Re: Unitialized Variable and Null Pointer Dereference bug in gb_bootrom_get_firmware

[Dongliang Mu]

On Tue, Jun 21, 2022 at 10:55 PM Dan Carpenter <dan.carpenter@xxxxxxxxxx> wrote:
>
> On Tue, Jun 21, 2022 at 10:36:04PM +0800, Dongliang Mu wrote:
> > Hi maintainers,
> >
> > I would like to send one bug report.
> >
> > In gb_bootrom_get_firmware, if the first branch is satisfied, it will
> > go to queue_work, leading to the dereference of uninitialized const
> > variable "fw". If the second branch is satisfied, it will go to unlock
> > with fw as NULL pointer, leading to a NULL Pointer Dereference.
> >
> > The Fixes commit should be [1], introducing the dereference of "fw" in
> > the error handling code.
> >
> > I am not sure how to fix this bug. Any comment on removing the
> > dereference of fw?
> >
> > [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=a4293e1d4e6416477976ee3bd248589d3fc4bb19
>
> No, there is no bug there.  It is a static checker false positive.
>
> When you are reporting static checker warnings then please at least
> mention it is from static analsysis so we can know what we are dealing
> with.

Thanks Dan. I will do it next time.

I am just playing fun with the built-in coccinelle script. Static
analysis has many false positives. Sorry for my false alarm.

Thanks for your valuable feedback.

>
> Here is the code.
>
> drivers/staging/greybus/bootrom.c
>    241  static int gb_bootrom_get_firmware(struct gb_operation *op)
>    242  {
>    243          struct gb_bootrom *bootrom = gb_connection_get_data(op->connection);
>    244          const struct firmware *fw;
>                                       ^^^
>
>
>    245          struct gb_bootrom_get_firmware_request *firmware_request;
>    246          struct gb_bootrom_get_firmware_response *firmware_response;
>    247          struct device *dev = &op->connection->bundle->dev;
>    248          unsigned int offset, size;
>    249          enum next_request_type next_request;
>    250          int ret = 0;
>    251
>    252          /* Disable timeouts */
>    253          gb_bootrom_cancel_timeout(bootrom);
>    254
>    255          if (op->request->payload_size != sizeof(*firmware_request)) {
>    256                  dev_err(dev, "%s: Illegal size of get firmware request (%zu %zu)\n",
>    257                          __func__, op->request->payload_size,
>    258                          sizeof(*firmware_request));
>    259                  ret = -EINVAL;
>    260                  goto queue_work;
>
> "ret" is -EINVAL.  "fw" is uninitialized.
>
>    261          }
>    262
>    263          mutex_lock(&bootrom->mutex);
>    264
>    265          fw = bootrom->fw;
>    266          if (!fw) {
>    267                  dev_err(dev, "%s: firmware not available\n", __func__);
>    268                  ret = -EINVAL;
>    269                  goto unlock;
>
> "ret" is -EINVAL.  "fw" is NULL.
>
>    270          }
>    271
>
> For the rest "fw" is valid.
>
>    272          firmware_request = op->request->payload;
>    273          offset = le32_to_cpu(firmware_request->offset);
>    274          size = le32_to_cpu(firmware_request->size);
>    275
>    276          if (offset >= fw->size || size > fw->size - offset) {
>    277                  dev_warn(dev, "bad firmware request (offs = %u, size = %u)\n",
>    278                           offset, size);
>    279                  ret = -EINVAL;
>    280                  goto unlock;
>    281          }
>    282
>    283          if (!gb_operation_response_alloc(op, sizeof(*firmware_response) + size,
>    284                                           GFP_KERNEL)) {
>    285                  dev_err(dev, "%s: error allocating response\n", __func__);
>    286                  ret = -ENOMEM;
>    287                  goto unlock;
>    288          }
>    289
>    290          firmware_response = op->response->payload;
>    291          memcpy(firmware_response->data, fw->data + offset, size);
>    292
>    293          dev_dbg(dev, "responding with firmware (offs = %u, size = %u)\n",
>    294                  offset, size);
>    295
>    296  unlock:
>    297          mutex_unlock(&bootrom->mutex);
>    298
>    299  queue_work:
>    300          /* Refresh timeout */
>    301          if (!ret && (offset + size == fw->size))
>                     ^^^^^
> The "!ret" is only true when "fw" is valid.
>
>
>    302                  next_request = NEXT_REQ_READY_TO_BOOT;
>    303          else
>    304                  next_request = NEXT_REQ_GET_FIRMWARE;
>    305
>    306          gb_bootrom_set_timeout(bootrom, next_request, NEXT_REQ_TIMEOUT_MS);
>    307
>    308          return ret;
>    309  }
>
> regards,
> dan carpenter
>