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From:   Jia-Ju Bai <baijiaju1990@gmail.com>
To:     isdn@linux-pingi.de, davem@davemloft.net, pakki001@umn.edu,
        tranmanphong@gmail.com, gregkh@linuxfoundation.org,
        rfontana@redhat.com, gustavo@embeddedor.com, tglx@linutronix.de
Cc:     netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        Jia-Ju Bai <baijiaju1990@gmail.com>
Subject: [PATCH] isdn: mISDN: hfcsusb: Fix possible null-pointer dereferences in start_isoc_chain()
Date:   Fri, 26 Jul 2019 16:27:36 +0800
Message-Id: <20190726082736.8195-1-baijiaju1990@gmail.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

In start_isoc_chain(), usb_alloc_urb() on line 1392 may fail 
and return NULL. At this time, fifo->iso[i].urb is assigned to NULL.

Then, fifo->iso[i].urb is used at some places, such as:
LINE 1405:    fill_isoc_urb(fifo->iso[i].urb, ...)
                  urb->number_of_packets = num_packets;
                  urb->transfer_flags = URB_ISO_ASAP;
                  urb->actual_length = 0;
                  urb->interval = interval;
LINE 1416:    fifo->iso[i].urb->...
LINE 1419:    fifo->iso[i].urb->...

Thus, possible null-pointer dereferences may occur.

To fix these bugs, "continue" is added to avoid using fifo->iso[i].urb
when it is NULL.

These bugs are found by a static analysis tool STCheck written by us.

Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
---
 drivers/isdn/hardware/mISDN/hfcsusb.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/isdn/hardware/mISDN/hfcsusb.c b/drivers/isdn/hardware/mISDN/hfcsusb.c
index 0e224232f746..8fb7c5dea07f 100644
--- a/drivers/isdn/hardware/mISDN/hfcsusb.c
+++ b/drivers/isdn/hardware/mISDN/hfcsusb.c
@@ -1394,6 +1394,7 @@ start_isoc_chain(struct usb_fifo *fifo, int num_packets_per_urb,
 				printk(KERN_DEBUG
 				       "%s: %s: alloc urb for fifo %i failed",
 				       hw->name, __func__, fifo->fifonum);
+				continue;
 			}
 			fifo->iso[i].owner_fifo = (struct usb_fifo *) fifo;
 			fifo->iso[i].indx = i;
-- 
2.17.0