2020-08-22 22:27:16

by Tom Rix

Subject: [PATCH] usb: storage: initialize variable

From: Tom Rix <[email protected]>

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 <[email protected]>
---
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) {
--
2.18.1

2020-08-23 01:13:10

by Alan Stern

Subject: Re: [PATCH] usb: storage: initialize variable

On Sat, Aug 22, 2020 at 02:18:39PM -0700, [email protected] wrote:
> From: Tom Rix <[email protected]>
>
> 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 <[email protected]>
> ---
> 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.

Alan Stern

2020-08-24 13:17:04

by Tom Rix

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, [email protected] wrote:
>> From: Tom Rix <[email protected]>
>>
>> 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 <[email protected]>
>> ---
>> 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
>