netdev - Re: [PATCH net-next 1/8] atm: use min() to simplify the code

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Message-ID: <469c7954-9a50-4822-a862-21decb1e8850@intel.com>
Date: Thu, 22 Aug 2024 13:20:17 -0700
From: Jacob Keller <jacob.e.keller@...el.com>
To: Li Zetao <lizetao1@...wei.com>, "Dr. David Alan Gilbert"
	<linux@...blig.org>
CC: <davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>,
	<pabeni@...hat.com>, <marcel@...tmann.org>, <johan.hedberg@...il.com>,
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	<linux-bluetooth@...r.kernel.org>, <ceph-devel@...r.kernel.org>,
	<linux-nfs@...r.kernel.org>, <tipc-discussion@...ts.sourceforge.net>
Subject: Re: [PATCH net-next 1/8] atm: use min() to simplify the code



On 8/22/2024 6:50 AM, Li Zetao wrote:
> Hi,
> 
> 在 2024/8/22 21:39, Dr. David Alan Gilbert 写道:
>> * Li Zetao (lizetao1@...wei.com) wrote:
>>> When copying data to user, it needs to determine the copy length.
>>> It is easier to understand using min() here.
>>>
>>> Signed-off-by: Li Zetao <lizetao1@...wei.com>
>>> ---
>>>   net/atm/addr.c | 4 ++--
>>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/net/atm/addr.c b/net/atm/addr.c
>>> index 0530b63f509a..6c4c942b2cb9 100644
>>> --- a/net/atm/addr.c
>>> +++ b/net/atm/addr.c
>>> @@ -136,7 +136,7 @@ int atm_get_addr(struct atm_dev *dev, struct sockaddr_atmsvc __user * buf,
>>>   	unsigned long flags;
>>>   	struct atm_dev_addr *this;
>>>   	struct list_head *head;
>>> -	int total = 0, error;
>>> +	size_t total = 0, error;
>>
>> Aren't you accidentally changing the type of 'error' there, and the function
>> returns 'int'.
> This is intentionally modified because the input parameter size is of 
> type size_t. If total is of type int, the compiler will report an error 
> when the min() is called.
>>

Yea, but what you're missing is that error was an int before and is now
a size_t which can't be negative.

I think this either needs to be:

size_t total = 0;
int error

or better yet....

>> Dav
>>
>>
>>>   	struct sockaddr_atmsvc *tmp_buf, *tmp_bufp;
>>>   
>>>   	spin_lock_irqsave(&dev->lock, flags);
>>> @@ -155,7 +155,7 @@ int atm_get_addr(struct atm_dev *dev, struct sockaddr_atmsvc __user * buf,
>>>   	    memcpy(tmp_bufp++, &this->addr, sizeof(struct sockaddr_atmsvc));
>>>   	spin_unlock_irqrestore(&dev->lock, flags);
>>>   	error = total > size ? -E2BIG : total;
>>> -	if (copy_to_user(buf, tmp_buf, total < size ? total : size))
>>> +	if (copy_to_user(buf, tmp_buf, min(total, size)))
>>>   		error = -EFAULT;


Couldn't you just use min_t here instead of changing the variable sizes?

Thanks,
Jake