[U-Boot] [PATCH] drivers: usb: fsl: Fix NULL terminating issue for usb controller name string

[Marek Vasut]

On 06/02/2016 05:14 AM, Rajesh Bhagat wrote:
> 
> 
>> -----Original Message-----
>> From: Marek Vasut [mailto:marex at denx.de]
>> Sent: Thursday, June 02, 2016 1:38 AM
>> To: Rajesh Bhagat <rajesh.bhagat at nxp.com>; u-boot at lists.denx.de
>> Cc: york sun <york.sun at nxp.com>; Sriram Dash <sriram.dash at nxp.com>
>> Subject: Re: [PATCH] drivers: usb: fsl: Fix NULL terminating issue for usb controller
>> name string
>>
>> On 06/01/2016 04:55 PM, Rajesh Bhagat wrote:
>>>
>>>
>>>> -----Original Message-----
>>>> From: Marek Vasut [mailto:marex at denx.de]
>>>> Sent: Wednesday, June 01, 2016 6:51 PM
>>>> To: Rajesh Bhagat <rajesh.bhagat at nxp.com>; u-boot at lists.denx.de
>>>> Cc: york sun <york.sun at nxp.com>; Sriram Dash <sriram.dash at nxp.com>
>>>> Subject: Re: [PATCH] drivers: usb: fsl: Fix NULL terminating issue
>>>> for usb controller name string
>>>>
>>>> On 06/01/2016 01:17 PM, Rajesh Bhagat wrote:
>>>>> Fixes NULL terminating issue for usb controller name string and
>>>>> performs code cleanup for intializing variables
>>>>> current_usb_controller and usb_phy.
>>>>>
>>>>> Signed-off-by: Rajesh Bhagat <rajesh.bhagat at nxp.com>
>>>>> ---
>>>>>  drivers/usb/host/ehci-fsl.c |   10 ++++------
>>>>>  1 files changed, 4 insertions(+), 6 deletions(-)
>>>>>
>>>>> diff --git a/drivers/usb/host/ehci-fsl.c
>>>>> b/drivers/usb/host/ehci-fsl.c index a43d37d..a806993 100644
>>>>> --- a/drivers/usb/host/ehci-fsl.c
>>>>> +++ b/drivers/usb/host/ehci-fsl.c
>>>>> @@ -49,11 +49,9 @@ int ehci_hcd_init(int index, enum usb_init_type init,
>>>>>  	struct usb_ehci *ehci = NULL;
>>>>>  	const char *phy_type = NULL;
>>>>>  	size_t len;
>>>>> -	char current_usb_controller[5];
>>>>> +	char current_usb_controller[5] = {0};
>>>>>  #ifdef CONFIG_SYS_FSL_USB_INTERNAL_UTMI_PHY
>>>>> -	char usb_phy[5];
>>>>> -
>>>>> -	usb_phy[0] = '\0';
>>>>> +	char usb_phy[5] = {0};
>>>>>  #endif
>>>>>  	if (has_erratum_a007075()) {
>>>>>  		/*
>>>>> @@ -64,8 +62,8 @@ int ehci_hcd_init(int index, enum usb_init_type init,
>>>>>  		 */
>>>>>  		mdelay(5);
>>>>>  	}
>>>>> -	memset(current_usb_controller, '\0', 5);
>>>>> -	snprintf(current_usb_controller, 4, "usb%d", index+1);
>>>>> +	snprintf(current_usb_controller, sizeof(current_usb_controller),
>>>>> +		 "usb%d", index+1);
>>>>
>>>> What is the actual problem here ? snprintf() will add the \0 at the
>>>> end of the string, so I don't see any "null terminating issue" in the code.
>>>> I can understand using the sizeof() in the snprintf(), which is valid, but that's all.
>>>>
>>>
>>> Hello Marek,
>>>
>>> It is surprising for me too, but same can be verified even on x86
>>> machine using below test program, Can it be compiler optimization of memset?
>>
>> The man snprintf explains that:
>>
>>        int snprintf(char *str, size_t size, const char *format, ...);
>>
>>        The functions snprintf() and vsnprintf() write at most size bytes (including the
>> terminating null byte ('\0')) to str.
> 
> Hello Marek, 
> 
> You are right, snprintf does add a terminating null byte. Let me share details of issue faced: 
> 
> It indeed is not NULL terminating issue, as snprintf adds it. This issue is due to the length passed to 
> snprintf is causing the data loss of the last byte: 
> 
> Current code: snprintf(current_usb_controller, 4, "usb%d", index+1); <==== 4 is passed 
> Proposed code: snprintf(current_usb_controller, 5,"usb%d", index+1); i.e. sizeof(current_usb_controller) <== 5 is passed
> 
> Current code is copying 4 bytes i.e. "usb1" and snprintf adds '\0' at 4th offset which causes the data loss and final data
> Becomes "usb". But proposed code is copying 5 bytes i.e. "usb1\0" and snprintf adds '\0' at 5th offset and final data becomes
> "usb1" which is the expected output.

That's correct, thus you need to use the sizeof().

-- 
Best regards,
Marek Vasut