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

From: Arnd Bergmann
Date: Mon Nov 22 2021 - 10:07:15 EST

On Mon, Nov 22, 2021 at 4:02 PM Arnd Bergmann <arnd@xxxxxxxxxx> wrote:
> From: Arnd Bergmann <arnd@xxxxxxxx>
> 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@xxxxxxxx>

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