linux-kernel - Re: [PATCH] drivers/fsi/scom: Return -EFAULT if copy fails

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Message-ID: <7f1cd0ad-7991-af0c-a31a-84c261d4ca18@tom.com>
Date:   Tue, 23 May 2023 12:32:11 +0800
From:   Longsuhui <Jack_sun@....com>
To:     Guenter Roeck <linux@...ck-us.net>, Su Hui <suhui@...china.com>
Cc:     Jeremy Kerr <jk@...abs.org>, Joel Stanley <joel@....id.au>,
        Alistar Popple <alistair@...ple.id.au>,
        Eddie James <eajames@...ux.ibm.com>, eajames@...ibm.com,
        kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org,
        cbostic@...ux.vnet.ibm.com, linux-fsi@...ts.ozlabs.org
Subject: Re: [PATCH] drivers/fsi/scom: Return -EFAULT if copy fails


On 2023/5/23 06:30, Guenter Roeck wrote:
> On Fri, May 19, 2023 at 09:37:10AM +0800, Su Hui wrote:
>> The copy_to/from_user() functions return the number of bytes remaining
>> to be copied, but we want to return -EFAULT to the user.
>>
> Why ? EFAULT means that a bad address was provided, and it is not
> immediately obvious why that would be the case.

When copy_to/from_user() functions failed, the error code is  -EFAULT in most case.
	
	git grep -A1 "copy_from_user" | grep EFAULT | wc -l
     1985
	git grep -A1 "copy_to_user" | grep EFAULT | wc -l
      1871

I think return -EFAULT is also right in this case.

Su Hui

> Guenter
>
>> Fixes: 680ca6dcf5c2 ("drivers/fsi: Add SCOM FSI client device driver")
>> Signed-off-by: Su Hui <suhui@...china.com>
>> ---
>>   drivers/fsi/fsi-scom.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/fsi/fsi-scom.c b/drivers/fsi/fsi-scom.c
>> index bcb756dc9866..caaf7738eb98 100644
>> --- a/drivers/fsi/fsi-scom.c
>> +++ b/drivers/fsi/fsi-scom.c
>> @@ -335,7 +335,7 @@ static ssize_t scom_read(struct file *filep, char __user *buf, size_t len,
>>   	if (rc)
>>   		dev_dbg(dev, "copy to user failed:%d\n", rc);
>>   
>> -	return rc ? rc : len;
>> +	return rc ? -EFAULT : len;
>>   }
>>   
>>   static ssize_t scom_write(struct file *filep, const char __user *buf,
>> -- 
>> 2.30.2
>>