ethtool: Update ethtool_rxnfc::rule_cnt on return from ETHTOOL_GRXCLSRLALL

A user-space process must use ETHTOOL_GRXCLSRLCNT to find the number
of classification rules, then allocate a buffer of the right size,
then use ETHTOOL_GRXCLSRLALL to fill the buffer.  If some other
process inserts or deletes a rule between those two operations,
the user buffer might turn out to be the wrong size.

If it's too small, the return value will be -EMSGSIZE.  But if it's
too large, there is no indication of this.  Fix this by updating
the rule_cnt field on return.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

4 files changed, 8 insertions, 3 deletions

diff --git a/drivers/net/ethernet/freescale/gianfar_ethtool.c b/drivers/net/ethernet/freescale/gianfar_ethtool.c
index 42238301c425..f30b96fee840 100644
--- a/drivers/net/ethernet/freescale/gianfar_ethtool.c
+++ b/drivers/net/ethernet/freescale/gianfar_ethtool.c
@@ -1676,6 +1676,7 @@ static int gfar_get_cls_all(struct gfar_private *priv,
         }
 
         cmd->data = MAX_FILER_IDX;
+        cmd->rule_cnt = i;
 
         return 0;
 }
diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_ethtool.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_ethtool.c
index c0003babc06b..b8410bcaa898 100644
--- a/drivers/net/ethernet/intel/ixgbe/ixgbe_ethtool.c
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_ethtool.c
@@ -2283,6 +2283,8 @@ static int ixgbe_get_ethtool_fdir_all(struct ixgbe_adapter *adapter,
                 cnt++;
         }
 
+        cmd->rule_cnt = cnt;
+
         return 0;
 }
 
diff --git a/drivers/net/ethernet/sun/niu.c b/drivers/net/ethernet/sun/niu.c
index 5e1e1d2748ae..d1338885dc8b 100644
--- a/drivers/net/ethernet/sun/niu.c
+++ b/drivers/net/ethernet/sun/niu.c
@@ -7299,6 +7299,8 @@ static int niu_get_ethtool_tcam_all(struct niu *np,
         }
         niu_unlock_parent(np, flags);
 
+        nfc->rule_cnt = cnt;
+
         return ret;
 }
 
diff --git a/include/linux/ethtool.h b/include/linux/ethtool.h
index 5d4a06accd82..45f00b61c096 100644
--- a/include/linux/ethtool.h
+++ b/include/linux/ethtool.h
@@ -496,9 +496,9 @@ struct ethtool_rx_flow_spec {
  *
  * For %ETHTOOL_GRXCLSRLALL, @rule_cnt specifies the array size of the
  * user buffer for @rule_locs on entry.  On return, @data is the size
- * of the rule table and @rule_locs contains the locations of the
- * defined rules.  Drivers must use the second parameter to get_rxnfc()
- * instead of @rule_locs.
+ * of the rule table, @rule_cnt is the number of defined rules, and
+ * @rule_locs contains the locations of the defined rules.  Drivers
+ * must use the second parameter to get_rxnfc() instead of @rule_locs.
  *
  * For %ETHTOOL_SRXCLSRLINS, @fs specifies the rule to add or update.
  * @fs.@location specifies the location to use and must not be ignored.