Re: [PATCH] Use strcmp instead of strncmp

[Marc Kleine-Budde <mkl@pengutronix.de>]

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On 11/14/2012 11:04 AM, Kurt Van Dijck wrote:
> On Wed, Nov 14, 2012 at 10:07:15AM +0100, Alexander Stein wrote:
>> Hello,
>>
>> On Wednesday 14 November 2012 09:55:37, Kurt Van Dijck wrote:
>>> On Tue, Nov 13, 2012 at 09:26:50PM +0100, Marc Kleine-Budde wrote:
>>>> On 11/13/2012 04:47 PM, Alexander Stein wrote:
>>>>> This bug was detected by the clang warning:
>>>>> libsocketcan.c:384:16: warning: argument to 'sizeof' in 'strncmp' call
>>>>> is the same expression as the source; did you mean to provide an
>>>>> explicit length? [-Wsizeof-pointer-memaccess]
>>>>> sizeof(name)) != 0)
>>>>> ~~~~~~~^~~~~~
>>> strlen() requires a null terminator. Is that always present?
>>> Unfortunately, I've no access to the libsocketcan code today...
>>>>>
>>>>> Signed-off-by: Alexander Stein <alexander.stein@systec-electronic.com>
>>>>> ---
>>>>>  src/libsocketcan.c |    3 ++-
>>>>>  1 files changed, 2 insertions(+), 1 deletions(-)
>>>>>
>>>>> diff --git a/src/libsocketcan.c b/src/libsocketcan.c
>>>>> index fedcbdc..3ad2a6c 100644
>>>>> --- a/src/libsocketcan.c
>>>>> +++ b/src/libsocketcan.c
>>>>> @@ -364,6 +364,7 @@ static int do_get_nl_link(int fd, __u8 acquire, 
>> const char *name, void *res)
>>>>>  		     nl_msg = NLMSG_NEXT(nl_msg, u_msglen)) {
>>>>>  			int type = nl_msg->nlmsg_type;
>>>>>  			int len;
>>>>> +			int namelen = strlen(name);
>>>>>  
>>>>>  			if (type == NLMSG_DONE) {
>>>>>  				done++;
>>>>> @@ -381,7 +382,7 @@ static int do_get_nl_link(int fd, __u8 acquire, 
>> const char *name, void *res)
>>>>>  
>>>>>  			if (strncmp
>>>>>  			    ((char *)RTA_DATA(tb[IFLA_IFNAME]), name,
>>>>> -			     sizeof(name)) != 0)
>>>>> +			     namelen) != 0)
>>>>
>>>> What about using strcmp() instead. AFAIK it will compare until it finds
>>>> the end of the string in one of the strings, so it should be no
>>>> difference here?
>>> if name contains a null terminator, using strcmp() is even better.
>>
>> name is passed directly from public API functions like can_get_state. So the 
>> user has to provide the null terminator. As this cannot be garuanteed 
> I think we should assume that the user passes a null terminated string.
> Otherwise, we must question if the user passes a valid address. I don't
> like to go that way.
> 
> strcmp() will just work.

+1

Marc

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