net/core: relax BUILD_BUG_ON in netdev_stats_to_stats64

The netdev_stats_to_stats64 function copies the deprecated
net_device_stats format stats into rtnl_link_stats64 for legacy support
purposes, but with the BUILD_BUG_ON as it was, it wasn't possible to
extend rtnl_link_stats64 without also extending net_device_stats. Relax
the BUILD_BUG_ON to only require that rtnl_link_stats64 is larger, and
zero out all the stat counters that aren't present in net_device_stats.

CC: Eric Dumazet <edumazet@google.com>
CC: netdev@vger.kernel.org
Signed-off-by: Jarod Wilson <jarod@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 13 insertions, 6 deletions

diff --git a/net/core/dev.c b/net/core/dev.c
index 8cba3d852f25..65863e512227 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -7253,24 +7253,31 @@ void netdev_run_todo(void)
         }
 }
 
-/* Convert net_device_stats to rtnl_link_stats64.  They have the same
- * fields in the same order, with only the type differing.
+/* Convert net_device_stats to rtnl_link_stats64. rtnl_link_stats64 has
+ * all the same fields in the same order as net_device_stats, with only
+ * the type differing, but rtnl_link_stats64 may have additional fields
+ * at the end for newer counters.
  */
 void netdev_stats_to_stats64(struct rtnl_link_stats64 *stats64,
                              const struct net_device_stats *netdev_stats)
 {
 #if BITS_PER_LONG == 64
-        BUILD_BUG_ON(sizeof(*stats64) != sizeof(*netdev_stats));
+        BUILD_BUG_ON(sizeof(*stats64) < sizeof(*netdev_stats));
         memcpy(stats64, netdev_stats, sizeof(*stats64));
+        /* zero out counters that only exist in rtnl_link_stats64 */
+        memset((char *)stats64 + sizeof(*netdev_stats), 0,
+               sizeof(*stats64) - sizeof(*netdev_stats));
 #else
-        size_t i, n = sizeof(*stats64) / sizeof(u64);
+        size_t i, n = sizeof(*netdev_stats) / sizeof(unsigned long);
         const unsigned long *src = (const unsigned long *)netdev_stats;
         u64 *dst = (u64 *)stats64;
 
-        BUILD_BUG_ON(sizeof(*netdev_stats) / sizeof(unsigned long) !=
-                     sizeof(*stats64) / sizeof(u64));
+        BUILD_BUG_ON(n > sizeof(*stats64) / sizeof(u64));
         for (i = 0; i < n; i++)
                 dst[i] = src[i];
+        /* zero out counters that only exist in rtnl_link_stats64 */
+        memset((char *)stats64 + n * sizeof(u64), 0,
+               sizeof(*stats64) - n * sizeof(u64));
 #endif
 }
 EXPORT_SYMBOL(netdev_stats_to_stats64);