ipvs: Restrict sync message to 255 connections

The nr_conns variable in the sync message header is only eight bits wide
and will overflow on interfaces with a large MTU. As a result the backup
won't parse all connections contained in the sync buffer. On regular
ethernet with an MTU of 1500 this isn't a problem, because we can't
overflow the value, but consider jumbo frames being used on a cross-over
connection between both directors.

We now restrict the size of the sync buffer, so that we never put more
than 255 connections into a single sync buffer.

Signed-off-by: Sven Wegener <sven.wegener@stealer.net>
Signed-off-by: Simon Horman <horms@verge.net.au>

1 files changed, 4 insertions, 2 deletions

diff --git a/net/ipv4/ipvs/ip_vs_sync.c b/net/ipv4/ipvs/ip_vs_sync.c
index 28237a5f62e..de5e7e118ee 100644
--- a/net/ipv4/ipvs/ip_vs_sync.c
+++ b/net/ipv4/ipvs/ip_vs_sync.c
@@ -30,6 +30,7 @@
 #include <linux/err.h>
 #include <linux/kthread.h>
 #include <linux/wait.h>
+#include <linux/kernel.h>
 
 #include <net/ip.h>
 #include <net/sock.h>
@@ -99,6 +100,7 @@ struct ip_vs_sync_thread_data {
 */
 
 #define SYNC_MESG_HEADER_LEN    4
+#define MAX_CONNS_PER_SYNCBUFF  255 /* nr_conns in ip_vs_sync_mesg is 8 bit */
 
 struct ip_vs_sync_mesg {
         __u8                    nr_conns;
@@ -516,8 +518,8 @@ static int set_sync_mesg_maxlen(int sync_state)
                 num = (dev->mtu - sizeof(struct iphdr) -
                        sizeof(struct udphdr) -
                        SYNC_MESG_HEADER_LEN - 20) / SIMPLE_CONN_SIZE;
-                sync_send_mesg_maxlen =
-                        SYNC_MESG_HEADER_LEN + SIMPLE_CONN_SIZE * num;
+                sync_send_mesg_maxlen = SYNC_MESG_HEADER_LEN +
+                        SIMPLE_CONN_SIZE * min(num, MAX_CONNS_PER_SYNCBUFF);
                 IP_VS_DBG(7, "setting the maximum length of sync sending "
                           "message %d.\n", sync_send_mesg_maxlen);
         } else if (sync_state == IP_VS_STATE_BACKUP) {