linux-kernel - Re: [PATCH net-next v1] hinic: fix strncpy output truncated compile warnings

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Date:   Sun, 9 Aug 2020 11:35:50 +0800
From:   "luobin (L)" <luobin9@...wei.com>
To:     David Laight <David.Laight@...LAB.COM>,
        "davem@...emloft.net" <davem@...emloft.net>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "luoxianjun@...wei.com" <luoxianjun@...wei.com>,
        "yin.yinshi@...wei.com" <yin.yinshi@...wei.com>,
        "cloud.wangxiaoyun@...wei.com" <cloud.wangxiaoyun@...wei.com>,
        "chiqijun@...wei.com" <chiqijun@...wei.com>
Subject: Re: [PATCH net-next v1] hinic: fix strncpy output truncated compile
 warnings

On 2020/8/8 20:50, David Laight wrote:
> From: luobin (L)
>> Sent: 08 August 2020 04:37
>>
>> On 2020/8/7 17:32, David Laight wrote:
>>> From: Luo bin
>>>> Sent: 07 August 2020 03:09
>>>>
>>>> fix the compile warnings of 'strncpy' output truncated before
>>>> terminating nul copying N bytes from a string of the same length
>>>>
>>>> Signed-off-by: Luo bin <luobin9@...wei.com>
>>>> Reported-by: kernel test robot <lkp@...el.com>
>>>> ---
>>>> V0~V1:
>>>> - use the strlen()+1 pattern consistently
>>>>
>>>>  drivers/net/ethernet/huawei/hinic/hinic_devlink.c | 8 ++++----
>>>>  1 file changed, 4 insertions(+), 4 deletions(-)
>>>>
>>>> diff --git a/drivers/net/ethernet/huawei/hinic/hinic_devlink.c
>>>> b/drivers/net/ethernet/huawei/hinic/hinic_devlink.c
>>>> index c6adc776f3c8..1ec88ebf81d6 100644
>>>> --- a/drivers/net/ethernet/huawei/hinic/hinic_devlink.c
>>>> +++ b/drivers/net/ethernet/huawei/hinic/hinic_devlink.c
>>>> @@ -342,9 +342,9 @@ static int chip_fault_show(struct devlink_fmsg *fmsg,
>>>>
>>>>  	level = event->event.chip.err_level;
>>>>  	if (level < FAULT_LEVEL_MAX)
>>>> -		strncpy(level_str, fault_level[level], strlen(fault_level[level]));
>>>> +		strncpy(level_str, fault_level[level], strlen(fault_level[level]) + 1);
>>>
>>> Have you even considered what that code is actually doing?
>>>
>>> 	David
>>
>> I'm sorry that I haven't got what you mean and I haven't found any defects in that code. Can you
>> explain more to me?
> 
> If you can't see it you probably shouldn't be submitting patches....
> 
> Consider what happens when the string is long.
> 
> 	David
> 
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> Registration No: 1397386 (Wales)
> 
Thanks for your explanation and review. The fault_level[level] is a fixed and NUL-terminated character
string in that code and its length is smaller than the dest buffer size so I think using
strlen(fault_level[level]) + 1 will not overflow the destination buffer. But using strncpy() on
NUL-terminated strings is dangerous indeed and there is totally no need to use it in that code
as Kees points out.