can: ctucanfd: handle skb allocation failure

commit 9bd2492 upstream.

If skb allocation fails, the pointer to struct can_frame is NULL. This
is actually handled everywhere inside ctucan_err_interrupt() except for
the only place.

Add the missed NULL check.

Found by Linux Verification Center (linuxtesting.org) with SVACE static
analysis tool.

Fixes: 2dcb8e8 ("can: ctucanfd: add support for CTU CAN FD open-source IP core - bus independent part.")
Cc: stable@vger.kernel.org
Signed-off-by: Fedor Pchelkin <pchelkin@ispras.ru>
Acked-by: Pavel Pisa <pisa@cmp.felk.cvut.cz>
Reviewed-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Link: https://patch.msgid.link/20250114152138.139580-1-pchelkin@ispras.ru
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit b0e592dd46a0a952b41c3bf6c963afdd6a42b526)
Signed-off-by: Jack Vogel <jack.vogel@oracle.com>

Author: pchelkin91

drivers/net/can/ctucanfd/ctucanfd_base.c

@@ -867,10 +867,12 @@ static void ctucan_err_interrupt(struct net_device *ndev, u32 isr)
 			}
 			break;
 		case CAN_STATE_ERROR_ACTIVE:
-			cf->can_id |= CAN_ERR_CNT;
-			cf->data[1] = CAN_ERR_CRTL_ACTIVE;
-			cf->data[6] = bec.txerr;
-			cf->data[7] = bec.rxerr;
+			if (skb) {
+				cf->can_id |= CAN_ERR_CNT;
+				cf->data[1] = CAN_ERR_CRTL_ACTIVE;
+				cf->data[6] = bec.txerr;
+				cf->data[7] = bec.rxerr;
+			}
 			break;
 		default:
 			netdev_warn(ndev, "unhandled error state (%d:%s)!\n",