netdev - [PATCH net-next v1 5/7] ethtool: add helper to prevent invalid statistics exposure to userspace

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Message-Id: <20241203075622.2452169-6-o.rempel@pengutronix.de>
Date: Tue,  3 Dec 2024 08:56:19 +0100
From: Oleksij Rempel <o.rempel@...gutronix.de>
To: "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	Heiner Kallweit <hkallweit1@...il.com>,
	Jonathan Corbet <corbet@....net>
Cc: Oleksij Rempel <o.rempel@...gutronix.de>,
	kernel@...gutronix.de,
	linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org,
	Simon Horman <horms@...nel.org>,
	Russell King <linux@...linux.org.uk>,
	Maxime Chevallier <maxime.chevallier@...tlin.com>,
	linux-doc@...r.kernel.org
Subject: [PATCH net-next v1 5/7] ethtool: add helper to prevent invalid statistics exposure to userspace

Introduce a new helper function, `ethtool_stat_add`, to update 64-bit
statistics with proper handling of the reserved value
`ETHTOOL_STAT_NOT_SET`. This ensures that statistics remain valid and
are always reported to userspace, even if the driver accidentally sets
`ETHTOOL_STAT_NOT_SET` during an update.

Signed-off-by: Oleksij Rempel <o.rempel@...gutronix.de>
---
 include/linux/ethtool.h | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/include/linux/ethtool.h b/include/linux/ethtool.h
index b0ed740ca749..657bd69ddaf7 100644
--- a/include/linux/ethtool.h
+++ b/include/linux/ethtool.h
@@ -371,6 +371,22 @@ static inline void ethtool_stats_init(u64 *stats, unsigned int n)
 		stats[n] = ETHTOOL_STAT_NOT_SET;
 }
 
+/**
+ * ethtool_stat_add - Add a value to a u64 statistic with wraparound handling
+ * @stat: Pointer to the statistic to update
+ * @value: Value to add to the statistic
+ *
+ * Adds the specified value to a u64 statistic. If the result of the addition
+ * equals the reserved value (`ETHTOOL_STAT_NOT_SET`), it increments the result
+ * by 1 to avoid the reserved value.
+ */
+static inline void ethtool_stat_add(u64 *stat, u64 value)
+{
+	*stat += value;
+	if (*stat == ETHTOOL_STAT_NOT_SET)
+		(*stat)++;
+}
+
 /* Basic IEEE 802.3 MAC statistics (30.3.1.1.*), not otherwise exposed
  * via a more targeted API.
  */
-- 
2.39.5