On Wed, 24 Sep 2014, Mark Knibbs wrote:
> Hi,
>
> This follows on from something I mentioned in my recent post "[PATCH]
> storage: Don't scan target 7 for SCM USB-SCSI converters".
>
> In drivers/usb/storage/usb.c, usb_stor_control_thread():
> /* reject if target != 0 or if LUN is higher than
> * the maximum known LUN
> */
> else if (us->srb->device->id &&
> !(us->fflags & US_FL_SCM_MULT_TARG)) {
> usb_stor_dbg(us, "Bad target number (%d:%llu)\n",
> us->srb->device->id,
> us->srb->device->lun);
> us->srb->result = DID_BAD_TARGET << 16;
> }
>
> else if (us->srb->device->lun > us->max_lun) {
> usb_stor_dbg(us, "Bad LUN (%d:%llu)\n",
> ...
>
> The condition (us->srb->device->id && !(us->fflags & US_FL_SCM_MULT_TARG))
> means:
> - If not SCM_MULT_TARG, reject if us->srb->device->id is non-zero. That
> works for the usual case.
> - If SCM_MULT_TARG, never reject. Hmm...
>
> Would it be better/clearer to change the condition to simply
> (us->srb->device->id >= host->max_id)
>
> Then the command is rejected if us->srb->device->id is too large, and works
> for the SCM_MULT_TARG case too. (host->max_id is 1 for the non-SCM_MULT_TARG
> case.) Plus the condition matches nicely with the later LUN check. Untested
> patch below.
>
>
> Signed-off-by: Mark Knibbs <ma...@clara.co.uk>
>
> diff -up linux-3.17-rc6/drivers/usb/storage/usb.c.orig
> linux-3.17-rc6/drivers/usb/storage/usb.c
> --- linux-3.17-rc6/drivers/usb/storage/usb.c.orig 2014-09-21
> 23:43:02.000000000 +0100
> +++ linux-3.17-rc6/drivers/usb/storage/usb.c 2014-09-24 13:09:55.000000000
> +0100
> @@ -342,11 +342,10 @@ static int usb_stor_control_thread(void
> us->srb->result = DID_ERROR << 16;
> }
>
> - /* reject if target != 0 or if LUN is higher than
> + /* reject if target is invalid or if LUN is higher than
> * the maximum known LUN
> */
> - else if (us->srb->device->id &&
> - !(us->fflags & US_FL_SCM_MULT_TARG)) {
> + else if (us->srb->device->id >= host->max_id) {
> usb_stor_dbg(us, "Bad target number (%d:%llu)\n",
> us->srb->device->id,
> us->srb->device->lun);
That's probably okay. As far as I know, the SCSI layer doesn't
generate commands for targets with id >= host->max_id, so this entire
test may be unnecessary.
Alan Stern
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