linux-kernel - Re: [PATCH v3] net: phy: fix uninitalized WOL parameters in phy_ethtool_get

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Message-Id: <20140313.153832.967564223480298567.davem@davemloft.net>
Date:	Thu, 13 Mar 2014 15:38:32 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	sebastian.hesselbarth@...il.com
Cc:	f.fainelli@...il.com, ben@...adent.org.uk, netdev@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] net: phy: fix uninitalized WOL parameters in
 phy_ethtool_get_wol

From: Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
Date: Wed, 12 Mar 2014 00:02:55 +0100

> phy_ethtool_get_wol is a helper to get current WOL settings from
> a phy device. When using this helper on a PHY without .get_wol
> callback, struct ethtool_wolinfo is never set-up correctly and
> may contain misleading information about WOL status.
> 
> To fix this, always zero relevant fields of struct ethtool_wolinfo
> regardless of .get_wol callback availability.
> 
> Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
> Reviewed-by: Florian Fainelli <f.fainelli@...il.com>

I'm starting to see this situation more clearly now, especially with
Ben's most recent commentary.

The basic notion is that one must do ethtool ops are designed such that
the top-level execution context in net/core/ethtool.c takes care of
initializing the structure.

In this case, we're referring specifically to ethtool_get_wol(), which
runs any time ETHTOOL_GWOL is requested.

Therefore no ethtool_ops->get_wol() implementation should duplicate
this work, that goes for all of such cases which invoke the function
we are talking about here, phy_ethtool_get_wol().

So the first change is definitely to remove:

	wol->supported = 0;
	wol->wolopts = 0;

from:

drivers/net/ethernet/marvell/mv643xx_eth.c:mv643xx_eth_get_wol()
drivers/net/ethernet/ti/cpsw.c:cpsw_get_wol()

Next, I think phy_suspend() must create the same environment the
call sites above guarentee for phy_ethtool_get_wol(), namely
by changing the declaration of 'wol' to:

	struct ethtool_wolinfo wol = { .cmd = ETHTOOL_GWOL };

which will cause the compiler to clear out the rest of the structure
for us, as the same declaration does in ethtool_get_wol().

Finally, purge the spurious clears in phydev_ops->get_wol(), namely
in at803x_get_wol() and m88e1318_get_wol().

So, to reiterate, OPS never have to be mindful of initializing the
ethtool result with zeros.  However, anyone who calls into OPS
directly must provide said expected state.

Are we all on the same page now?
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