Re: [PATCH] usb: gadget: configfs: Fix OOB read on empty string write

[Xinyu Liu <1171169449@qq.com>]

Hi Sergey,

Thanks for your review.

You are right, removing the blank line is inappropriate. I’ve 
double-checked the original code and confirmed there are no invisible 
spaces or tabs, yet checkpatch.pl still reports "ERROR: trailing 
whitespace" on these lines. I removed the empty line here, and it 
resolved the error.

Thanks for pointing this out!

Best regards,
Xinyu Liu

在 2025/7/9 16:48, Sergey Shtylyov 写道:
> On 7/9/25 6:55 AM, Xinyu Liu wrote:
>
>> When writing an empty string to either 'qw_sign' or 'landingPage'
>> sysfs attributes, the store functions attempt to access page[l - 1]
>> before validating that the length 'l' is greater than zero.
>>
>> This patch fixes the vulnerability by adding a check at the beginning
>> of os_desc_qw_sign_store() and webusb_landingPage_store() to handle
>> the zero-length input case gracefully by returning immediately.
>>
>> Signed-off-by: Xinyu Liu <katieeliu@tencent.com>
>> ---
>>   drivers/usb/gadget/configfs.c | 6 ++++--
>>   1 file changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/usb/gadget/configfs.c b/drivers/usb/gadget/configfs.c
>> index fba2a56dae97..1bb32d6be9b3 100644
>> --- a/drivers/usb/gadget/configfs.c
>> +++ b/drivers/usb/gadget/configfs.c
>> @@ -1064,7 +1064,8 @@ static ssize_t webusb_landingPage_store(struct config_item *item, const char *pa
>>   	struct gadget_info *gi = webusb_item_to_gadget_info(item);
>>   	unsigned int bytes_to_strip = 0;
>>   	int l = len;
>> -
>     Why are you removing empty line here?
>
>> +	if (!len)
>> +		return len;
>>   	if (page[l - 1] == '\n') {
>>   		--l;
>>   		++bytes_to_strip;
>> @@ -1187,7 +1188,8 @@ static ssize_t os_desc_qw_sign_store(struct config_item *item, const char *page,
>>   {
>>   	struct gadget_info *gi = os_desc_item_to_gadget_info(item);
>>   	int res, l;
>> -
>     And here?
>
>> +	if (!len)
>> +		return len;
>>   	l = min_t(int, len, OS_STRING_QW_SIGN_LEN >> 1);
>>   	if (page[l - 1] == '\n')
>>   		--l;
> MBR, Sergey