usbip: Fix misuse of strncpy()

[Shuah Khan <shuah@kernel.org>]

On 07/26/2018 04:39 AM, Ben Hutchings wrote:
> On Tue, 2018-07-24 at 11:04 -0600, Shuah Khan wrote:
>> On 07/20/2018 08:12 PM, Ben Hutchings wrote:
>>> gcc 8 reports:
>>>
>>> usbip_device_driver.c: In function ‘read_usb_vudc_device’:
>>> usbip_device_driver.c:106:2: error: ‘strncpy’ specified bound 256 equals destination size [-Werror=stringop-truncation]
>>>   strncpy(dev->path, path, SYSFS_PATH_MAX);
>>>   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>> usbip_device_driver.c:125:2: error: ‘strncpy’ specified bound 32 equals destination size [-Werror=stringop-truncation]
>>>   strncpy(dev->busid, name, SYSFS_BUS_ID_SIZE);
>>>   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>>
>>> I'm not convinced it makes sense to truncate the copied strings here,
>>> but since we're already doing so let's ensure they're still null-
>>> terminated.  We can't easily use strlcpy() here, so use snprintf().
>>>
>>> usbip_common.c has the same problem.
>>>
>>> Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
>>> Cc: stable@vger.kernel.org
>>> ---
>>>  tools/usb/usbip/libsrc/usbip_common.c        |    4 ++--
>>>  tools/usb/usbip/libsrc/usbip_device_driver.c |    4 ++--
>>>  2 files changed, 4 insertions(+), 4 deletions(-)
>>>
>>> --- a/tools/usb/usbip/libsrc/usbip_common.c
>>> +++ b/tools/usb/usbip/libsrc/usbip_common.c
>>> @@ -226,8 +226,8 @@ int read_usb_device(struct udev_device *
>>>  	path = udev_device_get_syspath(sdev);
>>>  	name = udev_device_get_sysname(sdev);
>>>  
>>> -	strncpy(udev->path,  path,  SYSFS_PATH_MAX);
>>> -	strncpy(udev->busid, name, SYSFS_BUS_ID_SIZE);
>>> +	snprintf(udev->path, SYSFS_PATH_MAX, "%s", path);
>>> +	snprintf(udev->busid, SYSFS_BUS_ID_SIZE, "%s", name);
>>
>> I am okay with the change to use snprintf(). Please add check for
>> return to avoid GCC 7 -Wformat-overflow wanrs on snprintf instances
>> that don't check return.
> [...]
> 
> I've tried running:
> 
> ./autogen.sh
> CC=gcc-7 CFLAGS=-Wformat-overflow ./configure 
> make
> 
> but this didn't produce any warnings.  How did you get the warning?
> 
> Ben.
> 

Sorry for the delay. It has been a busy few weeks with travel both
vacation and business.

Okay. Please check the e5dfa3f902b9a642ae8c6997d57d7c41e384a90b for
details. I didn't see this problem myself, likely because I was using
older gcc.

thanks,
-- Shuah

thanks,
-- Shuah
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