linux-kernel - Re: [PATCH] usb: storage: initialize variable

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Message-ID: <34834bbc-12e5-3fe1-7bb3-7a4c03acb03f@redhat.com>
Date:   Mon, 24 Aug 2020 06:13:09 -0700
From:   Tom Rix <trix@...hat.com>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     gregkh@...uxfoundation.org, linux-usb@...r.kernel.org,
        usb-storage@...ts.one-eyed-alien.net, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usb: storage: initialize variable


On 8/22/20 5:49 PM, Alan Stern wrote:
> On Sat, Aug 22, 2020 at 02:18:39PM -0700, trix@...hat.com wrote:
>> From: Tom Rix <trix@...hat.com>
>>
>> clang static analysis reports this representative problem
>>
>> transport.c:495:15: warning: Assigned value is garbage or
>>   undefined
>>         length_left -= partial;
>>                    ^  ~~~~~~~
>> partial is set only when usb_stor_bulk_transfer_sglist()
>> is successful.
>>
>> So initialize to partial to 0.
>>
>> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
>> Signed-off-by: Tom Rix <trix@...hat.com>
>> ---
>>  drivers/usb/storage/transport.c | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/usb/storage/transport.c b/drivers/usb/storage/transport.c
>> index 238a8088e17f..ce920851b1f2 100644
>> --- a/drivers/usb/storage/transport.c
>> +++ b/drivers/usb/storage/transport.c
>> @@ -461,7 +461,7 @@ static int usb_stor_bulk_transfer_sglist(struct us_data *us, unsigned int pipe,
>>  int usb_stor_bulk_srb(struct us_data* us, unsigned int pipe,
>>  		      struct scsi_cmnd* srb)
>>  {
>> -	unsigned int partial;
>> +	unsigned int partial = 0;
>>  	int result = usb_stor_bulk_transfer_sglist(us, pipe, scsi_sglist(srb),
>>  				      scsi_sg_count(srb), scsi_bufflen(srb),
>>  				      &partial);
>> @@ -484,7 +484,7 @@ int usb_stor_bulk_transfer_sg(struct us_data* us, unsigned int pipe,
>>  		void *buf, unsigned int length_left, int use_sg, int *residual)
>>  {
>>  	int result;
>> -	unsigned int partial;
>> +	unsigned int partial = 0;
>>  
>>  	/* are we scatter-gathering? */
>>  	if (use_sg) {
> Yes, this is a bug.  But the right way to fix it is to change 
> usb_stor_bulk_transfer_sglist(): Make it store 0 to *act_len at the 
> start.
>
> That way you change only one localized piece of code, instead of 
> changing multiple callers and leaving a possibility of more errors being 
> added in the future.

I'll respin the patch.

It will exchange the compile time initialization fix for a run time if-check fix.

> Alan Stern
>