linux-kernel - Re: [PATCH iwl-next] i40e: Use correct buffer size

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Message-ID: <4b551600-f1a3-4efe-b3e9-99cb4536f487@kylinos.cn>
Date:   Sun, 19 Nov 2023 23:12:09 +0800
From:   Kunwu Chan <chentao@...inos.cn>
To:     Alexander Lobakin <aleksander.lobakin@...el.com>
Cc:     horms@...nel.org, anthony.l.nguyen@...el.com, davem@...emloft.net,
        edumazet@...gle.com, intel-wired-lan@...ts.osuosl.org,
        jeffrey.t.kirsher@...el.com, jesse.brandeburg@...el.com,
        kuba@...nel.org, kunwu.chan@...mail.com,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        pabeni@...hat.com, shannon.nelson@....com
Subject: Re: [PATCH iwl-next] i40e: Use correct buffer size

Hi Alexander,
Thank you so much for your reply, I looked at the modification you 
mentioned, it's really cool. I'll definitely try it next time.

But when using it, will it be easy to forget to free up memory?
Although 'kmalloc_track_caller' is used, according to my understanding, 
it is also necessary to release the memory at the end of use.

On 2023/11/15 23:39, Alexander Lobakin wrote:
> From: Kunwu Chan <chentao@...inos.cn>
> Date: Wed, 15 Nov 2023 11:14:44 +0800
> 
>> The size of "i40e_dbg_command_buf" is 256, the size of "name"
>> depends on "IFNAMSIZ", plus a null character and format size,
>> the total size is more than 256, fix it.
>>
>> Signed-off-by: Kunwu Chan <chentao@...inos.cn>
>> Suggested-by: Simon Horman <horms@...nel.org>
>> ---
>>   drivers/net/ethernet/intel/i40e/i40e_debugfs.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/net/ethernet/intel/i40e/i40e_debugfs.c b/drivers/net/ethernet/intel/i40e/i40e_debugfs.c
>> index 999c9708def5..e3b939c67cfe 100644
>> --- a/drivers/net/ethernet/intel/i40e/i40e_debugfs.c
>> +++ b/drivers/net/ethernet/intel/i40e/i40e_debugfs.c
>> @@ -72,7 +72,7 @@ static ssize_t i40e_dbg_command_read(struct file *filp, char __user *buffer,
>>   {
>>   	struct i40e_pf *pf = filp->private_data;
>>   	int bytes_not_copied;
>> -	int buf_size = 256;
>> +	int buf_size = IFNAMSIZ + sizeof(i40e_dbg_command_buf) + 4;
> 
> Reverse Christmas Tree style? Should be the first one in the declaration
> list.
> 
>>   	char *buf;
>>   	int len;
> 
> You can fix it in a different way. Given that there's a kzalloc() either
> way, why not allocate the precise required amount of bytes by using
> kasprintf() instead of kzalloc() + snprintf()? You wouldn't need to
> calculate any buffer sizes etc. this way.
> 
> Thanks,
> Olek