linux-kernel - Re: [PATCH] kdb: Fix bound check compiler warning

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Date:   Mon, 13 May 2019 11:39:47 +0800
From:   Wenlin Kang <wenlin.kang@...driver.com>
To:     Daniel Thompson <daniel.thompson@...aro.org>
CC:     <jason.wessel@...driver.com>, <prarit@...hat.com>,
        <kgdb-bugreport@...ts.sourceforge.net>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kdb: Fix bound check compiler warning

On 5/12/19 5:00 PM, Daniel Thompson wrote:
> On Thu, May 09, 2019 at 10:56:03AM +0800, Wenlin Kang wrote:
>> On 5/8/19 4:16 PM, Daniel Thompson wrote:
>>> On Wed, May 08, 2019 at 09:52:39AM +0800, Wenlin Kang wrote:
>>>> The strncpy() function may leave the destination string buffer
>>>> unterminated, better use strlcpy() instead.
>>>>
>>>> This fixes the following warning with gcc 8.2:
>>>>
>>>> kernel/debug/kdb/kdb_io.c: In function 'kdb_getstr':
>>>> kernel/debug/kdb/kdb_io.c:449:3: warning: 'strncpy' specified bound 256 equals destination size [-Wstringop-truncation]
>>>>      strncpy(kdb_prompt_str, prompt, CMD_BUFLEN);
>>>>      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>>>
>>>> Signed-off-by: Wenlin Kang <wenlin.kang@...driver.com>
>>>> ---
>>>>    kernel/debug/kdb/kdb_io.c | 2 +-
>>>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c
>>>> index 6a4b414..7fd4513 100644
>>>> --- a/kernel/debug/kdb/kdb_io.c
>>>> +++ b/kernel/debug/kdb/kdb_io.c
>>>> @@ -446,7 +446,7 @@ static char *kdb_read(char *buffer, size_t bufsize)
>>>>    char *kdb_getstr(char *buffer, size_t bufsize, const char *prompt)
>>>>    {
>>>>    	if (prompt && kdb_prompt_str != prompt)
>>>> -		strncpy(kdb_prompt_str, prompt, CMD_BUFLEN);
>>>> +		strlcpy(kdb_prompt_str, prompt, CMD_BUFLEN);
>>> Shouldn't that be strscpy?
>>
>> Hi Daniel
>>
>> I thought about strscpy, but I think strlcpy is better, because it only copy
>> the real number of characters if src string less than that size.
> Sorry, I'm confused by this. What behavior does strscpy() have that you
> consider undesirable in this case?


Hi Daniel

I checked strscpy() again, and think either is fine to me, if you think 
strscpy() is better, I can change it to this, and send v2, thanks for 
your review.


>
> Daniel.
>

-- 
Thanks,
Wenlin Kang