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

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Date: Mon, 20 Nov 2023 12:41:51 +0100
From: Alexander Lobakin <aleksander.lobakin@...el.com>
To: Kunwu Chan <chentao@...inos.cn>
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

From: Kunwu Chan <chentao@...inos.cn>
Date: Sun, 19 Nov 2023 23:12:09 +0800

> 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?

You have a kfree() at the end of the function.

Generally speaking, 'ka' stands for "[kernel] allocate" and you also
need to pass GPF_ as the second argument. Enough hints that you need to
free the pointer after using it I would say.

> 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

Thanks,
Olek