net: fix 64 bit counters on 32 bit arches

There is a small possibility that a reader gets incorrect values on 32
bit arches. SNMP applications could catch incorrect counters when a
32bit high part is changed by another stats consumer/provider.

One way to solve this is to add a rtnl_link_stats64 param to all
ndo_get_stats64() methods, and also add such a parameter to
dev_get_stats().

Rule is that we are not allowed to use dev->stats64 as a temporary
storage for 64bit stats, but a caller provided area (usually on stack)

Old drivers (only providing get_stats() method) need no changes.

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

3 files changed, 21 insertions, 11 deletions

diff --git a/net/core/dev.c b/net/core/dev.c
index 93b8929fa21d..92482d7a87a9 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3703,7 +3703,8 @@ void dev_seq_stop(struct seq_file *seq, void *v)
 
 static void dev_seq_printf_stats(struct seq_file *seq, struct net_device *dev)
 {
-        const struct rtnl_link_stats64 *stats = dev_get_stats(dev);
+        struct rtnl_link_stats64 temp;
+        const struct rtnl_link_stats64 *stats = dev_get_stats(dev, &temp);
 
         seq_printf(seq, "%6s: %7llu %7llu %4llu %4llu %4llu %5llu %10llu %9llu "
                    "%8llu %7llu %4llu %4llu %4llu %5llu %7llu %10llu\n",
@@ -5281,23 +5282,29 @@ EXPORT_SYMBOL(dev_txq_stats_fold);
 /**
  *      dev_get_stats   - get network device statistics
  *      @dev: device to get statistics from
+ *      @storage: place to store stats
  *
  *      Get network statistics from device. The device driver may provide
  *      its own method by setting dev->netdev_ops->get_stats64 or
  *      dev->netdev_ops->get_stats; otherwise the internal statistics
  *      structure is used.
  */
-const struct rtnl_link_stats64 *dev_get_stats(struct net_device *dev)
+const struct rtnl_link_stats64 *dev_get_stats(struct net_device *dev,
+                                              struct rtnl_link_stats64 *storage)
 {
         const struct net_device_ops *ops = dev->netdev_ops;
 
-        if (ops->ndo_get_stats64)
-                return ops->ndo_get_stats64(dev);
-        if (ops->ndo_get_stats)
-                return (struct rtnl_link_stats64 *)ops->ndo_get_stats(dev);
-
-        dev_txq_stats_fold(dev, &dev->stats);
-        return &dev->stats64;
+        if (ops->ndo_get_stats64) {
+                memset(storage, 0, sizeof(*storage));
+                return ops->ndo_get_stats64(dev, storage);
+        }
+        if (ops->ndo_get_stats) {
+                memcpy(storage, ops->ndo_get_stats(dev), sizeof(*storage));
+                return storage;
+        }
+        memcpy(storage, &dev->stats, sizeof(*storage));
+        dev_txq_stats_fold(dev, (struct net_device_stats *)storage);
+        return storage;
 }
 EXPORT_SYMBOL(dev_get_stats);
 
diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index ea3bb4c3b87d..914f42b0f039 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -330,7 +330,9 @@ static ssize_t netstat_show(const struct device *d,
 
         read_lock(&dev_base_lock);
         if (dev_isalive(dev)) {
-                const struct rtnl_link_stats64 *stats = dev_get_stats(dev);
+                struct rtnl_link_stats64 temp;
+                const struct rtnl_link_stats64 *stats = dev_get_stats(dev, &temp);
+
                 ret = sprintf(buf, fmt_u64, *(u64 *)(((u8 *) stats) + offset));
         }
         read_unlock(&dev_base_lock);
diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index e645778e9b7e..5e773ea2201d 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -791,6 +791,7 @@ static int rtnl_fill_ifinfo(struct sk_buff *skb, struct net_device *dev,
 {
         struct ifinfomsg *ifm;
         struct nlmsghdr *nlh;
+        struct rtnl_link_stats64 temp;
         const struct rtnl_link_stats64 *stats;
         struct nlattr *attr;
 
@@ -847,7 +848,7 @@ static int rtnl_fill_ifinfo(struct sk_buff *skb, struct net_device *dev,
         if (attr == NULL)
                 goto nla_put_failure;
 
-        stats = dev_get_stats(dev);
+        stats = dev_get_stats(dev, &temp);
         copy_rtnl_link_stats(nla_data(attr), stats);
 
         attr = nla_reserve(skb, IFLA_STATS64,