On Tue, Aug 15, 2017 at 12:00 PM, Oleksandr Shamray
[off-list ref] wrote:

+       case JTAG_IOCXFER:
+               if (copy_from_user(&xfer, varg, sizeof(struct jtag_xfer)))
+                       return -EFAULT;
+
+               if (xfer.length >= JTAG_MAX_XFER_DATA_LEN)
+                       return -EFAULT;
+
+               user_tdio_data = xfer.tdio;
+               xfer.tdio = jtag_copy_from_user((void __user *)user_tdio_data,
+                                               xfer.length);
+               if (!xfer.tdio)
+                       return -ENOMEM;

This is not safe for 32-bit processes on 64-bit kernels, since the
structure layout differs for the pointer member. It's better to always
use either rework the structure to avoid the pointer, or to use a
__u64 member to store it, and then use u64_to_user_ptr()
to convert it in the kernel.

+       case JTAG_GIOCSTATUS:
+               if (jtag->ops->status_get)
+                       err = jtag->ops->status_get(jtag,
+                                               (enum jtag_endstate *)&value);

This pointer cast is also not safe, as an enum might have a different
size than the 'value' variable that is not an enum. I think you need to
change the argument type for the callback, or maybe use another
intermediate.

+static int jtag_open(struct inode *inode, struct file *file)
+{
+       struct jtag *jtag = container_of(inode->i_cdev, struct jtag, cdev);
+
+       spin_lock(&jtag->lock);
+
+       if (jtag->is_open) {
+               dev_info(NULL, "jtag already opened\n");
+               spin_unlock(&jtag->lock);
+               return -EBUSY;
+       }
+
+       jtag->is_open = true;
+       file->private_data = jtag;
+       spin_unlock(&jtag->lock);
+       return 0;
+}

Does the 'is_open' flag protect you from something that doesn't
also happen after a 'dup()' call on the file descriptor?

+ * @mode: access mode
+ * @type: transfer type
+ * @direction: xfer direction
+ * @length: xfer bits len
+ * @tdio : xfer data array
+ * @endir: xfer end state
+ *
+ * Structure represents interface to Aspeed JTAG device for jtag sdr xfer
+ * execution.
+ */
+struct jtag_xfer {
+       __u8    mode;
+       __u8    type;
+       __u8    direction;
+       __u32   length;
+       __u8    *tdio;
+       __u8    endstate;
+};

As mentioned above, the pointer in here makes it incompatible. Also,
you should reorder the members to avoid the implied padding.
Moving the 'endstate' before 'length' is sufficient.

        Arnd