Re: drivers/net/can/usb/peak_usb/pcan_usb.c:523 pcan_usb_decode_error() error: we previously assumed 'cf' could be null (see line 503)

From: Marc Kleine-Budde
Date: Fri Dec 03 2021 - 09:59:12 EST

On 03.12.2021 17:09:55, Dan Carpenter wrote:
> tree: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> head: 58e1100fdc5990b0cc0d4beaf2562a92e621ac7d
> commit: c11dcee758302702a83c6e85e4c4c3d9af42d2b3 can: peak_usb: pcan_usb_decode_error(): upgrade handling of bus state changes
> config: x86_64-randconfig-m001-20211202 (https://download.01.org/0day-ci/archive/20211202/202112021833.wABxM5UN-lkp@xxxxxxxxx/config)
> compiler: gcc-9 (Debian 9.3.0-22) 9.3.0
>
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kernel test robot <lkp@xxxxxxxxx>
> Reported-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
>
> smatch warnings:
> drivers/net/can/usb/peak_usb/pcan_usb.c:523 pcan_usb_decode_error() error: we previously assumed 'cf' could be null (see line 503)
>
> vim +/cf +523 drivers/net/can/usb/peak_usb/pcan_usb.c
>
> 46be265d338833 Stephane Grosjean 2012-03-02 450 static int pcan_usb_decode_error(struct pcan_usb_msg_context *mc, u8 n,
> 46be265d338833 Stephane Grosjean 2012-03-02 451 u8 status_len)
> 46be265d338833 Stephane Grosjean 2012-03-02 452 {
> 46be265d338833 Stephane Grosjean 2012-03-02 453 struct sk_buff *skb;
> 46be265d338833 Stephane Grosjean 2012-03-02 454 struct can_frame *cf;
> c11dcee7583027 Stephane Grosjean 2021-07-15 455 enum can_state new_state = CAN_STATE_ERROR_ACTIVE;
> 46be265d338833 Stephane Grosjean 2012-03-02 456
> 46be265d338833 Stephane Grosjean 2012-03-02 457 /* ignore this error until 1st ts received */
> 46be265d338833 Stephane Grosjean 2012-03-02 458 if (n == PCAN_USB_ERROR_QOVR)
> 46be265d338833 Stephane Grosjean 2012-03-02 459 if (!mc->pdev->time_ref.tick_count)
> 46be265d338833 Stephane Grosjean 2012-03-02 460 return 0;
> 46be265d338833 Stephane Grosjean 2012-03-02 461
> c11dcee7583027 Stephane Grosjean 2021-07-15 462 /* allocate an skb to store the error frame */
> c11dcee7583027 Stephane Grosjean 2021-07-15 463 skb = alloc_can_err_skb(mc->netdev, &cf);

alloc_can_err_skb() ->
alloc_canfd_skb()

https://elixir.bootlin.com/linux/v5.15/source/drivers/net/can/dev/skb.c#L210

If skb is NULL, cf is set to NULL, too.

> 46be265d338833 Stephane Grosjean 2012-03-02 464
> c11dcee7583027 Stephane Grosjean 2021-07-15 465 if (n & PCAN_USB_ERROR_RXQOVR) {
> c11dcee7583027 Stephane Grosjean 2021-07-15 466 /* data overrun interrupt */
> c11dcee7583027 Stephane Grosjean 2021-07-15 467 netdev_dbg(mc->netdev, "data overrun interrupt\n");
> c11dcee7583027 Stephane Grosjean 2021-07-15 468 mc->netdev->stats.rx_over_errors++;
> c11dcee7583027 Stephane Grosjean 2021-07-15 469 mc->netdev->stats.rx_errors++;
> c11dcee7583027 Stephane Grosjean 2021-07-15 470 if (cf) {
>
> Check for NULL
>
> c11dcee7583027 Stephane Grosjean 2021-07-15 471 cf->can_id |= CAN_ERR_CRTL;
> c11dcee7583027 Stephane Grosjean 2021-07-15 472 cf->data[1] |= CAN_ERR_CRTL_RX_OVERFLOW;
> 46be265d338833 Stephane Grosjean 2012-03-02 473 }
> 46be265d338833 Stephane Grosjean 2012-03-02 474 }
> 46be265d338833 Stephane Grosjean 2012-03-02 475
> c11dcee7583027 Stephane Grosjean 2021-07-15 476 if (n & PCAN_USB_ERROR_TXQFULL)
> c11dcee7583027 Stephane Grosjean 2021-07-15 477 netdev_dbg(mc->netdev, "device Tx queue full)\n");
> c11dcee7583027 Stephane Grosjean 2021-07-15 478
> 46be265d338833 Stephane Grosjean 2012-03-02 479 if (n & PCAN_USB_ERROR_BUS_OFF) {
> 46be265d338833 Stephane Grosjean 2012-03-02 480 new_state = CAN_STATE_BUS_OFF;
> c11dcee7583027 Stephane Grosjean 2021-07-15 481 } else if (n & PCAN_USB_ERROR_BUS_HEAVY) {
> c11dcee7583027 Stephane Grosjean 2021-07-15 482 new_state = ((mc->pdev->bec.txerr >= 128) ||
> c11dcee7583027 Stephane Grosjean 2021-07-15 483 (mc->pdev->bec.rxerr >= 128)) ?
> c11dcee7583027 Stephane Grosjean 2021-07-15 484 CAN_STATE_ERROR_PASSIVE :
> c11dcee7583027 Stephane Grosjean 2021-07-15 485 CAN_STATE_ERROR_WARNING;
> c11dcee7583027 Stephane Grosjean 2021-07-15 486 } else {
> c11dcee7583027 Stephane Grosjean 2021-07-15 487 new_state = CAN_STATE_ERROR_ACTIVE;
> 46be265d338833 Stephane Grosjean 2012-03-02 488 }
> 46be265d338833 Stephane Grosjean 2012-03-02 489
> c11dcee7583027 Stephane Grosjean 2021-07-15 490 /* handle change of state */
> c11dcee7583027 Stephane Grosjean 2021-07-15 491 if (new_state != mc->pdev->dev.can.state) {
> c11dcee7583027 Stephane Grosjean 2021-07-15 492 enum can_state tx_state =
> c11dcee7583027 Stephane Grosjean 2021-07-15 493 (mc->pdev->bec.txerr >= mc->pdev->bec.rxerr) ?
> c11dcee7583027 Stephane Grosjean 2021-07-15 494 new_state : 0;
> c11dcee7583027 Stephane Grosjean 2021-07-15 495 enum can_state rx_state =
> c11dcee7583027 Stephane Grosjean 2021-07-15 496 (mc->pdev->bec.txerr <= mc->pdev->bec.rxerr) ?
> c11dcee7583027 Stephane Grosjean 2021-07-15 497 new_state : 0;
> 46be265d338833 Stephane Grosjean 2012-03-02 498
> c11dcee7583027 Stephane Grosjean 2021-07-15 499 can_change_state(mc->netdev, cf, tx_state, rx_state);
> 46be265d338833 Stephane Grosjean 2012-03-02 500
> c11dcee7583027 Stephane Grosjean 2021-07-15 501 if (new_state == CAN_STATE_BUS_OFF) {
> 46be265d338833 Stephane Grosjean 2012-03-02 502 can_bus_off(mc->netdev);
> c11dcee7583027 Stephane Grosjean 2021-07-15 @503 } else if (cf && (cf->can_id & CAN_ERR_CRTL)) {
>
> Check for NULL
>
> c11dcee7583027 Stephane Grosjean 2021-07-15 504 /* Supply TX/RX error counters in case of
> c11dcee7583027 Stephane Grosjean 2021-07-15 505 * controller error.
> c11dcee7583027 Stephane Grosjean 2021-07-15 506 */
> ea8b33bde76c8f Stephane Grosjean 2019-12-06 507 cf->data[6] = mc->pdev->bec.txerr;
> ea8b33bde76c8f Stephane Grosjean 2019-12-06 508 cf->data[7] = mc->pdev->bec.rxerr;
> ea8b33bde76c8f Stephane Grosjean 2019-12-06 509 }
> 46be265d338833 Stephane Grosjean 2012-03-02 510 }
> 46be265d338833 Stephane Grosjean 2012-03-02 511
> c11dcee7583027 Stephane Grosjean 2021-07-15 512 if (!skb)
> c11dcee7583027 Stephane Grosjean 2021-07-15 513 return -ENOMEM;

If cf is NULL, so is skb....

> 46be265d338833 Stephane Grosjean 2012-03-02 514
> 46be265d338833 Stephane Grosjean 2012-03-02 515 if (status_len & PCAN_USB_STATUSLEN_TIMESTAMP) {
> c9faaa09e2a133 Oliver Hartkopp 2012-11-21 516 struct skb_shared_hwtstamps *hwts = skb_hwtstamps(skb);
> c9faaa09e2a133 Oliver Hartkopp 2012-11-21 517
> d5888a1e75c799 Arnd Bergmann 2017-11-03 518 peak_usb_get_ts_time(&mc->pdev->time_ref, mc->ts16,
> d5888a1e75c799 Arnd Bergmann 2017-11-03 519 &hwts->hwtstamp);
> 46be265d338833 Stephane Grosjean 2012-03-02 520 }
> 46be265d338833 Stephane Grosjean 2012-03-02 521
> 46be265d338833 Stephane Grosjean 2012-03-02 522 mc->netdev->stats.rx_packets++;
> c7b74967799b1a Oliver Hartkopp 2020-11-20 @523 mc->netdev->stats.rx_bytes += cf->len;
> ^^^^^^^^
> No check for NULL.

...then this code is not reached.

Marc

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