linux-hardening - [PATCH] ethtool: stats: Use struct_group() to clear all stats at once

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Date:   Thu, 18 Nov 2021 12:34:56 -0800
From:   Kees Cook <keescook@...omium.org>
To:     "David S. Miller" <davem@...emloft.net>
Cc:     Kees Cook <keescook@...omium.org>,
        Jakub Kicinski <kuba@...nel.org>,
        Ido Schimmel <idosch@...dia.com>,
        YueHaibing <yuehaibing@...wei.com>, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: [PATCH] ethtool: stats: Use struct_group() to clear all stats at once

In preparation for FORTIFY_SOURCE performing compile-time and run-time
field bounds checking for memset(), avoid intentionally writing across
neighboring fields.

Add struct_group() to mark region of struct stats_reply_data that should
be initialized, which can now be done in a single memset() call.

Signed-off-by: Kees Cook <keescook@...omium.org>
---
 net/ethtool/stats.c | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/net/ethtool/stats.c b/net/ethtool/stats.c
index ec07f5765e03..a20e0a24ff61 100644
--- a/net/ethtool/stats.c
+++ b/net/ethtool/stats.c
@@ -14,10 +14,12 @@ struct stats_req_info {
 
 struct stats_reply_data {
 	struct ethnl_reply_data		base;
-	struct ethtool_eth_phy_stats	phy_stats;
-	struct ethtool_eth_mac_stats	mac_stats;
-	struct ethtool_eth_ctrl_stats	ctrl_stats;
-	struct ethtool_rmon_stats	rmon_stats;
+	struct_group(stats,
+		struct ethtool_eth_phy_stats	phy_stats;
+		struct ethtool_eth_mac_stats	mac_stats;
+		struct ethtool_eth_ctrl_stats	ctrl_stats;
+		struct ethtool_rmon_stats	rmon_stats;
+	);
 	const struct ethtool_rmon_hist_range	*rmon_ranges;
 };
 
@@ -117,10 +119,7 @@ static int stats_prepare_data(const struct ethnl_req_info *req_base,
 	/* Mark all stats as unset (see ETHTOOL_STAT_NOT_SET) to prevent them
 	 * from being reported to user space in case driver did not set them.
 	 */
-	memset(&data->phy_stats, 0xff, sizeof(data->phy_stats));
-	memset(&data->mac_stats, 0xff, sizeof(data->mac_stats));
-	memset(&data->ctrl_stats, 0xff, sizeof(data->ctrl_stats));
-	memset(&data->rmon_stats, 0xff, sizeof(data->rmon_stats));
+	memset(&data->stats, 0xff, sizeof(data->stats));
 
 	if (test_bit(ETHTOOL_STATS_ETH_PHY, req_info->stat_mask) &&
 	    dev->ethtool_ops->get_eth_phy_stats)
-- 
2.30.2