linux-kernel - Re: [PATCH net-next 1/7] net: stmmac: replace memcpy with strscpy in ethtool

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Message-ID: <20250827191315.GQ10519@horms.kernel.org>
Date: Wed, 27 Aug 2025 20:13:15 +0100
From: Simon Horman <horms@...nel.org>
To: Konrad Leszczynski <konrad.leszczynski@...el.com>
Cc: davem@...emloft.net, andrew+netdev@...n.ch, edumazet@...gle.com,
	kuba@...nel.org, pabeni@...hat.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, cezary.rojewski@...el.com,
	sebastian.basierski@...el.com, Kees Cook <kees@...nel.org>
Subject: Re: [PATCH net-next 1/7] net: stmmac: replace memcpy with strscpy in
 ethtool

+ Kees

On Tue, Aug 26, 2025 at 01:32:41PM +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
> 
> [  +0.000005] Call Trace:
> [  +0.000004]  <TASK>
> [  +0.000003]  dump_stack_lvl+0x6c/0x90
> [  +0.000016]  print_report+0xce/0x610
> [  +0.000011]  ? stmmac_get_strings+0x17d/0x520 [stmmac]
> [  +0.000108]  ? kasan_addr_to_slab+0xd/0xa0
> [  +0.000008]  ? stmmac_get_strings+0x17d/0x520 [stmmac]
> [  +0.000101]  kasan_report+0xd4/0x110
> [  +0.000010]  ? stmmac_get_strings+0x17d/0x520 [stmmac]
> [  +0.000102]  kasan_check_range+0x3a/0x1c0
> [  +0.000010]  __asan_memcpy+0x24/0x70
> [  +0.000008]  stmmac_get_strings+0x17d/0x520 [stmmac]
> 
> Reviewed-by: Sebastian Basierski <sebastian.basierski@...el.com>
> Signed-off-by: Konrad Leszczynski <konrad.leszczynski@...el.com>

Hi Konrad,

As mentioned by Vadim elsewhere, as this is a fix it should
be part of a separate series targeted at net.

And it should have a Fixes tag.

Also, as a follow-up for net-next, it might be nice
to move stmmac_get_strings() to use an appropriate combination
of ethtool_puts() and ethtool_cpu().

See: commit 151e13ece86d ("net: ethtool: Adjust exactly ETH_GSTRING_LEN-long stats to use memcpy")

The code change itself looks good to me.

> ---
>  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 f702f7b7bf9f..219a2df578ae 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_ethtool.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_ethtool.c
> @@ -795,7 +795,7 @@ 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;
>  				}
>  			}
> -- 
> 2.34.1
> 
>