Re: [PATCH net 1/3] net: stmmac: replace memcpy with strscpy in ethtool

[Sebastian Basierski <sebastian.basierski@intel.com>]

On 9/1/2025 9:59 PM, Jakub Kicinski wrote:
> On Thu, 28 Aug 2025 12:02:35 +0200 Konrad Leszczynski wrote:
>> Fix kernel exception by replacing memcpy with strscpy when used with
>> safety feature strings in ethtool logic.
>>
>> [  +0.000023] BUG: KASAN: global-out-of-bounds in stmmac_get_strings+0x17d/0x520 [stmmac]
>> [  +0.000115] Read of size 32 at addr ffffffffc0cfab20 by task ethtool/2571
> If you hit this with upstream code please mention which string
> is not padded. If this can't happen with upstream platforms --
> there is no upstream bug. BTW ethtool_puts() is a better choice.
Hi Jakub,
Sorry for late answer to your review.
I double checked and made sure this bug reproduces on upstream platform.
Bug seems to appear on first string - i will add this information to 
commit message.
Also thanks for code change suggestion, indeed, it looks much better.

Best Regards,
Sebastian
>> Fixes: 8bf993a5877e8a0a ("net: stmmac: Add support for DWMAC5 and implement Safety Features")
>> Reviewed-by: Sebastian Basierski <sebastian.basierski@intel.com>
>> Reviewed-by: Cezary Rojewski <cezary.rojewski@intel.com>
>> Signed-off-by: Konrad Leszczynski <konrad.leszczynski@intel.com>
>> ---
>>   drivers/net/ethernet/stmicro/stmmac/stmmac_ethtool.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_ethtool.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_ethtool.c
>> index 77758a7299b4..0433be4bd0c4 100644
>> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_ethtool.c
>> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_ethtool.c
>> @@ -752,7 +752,7 @@ static void stmmac_get_strings(struct net_device *dev, u32 stringset, u8 *data)
>>   				if (!stmmac_safety_feat_dump(priv,
>>   							&priv->sstats, i,
>>   							NULL, &desc)) {
>> -					memcpy(p, desc, ETH_GSTRING_LEN);
>> +					strscpy(p, desc, ETH_GSTRING_LEN);
>>   					p += ETH_GSTRING_LEN;
>>   				}