net: Get rid of rtnl_link_stats64 / net_device_stats union

In commit be1f3c2c027cc5ad735df6a45a542ed1db7ec48b "net: Enable 64-bit
net device statistics on 32-bit architectures" I redefined struct
net_device_stats so that it could be used in a union with struct
rtnl_link_stats64, avoiding the need for explicit copying or
conversion between the two.  However, this is unsafe because there is
no locking required and no lock consistently held around calls to
dev_get_stats() and use of the statistics structure it returns.

In commit 28172739f0a276eb8d6ca917b3974c2edb036da3 "net: fix 64 bit
counters on 32 bit arches" Eric Dumazet dealt with that problem by
requiring callers of dev_get_stats() to provide storage for the
result.  This means that the net_device::stats64 field and the padding
in struct net_device_stats are now redundant, so remove them.

Update the comment on net_device_ops::ndo_get_stats64 to reflect its
new usage.

Change dev_txq_stats_fold() to use struct rtnl_link_stats64, since
that is what all its callers are really using and it is no longer
going to be compatible with struct net_device_stats.

Eric Dumazet suggested the separate function for the structure
conversion.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Acked-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 27 insertions, 6 deletions

diff --git a/net/8021q/vlan_dev.c b/net/8021q/vlan_dev.c
index a1b8171cfa7b..7cb285f96b99 100644
--- a/net/8021q/vlan_dev.c
+++ b/net/8021q/vlan_dev.c
@@ -805,7 +805,7 @@ static u32 vlan_ethtool_get_flags(struct net_device *dev)
 
 static struct rtnl_link_stats64 *vlan_dev_get_stats64(struct net_device *dev, struct rtnl_link_stats64 *stats)
 {
-        dev_txq_stats_fold(dev, (struct net_device_stats *)stats);
+        dev_txq_stats_fold(dev, stats);
 
         if (vlan_dev_info(dev)->vlan_rx_stats) {
                 struct vlan_rx_stats *p, accum = {0};
diff --git a/net/core/dev.c b/net/core/dev.c
index eb4201cf9c8c..79ee26ef5095 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -5274,10 +5274,10 @@ void netdev_run_todo(void)
 /**
  *      dev_txq_stats_fold - fold tx_queues stats
  *      @dev: device to get statistics from
- *      @stats: struct net_device_stats to hold results
+ *      @stats: struct rtnl_link_stats64 to hold results
  */
 void dev_txq_stats_fold(const struct net_device *dev,
-                        struct net_device_stats *stats)
+                        struct rtnl_link_stats64 *stats)
 {
         unsigned long tx_bytes = 0, tx_packets = 0, tx_dropped = 0;
         unsigned int i;
@@ -5297,6 +5297,27 @@ void dev_txq_stats_fold(const struct net_device *dev,
 }
 EXPORT_SYMBOL(dev_txq_stats_fold);
 
+/* Convert net_device_stats to rtnl_link_stats64.  They have the same
+ * fields in the same order, with only the type differing.
+ */
+static 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));
+        memcpy(stats64, netdev_stats, sizeof(*stats64));
+#else
+        size_t i, n = sizeof(*stats64) / sizeof(u64);
+        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));
+        for (i = 0; i < n; i++)
+                dst[i] = src[i];
+#endif
+}
+
 /**
  *      dev_get_stats   - get network device statistics
  *      @dev: device to get statistics from
@@ -5317,11 +5338,11 @@ const struct rtnl_link_stats64 *dev_get_stats(struct net_device *dev,
                 return ops->ndo_get_stats64(dev, storage);
         }
         if (ops->ndo_get_stats) {
-                memcpy(storage, ops->ndo_get_stats(dev), sizeof(*storage));
+                netdev_stats_to_stats64(storage, ops->ndo_get_stats(dev));
                 return storage;
         }
-        memcpy(storage, &dev->stats, sizeof(*storage));
-        dev_txq_stats_fold(dev, (struct net_device_stats *)storage);
+        netdev_stats_to_stats64(storage, &dev->stats);
+        dev_txq_stats_fold(dev, storage);
         return storage;
 }
 EXPORT_SYMBOL(dev_get_stats);