linux-kernel - Re: [PATCH] f2fs: Replace strncpy with memcpy

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Date:   Sun, 1 Jul 2018 19:16:37 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Chao Yu <yuchao0@...wei.com>
Cc:     Jaegeuk Kim <jaegeuk@...nel.org>,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] f2fs: Replace strncpy with memcpy

On 07/01/2018 06:53 PM, Chao Yu wrote:
> On 2018/7/2 4:57, Guenter Roeck wrote:
>> gcc 8.1.0 complains:
>>
>> fs/f2fs/namei.c: In function 'f2fs_update_extension_list':
>> fs/f2fs/namei.c:257:3: warning:
>> 	'strncpy' output truncated before terminating nul copying
>> 	as many bytes from a string as its length
>> fs/f2fs/namei.c:249:3: warning:
>> 	'strncpy' output truncated before terminating nul copying
>> 	as many bytes from a string as its length
>>
>> Using strncpy() is indeed less than perfect since the length of data to
>> be copied has already been determined with strlen(). Replace strncpy()
>> with memcpy() to address the warning and optimize the code a little.
>>
>> Signed-off-by: Guenter Roeck <linux@...ck-us.net>
>> ---
>>   fs/f2fs/namei.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/f2fs/namei.c b/fs/f2fs/namei.c
>> index 231b7f3ea7d3..e75607544f7c 100644
>> --- a/fs/f2fs/namei.c
>> +++ b/fs/f2fs/namei.c
>> @@ -246,7 +246,7 @@ int f2fs_update_extension_list(struct f2fs_sb_info *sbi, const char *name,
>>   		return -EINVAL;
>>   
>>   	if (hot) {
>> -		strncpy(extlist[count], name, strlen(name));
>> +		memcpy(extlist[count], name, strlen(name));
> 
> How about replacing with strcpy(extlist[count], name)? Because name length has
> already been checked before f2fs_update_extension_list, it should be valid, and
> will not cause overflow during copying.
> 

Your call; feel free to submit an alternative. Since it is different files, static
analysis might not know and complain, though. You might want to make sure that this
doesn't happen, and also add a comment explaining the reason for using strcpy().

Thanks,
Guenter