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From:   Felix Riemann <svc.sw.rte.linux@sma.de>
To:     <netdev@vger.kernel.org>
CC:     <linux-kernel@vger.kernel.org>, Eric Dumazet <edumazet@google.com>,
        "Jakub Kicinski" <kuba@kernel.org>,
        "David S. Miller" <davem@davemloft.net>,
        "Felix Riemann" <felix.riemann@sma.de>
Subject: [PATCH] net: Fix unwanted sign extension in netdev_stats_to_stats64()
Date:   Fri, 10 Feb 2023 13:36:44 +0100
Message-ID: <20230210123644.489-1-svc.sw.rte.linux@sma.de>
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From: Felix Riemann <felix.riemann@sma.de>

When converting net_device_stats to rtnl_link_stats64 sign extension
is triggered on ILP32 machines as 6c1c509778 changed the previous
"ulong -> u64" conversion to "long -> u64" by accessing the
net_device_stats fields through a (signed) atomic_long_t.

This causes for example the received bytes counter to jump to 16EiB after
having received 2^31 bytes. Casting the atomic value to "unsigned long"
beforehand converting it into u64 avoids this.

Fixes: 6c1c5097781f ("net: add atomic_long_t to net_device_stats fields")
Signed-off-by: Felix Riemann <felix.riemann@sma.de>
---
 net/core/dev.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index b76fb37b381e..ea0a7bac1e5c 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -10375,7 +10375,7 @@ void netdev_stats_to_stats64(struct rtnl_link_stats64 *stats64,
 
 	BUILD_BUG_ON(n > sizeof(*stats64) / sizeof(u64));
 	for (i = 0; i < n; i++)
-		dst[i] = atomic_long_read(&src[i]);
+		dst[i] = (unsigned long)atomic_long_read(&src[i]);
 	/* zero out counters that only exist in rtnl_link_stats64 */
 	memset((char *)stats64 + n * sizeof(u64), 0,
 	       sizeof(*stats64) - n * sizeof(u64));
-- 
2.35.3