linux-kernel - Re: [PATCH] net: ethernet: Fixe issue in nvmem_get_mac

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Message-ID: <01100196afe6ce73-82eaa239-15a5-48d0-bca7-f5870ec0569e-000000@eu-north-1.amazonses.com>
Date: Thu, 8 May 2025 12:37:41 +0000
From: Ozgur Kara <ozgur@...sey.org>
To: Andrew Lunn <andrew@...n.ch>
Cc: Ozgur Kara <ozgur@...sey.org>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, netdev@...r.kernel.org, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Simon Horman <horms@...nel.org>, 
	Nikolay Aleksandrov <razor@...ckwall.org>, 
	Alexei Starovoitov <ast@...nel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] net: ethernet: Fixe issue in nvmem_get_mac_address()
 where invalid mac addresses

Andrew Lunn <andrew@...n.ch>, 8 May 2025 Per, 15:01 tarihinde şunu yazdı:
>
> On Thu, May 08, 2025 at 02:14:00AM +0000, Ozgur Kara wrote:
> > From: Ozgur Karatas <ozgur@...sey.org>
> >
> > it's necessary to log error returned from
> > fwnode_property_read_u8_array because there is no detailed information
> > when addr returns an invalid mac address.
> >
> > kfree(mac) should actually be marked as kfree((void *)mac) because mac
> > pointer is of type const void * and type conversion is required so
> > data returned from nvmem_cell_read() is of same type.
>
> What warning do you see from the compiler?

Hello Andrew,

My compiler didnt give an error to this but we had to declare that
pointer would be used as a memory block not data and i added (void *)
because i was hoping that mac variable would use it to safely remove
const so expect a parameter of type void * avoid possible compiler
incompatibilities.
I guess, however if mac is a pointer of a different type (i guess)  we
use kfree(mac) without converting it to (void *) type compiler may
give an error.

For example will give error:

int mac = 10;
kfree(mac);

because pointer was of a type incompatible with const void * and i
think its not a compiler error, in this case it could be an error at
runtime bug and type of error could turn into a memory leak.
for example use clang i guess give error warning passing argument 1 of
kfree qualifier from pointer target type.

am i thinking wrong?

> > @@ -565,11 +565,16 @@ static int fwnode_get_mac_addr(struct
> > fwnode_handle *fwnode,
> >         int ret;
> >
> >         ret = fwnode_property_read_u8_array(fwnode, name, addr, ETH_ALEN);
> > -       if (ret)
> > +       if (ret) {
> > +               pr_err("Failed to read MAC address property %s\n", name);
> >                 return ret;
> > +        }
> >
> > -       if (!is_valid_ether_addr(addr))
> > +       if (!is_valid_ether_addr(addr)) {
> > +               pr_err("Invalid MAC address read for %s\n", name);
> >                 return -EINVAL;
> > +        }
> > +
> >         return 0;
> >  }
>
> Look at how it is used:
>
> int of_get_mac_address(struct device_node *np, u8 *addr)
> {
>         int ret;
>
>         if (!np)
>                 return -ENODEV;
>
>         ret = of_get_mac_addr(np, "mac-address", addr);
>         if (!ret)
>                 return 0;
>
>         ret = of_get_mac_addr(np, "local-mac-address", addr);
>         if (!ret)
>                 return 0;
>
>         ret = of_get_mac_addr(np, "address", addr);
>         if (!ret)
>                 return 0;
>
>         return of_get_mac_address_nvmem(np, addr);
> }
>
> We keep trying until we find a MAC address. It is not an error if a
> source does not have a MAC address, we just keep going and try the
> next.
>
> So you should not print an message if the property does not
> exist. Other errors, EIO, EINVAL, etc, are O.K. to print a warning.
>

ah, i understand that its already checked continuously via a loop so
it would be unnecessary if i printed an error message for
of_get_mac_addr.
hm this is an expected situation and device are just moving on to the
next property I understand thank you.
I will look at code again and understand it better.

Thanks for help,
Regards

Ozgur

>     Andrew
>
> ---
> pw-bot: cr
>
>