[PATCH v2 net] net: dsa: fix error code getting shifted with 4 in dsa_slave_get_sset_count

[PATCH v2 net] net: dsa: fix error code getting shifted with 4 in dsa_slave_get_sset_count

[Vladimir Oltean]

From: Vladimir Oltean <vladimir.oltean@nxp.com>

DSA implements a bunch of 'standardized' ethtool statistics counters,
namely tx_packets, tx_bytes, rx_packets, rx_bytes. So whatever the
hardware driver returns in .get_sset_count(), we need to add 4 to that.

That is ok, except that .get_sset_count() can return a negative error
code, for example:

b53_get_sset_count
-> phy_ethtool_get_sset_count
   -> return -EIO

-EIO is -5, and with 4 added to it, it becomes -1, aka -EPERM. One can
imagine that certain error codes may even become positive, although
based on code inspection I did not see instances of that.

Check the error code first, if it is negative return it as-is.

Based on a similar patch for dsa_master_get_strings from Dan Carpenter:
https://patchwork.kernel.org/project/netdevbpf/patch/YJaSe3RPgn7gKxZv@mwanda/

Fixes: 91da11f870f0 ("net: Distributed Switch Architecture protocol support")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
---
v1 -> v2: preserved variable name of "count" instead of "err".

 net/dsa/slave.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/net/dsa/slave.c b/net/dsa/slave.c
index 3689ffa2dbb8..988af45dd38f 100644
--- a/net/dsa/slave.c
+++ b/net/dsa/slave.c
@@ -798,13 +798,15 @@ static int dsa_slave_get_sset_count(struct net_device *dev, int sset)
 	struct dsa_switch *ds = dp->ds;
 
 	if (sset == ETH_SS_STATS) {
-		int count;
+		int count = 0;
 
-		count = 4;
-		if (ds->ops->get_sset_count)
-			count += ds->ops->get_sset_count(ds, dp->index, sset);
+		if (ds->ops->get_sset_count) {
+			count = ds->ops->get_sset_count(ds, dp->index, sset);
+			if (count < 0)
+				return count;
+		}
 
-		return count;
+		return count + 4;
 	} else if (sset ==  ETH_SS_TEST) {
 		return net_selftest_get_count();
 	}
-- 
2.25.1

Re: [PATCH v2 net] net: dsa: fix error code getting shifted with 4 in dsa_slave_get_sset_count

[Andrew Lunn]

On Sun, May 09, 2021 at 10:33:38PM +0300, Vladimir Oltean wrote:
> From: Vladimir Oltean <vladimir.oltean@nxp.com>
> 
> DSA implements a bunch of 'standardized' ethtool statistics counters,
> namely tx_packets, tx_bytes, rx_packets, rx_bytes. So whatever the
> hardware driver returns in .get_sset_count(), we need to add 4 to that.
> 
> That is ok, except that .get_sset_count() can return a negative error
> code, for example:
> 
> b53_get_sset_count
> -> phy_ethtool_get_sset_count
>    -> return -EIO
> 
> -EIO is -5, and with 4 added to it, it becomes -1, aka -EPERM. One can
> imagine that certain error codes may even become positive, although
> based on code inspection I did not see instances of that.
> 
> Check the error code first, if it is negative return it as-is.
> 
> Based on a similar patch for dsa_master_get_strings from Dan Carpenter:
> https://patchwork.kernel.org/project/netdevbpf/patch/YJaSe3RPgn7gKxZv@mwanda/
> 
> Fixes: 91da11f870f0 ("net: Distributed Switch Architecture protocol support")
> Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
> Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>

Reviewed-by: Andrew Lunn <andrew@lunn.ch>

    Andrew

Re: [PATCH v2 net] net: dsa: fix error code getting shifted with 4 in dsa_slave_get_sset_count

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (refs/heads/master):

On Sun,  9 May 2021 22:33:38 +0300 you wrote:
> From: Vladimir Oltean <vladimir.oltean@nxp.com>
> 
> DSA implements a bunch of 'standardized' ethtool statistics counters,
> namely tx_packets, tx_bytes, rx_packets, rx_bytes. So whatever the
> hardware driver returns in .get_sset_count(), we need to add 4 to that.
> 
> That is ok, except that .get_sset_count() can return a negative error
> code, for example:
> 
> [...]

Here is the summary with links:
  - [v2,net] net: dsa: fix error code getting shifted with 4 in dsa_slave_get_sset_count
    https://git.kernel.org/netdev/net/c/b94cbc909f1d

You are awesome, thank you!
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