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

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Date: Tue, 30 May 2023 11:40:56 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Dan Carpenter <dan.carpenter@...aro.org>
Cc: Jakub Kicinski <kuba@...nel.org>, Andrew Lunn <andrew@...n.ch>, Russell
 King <linux@...linux.org.uk>, 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 Tue, 2023-05-30 at 12:23 +0300, Dan Carpenter wrote:
> On Tue, May 30, 2023 at 11:06:55AM +0200, Paolo Abeni wrote:
> > 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 don't see an issue in r8169_main.c and in drivers/net/phy/phy_device.c
> then I only find the bug from this patch.
> 
> regards,
> dan carpenter
> 
> diff --git a/include/linux/phy.h b/include/linux/phy.h
> index 6478838405a08..f05fc25b77583 100644
> --- a/include/linux/phy.h
> +++ b/include/linux/phy.h
> @@ -1173,6 +1173,7 @@ static inline int phy_read(struct phy_device *phydev, u32 regnum)
>  ({ \
>  	int __ret = read_poll_timeout(phy_read, val, val < 0 || (cond), \
>  		sleep_us, timeout_us, sleep_before_read, phydev, regnum); \
> +	BUILD_BUG_ON((typeof(val))~0ULL > 0);				\
>  	if (val < 0) \
>  		__ret = val; \
>  	if (__ret) \
> 

Uhm... I have no idea what happened to my build host. I did see more
build errors in previous attempt, but now I only observe the one you
address with this patch. I guess some PEBKAC hit me here.

/P