the field has network byte order it is now possible
to take advantage of sparse to flag any future miss-use.

Acked-by: Julian Anastasov <ja@ssi.bg>
Acked-by: Hans Schillstrom <hans@schillstrom.com>
Signed-off-by: Simon Horman <horms@verge.net.au>

net/netfilter/ipvs/ip_vs_sync.c

@@ -246,7 +246,7 @@ struct ip_vs_sync_thread_data {
 struct ip_vs_sync_mesg_v0 {
 	__u8                    nr_conns;
 	__u8                    syncid;
-	__u16                   size;
+	__be16                  size;
 
 	/* ip_vs_sync_conn entries start here */
 };
@@ -255,7 +255,7 @@ struct ip_vs_sync_mesg_v0 {
 struct ip_vs_sync_mesg {
 	__u8			reserved;	/* must be zero */
 	__u8			syncid;
-	__u16			size;
+	__be16			size;
 	__u8			nr_conns;
 	__s8			version;	/* SYNC_PROTO_VER  */
 	__u16			spare;
@@ -335,7 +335,7 @@ ip_vs_sync_buff_create(struct netns_ipvs *ipvs)
 	sb->mesg->reserved = 0;  /* old nr_conns i.e. must be zero now */
 	sb->mesg->version = SYNC_PROTO_VER;
 	sb->mesg->syncid = ipvs->master_syncid;
-	sb->mesg->size = sizeof(struct ip_vs_sync_mesg);
+	sb->mesg->size = htons(sizeof(struct ip_vs_sync_mesg));
 	sb->mesg->nr_conns = 0;
 	sb->mesg->spare = 0;
 	sb->head = (unsigned char *)sb->mesg + sizeof(struct ip_vs_sync_mesg);
@@ -418,7 +418,7 @@ ip_vs_sync_buff_create_v0(struct netns_ipvs *ipvs)
 	mesg = (struct ip_vs_sync_mesg_v0 *)sb->mesg;
 	mesg->nr_conns = 0;
 	mesg->syncid = ipvs->master_syncid;
-	mesg->size = sizeof(struct ip_vs_sync_mesg_v0);
+	mesg->size = htons(sizeof(struct ip_vs_sync_mesg_v0));
 	sb->head = (unsigned char *)mesg + sizeof(struct ip_vs_sync_mesg_v0);
 	sb->end = (unsigned char *)mesg + ipvs->send_mesg_maxlen;
 	sb->firstuse = jiffies;
@@ -582,7 +582,7 @@ static void ip_vs_sync_conn_v0(struct net *net, struct ip_vs_conn *cp,
 	}
 
 	m->nr_conns++;
-	m->size += len;
+	m->size = htons(ntohs(m->size) + len);
 	buff->head += len;
 
 	/* check if there is a space for next one */
@@ -693,7 +693,7 @@ sloop:
 
 	p = buff->head;
 	buff->head += pad + len;
-	m->size += pad + len;
+	m->size = htons(ntohs(m->size) + pad + len);
 	/* Add ev. padding from prev. sync_conn */
 	while (pad--)
 		*(p++) = 0;
@@ -1175,10 +1175,8 @@ static void ip_vs_process_message(struct net *net, __u8 *buffer,
 		IP_VS_DBG(2, "BACKUP, message header too short\n");
 		return;
 	}
-	/* Convert size back to host byte order */
-	m2->size = ntohs(m2->size);
 
-	if (buflen != m2->size) {
+	if (buflen != ntohs(m2->size)) {
 		IP_VS_DBG(2, "BACKUP, bogus message size\n");
 		return;
 	}
@@ -1544,10 +1542,7 @@ ip_vs_send_sync_msg(struct socket *sock, struct ip_vs_sync_mesg *msg)
 	int msize;
 	int ret;
 
-	msize = msg->size;
-
-	/* Put size in network byte order */
-	msg->size = htons(msg->size);
+	msize = ntohs(msg->size);
 
 	ret = ip_vs_send_async(sock, (char *)msg, msize);
 	if (ret >= 0 || ret == -EAGAIN)