netdev - Re: [PATCH] nixge: fix mac address error handling again

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Date:   Mon, 22 Nov 2021 16:06:54 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Moritz Fischer <mdf@...nel.org>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Yang Yingliang <yangyingliang@...wei.com>,
        Yufeng Mo <moyufeng@...wei.com>,
        Huazhong Tan <tanhuazhong@...wei.com>,
        Cai Huoqing <caihuoqing@...du.com>,
        Networking <netdev@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] nixge: fix mac address error handling again

On Mon, Nov 22, 2021 at 4:02 PM Arnd Bergmann <arnd@...nel.org> wrote:
>
> From: Arnd Bergmann <arnd@...db.de>
>
> The change to eth_hw_addr_set() caused gcc to correctly spot a
> bug that was introduced in an earlier incorrect fix:
>
> In file included from include/linux/etherdevice.h:21,
>                  from drivers/net/ethernet/ni/nixge.c:7:
> In function '__dev_addr_set',
>     inlined from 'eth_hw_addr_set' at include/linux/etherdevice.h:319:2,
>     inlined from 'nixge_probe' at drivers/net/ethernet/ni/nixge.c:1286:3:
> include/linux/netdevice.h:4648:9: error: 'memcpy' reading 6 bytes from a region of size 0 [-Werror=stringop-overread]
>  4648 |         memcpy(dev->dev_addr, addr, len);
>       |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> As nixge_get_nvmem_address() can return either NULL or an error
> pointer, the NULL check is wrong, and we can end up reading from
> ERR_PTR(-EOPNOTSUPP), which gcc knows to contain zero readable
> bytes.
>
> Make the function always return an error pointer again but fix
> the check to match that.
>
> Fixes: f3956ebb3bf0 ("ethernet: use eth_hw_addr_set() instead of ether_addr_copy()")
> Fixes: abcd3d6fc640 ("net: nixge: Fix error path for obtaining mac address")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Sorry, I sent out the wrong patch, this version fixes the bug but not the
warning. v2 is the version I actually tested successfully.

       Arnd