netdev - Re: [PATCH net] net: phy: fix a signedness bug in genphy

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Date: Tue, 30 May 2023 11:06:55 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Jakub Kicinski <kuba@...nel.org>, Andrew Lunn <andrew@...n.ch>, Russell
	King <linux@...linux.org.uk>
Cc: Dan Carpenter <dan.carpenter@...aro.org>, Oleksij Rempel
 <linux@...pel-privat.de>, Heiner Kallweit <hkallweit1@...il.com>, "David S.
 Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 netdev@...r.kernel.org,  kernel-janitors@...r.kernel.org
Subject: Re: [PATCH net] net: phy: fix a signedness bug in genphy_loopback()

On Mon, 2023-05-29 at 21:58 -0700, Jakub Kicinski wrote:
> On Fri, 26 May 2023 14:45:54 +0300 Dan Carpenter wrote:
> > The "val" variable is used to store error codes from phy_read() so
> > it needs to be signed for the error handling to work as expected.
> > 
> > Fixes: 014068dcb5b1 ("net: phy: genphy_loopback: add link speed configuration")
> > Signed-off-by: Dan Carpenter <dan.carpenter@...aro.org>
> 
> Is it going to be obvious to PHY-savvy folks that the val passed to
> phy_read_poll_timeout() must be an int? Is it a very common pattern?
> My outsider intuition is that since regs are 16b, u16 is reasonable,
> and more people may make the same mistake. Therefore we should try to
> fix phy_read_poll_timeout() instead to use a local variable like it
> does for __ret. 
> 
> Weaker version would be to add a compile time check to ensure val 
> is signed (assert(typeof(val)~0ULL < 0) or such?).

FTR, a BUILD_BUG_ON() the above check spots issues in several places
(e.g. r8169_main.c, drivers/net/phy/phy_device.c, ...)

I think it should be better resort to a signed local variable in
phy_read_poll_timeout()

Thanks,

Paolo