linux-kernel - Re: [PATCH v2 3/4] fs: unicode: Use strscpy() instead of strncpy()

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Date:   Fri, 19 Mar 2021 16:02:05 +0530
From:   Shreeya Patel <shreeya.patel@...labora.com>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     krisman@...labora.com, jaegeuk@...nel.org, yuchao0@...wei.com,
        tytso@....edu, adilger.kernel@...ger.ca, drosen@...gle.com,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        kernel@...labora.com, andre.almeida@...labora.com,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCH v2 3/4] fs: unicode: Use strscpy() instead of strncpy()


On 19/03/21 2:33 am, Eric Biggers wrote:
> On Thu, Mar 18, 2021 at 07:03:04PM +0530, Shreeya Patel wrote:
>> Following warning was reported by Kernel Test Robot.
>>
>> In function 'utf8_parse_version',
>> inlined from 'utf8_load' at fs/unicode/utf8mod.c:195:7:
>>>> fs/unicode/utf8mod.c:175:2: warning: 'strncpy' specified bound 12 equals
>> destination size [-Wstringop-truncation]
>> 175 |  strncpy(version_string, version, sizeof(version_string));
>>      |  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>
>> The -Wstringop-truncation warning highlights the unintended
>> uses of the strncpy function that truncate the terminating NULL
>> character from the source string.
>> Unlike strncpy(), strscpy() always null-terminates the destination string,
>> hence use strscpy() instead of strncpy().
>>
>> Signed-off-by: Shreeya Patel <shreeya.patel@...labora.com>
>> Reported-by: kernel test robot <lkp@...el.com>
>> ---
>> Changes in v2
>>    - Resolve warning of -Wstringop-truncation reported by
>>      kernel test robot.
>>
>>   fs/unicode/unicode-core.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/fs/unicode/unicode-core.c b/fs/unicode/unicode-core.c
>> index d5f09e022ac5..287a8a48836c 100644
>> --- a/fs/unicode/unicode-core.c
>> +++ b/fs/unicode/unicode-core.c
>> @@ -179,7 +179,7 @@ static int unicode_parse_version(const char *version, unsigned int *maj,
>>   		{0, NULL}
>>   	};
>>   
>> -	strncpy(version_string, version, sizeof(version_string));
>> +	strscpy(version_string, version, sizeof(version_string));
>>   
> Shouldn't unicode_parse_version() return an error if the string gets truncated
> here?  I.e. check if strscpy() returns < 0.
>
> Also, this is a "fix" (though one that doesn't currently matter, since 'version'
> is currently always shorter than sizeof(version_string)), so it should go first
> in the series and have a Fixes tag.


Thanks Eric, will send v3 for it.

>
> - Eric