netdev - Re: [PATCH net-next 2/2] net: ena: simplify some pointer addition

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Message-ID: <pj41zlzfmfktdh.fsf@u95c7fd9b18a35b.ant.amazon.com>
Date: Mon, 4 Nov 2024 15:36:52 +0200
From: Shay Agroskin <shayagr@...zon.com>
To: Rosen Penev <rosenp@...il.com>
CC: <netdev@...r.kernel.org>, Arthur Kiyanovski <akiyano@...zon.com>, "David
 Arinzon" <darinzon@...zon.com>, Noam Dagan <ndagan@...zon.com>, "Saeed
 Bishara" <saeedb@...zon.com>, Andrew Lunn <andrew+netdev@...n.ch>, "David S.
 Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, "Jakub
 Kicinski" <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Jian Shen
	<shenjian15@...wei.com>, Salil Mehta <salil.mehta@...wei.com>, Jijie Shao
	<shaojijie@...wei.com>, open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next 2/2] net: ena: simplify some pointer addition


Rosen Penev <rosenp@...il.com> writes:

> Use ethtool_sprintf to simplify the code.
>
> Because strings_buf is separate from buf, it needs to be 
> incremented
> separately.
>
> Signed-off-by: Rosen Penev <rosenp@...il.com>
> ---
>  drivers/net/ethernet/amazon/ena/ena_ethtool.c | 17 
>  ++++++++---------
>  1 file changed, 8 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/net/ethernet/amazon/ena/ena_ethtool.c 
> b/drivers/net/ethernet/amazon/ena/ena_ethtool.c
> index fa9d7b8ec00d..96fa55a88faf 100644
> --- a/drivers/net/ethernet/amazon/ena/ena_ethtool.c
> +++ b/drivers/net/ethernet/amazon/ena/ena_ethtool.c
> @@ -1120,7 +1120,7 @@ static void ena_dump_stats_ex(struct 
> ena_adapter *adapter, u8 *buf)
>  	u8 *strings_buf;
>  	u64 *data_buf;
>  	int strings_num;
> -	int i, rc;
> +	int i;
>
>  	strings_num = ena_get_sw_stats_count(adapter);
>  	if (strings_num <= 0) {
> @@ -1149,17 +1149,16 @@ static void ena_dump_stats_ex(struct 
> ena_adapter *adapter, u8 *buf)
>  	/* If there is a buffer, dump stats, otherwise print them 
>  to dmesg */
>  	if (buf)
>  		for (i = 0; i < strings_num; i++) {
> -			rc = snprintf(buf, ETH_GSTRING_LEN + 
> sizeof(u64),
> -				      "%s %llu\n",
> -				      strings_buf + i * 
> ETH_GSTRING_LEN,
> -				      data_buf[i]);
> -			buf += rc;
> +			ethtool_sprintf(&buf, "%s %llu\n", 
> strings_buf,
> +					data_buf[i]);
> +			strings_buf += ETH_GSTRING_LEN;
>  		}
>  	else
> -		for (i = 0; i < strings_num; i++)
> +		for (i = 0; i < strings_num; i++) {
>  			netif_err(adapter, drv, netdev, "%s: 
>  %llu\n",
> -				  strings_buf + i * 
> ETH_GSTRING_LEN,
> -				  data_buf[i]);
> +				  strings_buf, data_buf[i]);
> +			strings_buf += ETH_GSTRING_LEN;
> +		}
>
>  	kfree(strings_buf);
>  	kfree(data_buf);

Thank you for submitting the patch. If I'm not mistaken, there are 
some bugs introduced here:

1. You update string_buf pointer itself, but later you pass the 
variable to kfree, this
   would likely end up freeing the wrong address (/causing a 
   kernel panic)
2. The ethtool_sprintf increases the `buf` pointer by 
ETH_GSTRING_LEN, while the previous code increased it
   by (ETH_GSTRING_LEN + sizeof(u64)) bytes.
   This causes a corruption in the buffer.

This function and mechanism is already planned for an overhaul in 
a future patch. We prefer to leave this patch out.

Thanks, Shay