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SubjectRe: [PATCH] usb: storage: initialize variable
On Sat, Aug 22, 2020 at 02:18:39PM -0700, trix@redhat.com wrote:
> From: Tom Rix <trix@redhat.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@redhat.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.

Alan Stern

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