[SCSI] sg.c: Fix bad error handling in

I got a NULL derefrence in cdev_del+1 when called from sg_remove. By looking at
the code of sg_add, sg_alloc and sg_remove (all in drivers/scsi/sg.c) I found
out that sg_add is calling sg_alloc but if it fails afterwards it does not
deallocate the space that was allocated in sg_alloc and the redundant entry has
NULL in cdev. When sg_remove is being called, it tries to perform cdev_del to
this NULL cdev and fails.
Signed-off-by: Ishai Rabinovitz <ishai@mellanox.co.il>
Acked-by: Douglas Gilbert <dougg@torque.net>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>

drivers/scsi/sg.c

@@ -1402,6 +1402,7 @@ sg_add(struct class_device *cl_dev, struct class_interface *cl_intf)
 	Sg_device *sdp = NULL;
 	struct cdev * cdev = NULL;
 	int error, k;
+	unsigned long iflags;
 
 	disk = alloc_disk(1);
 	if (!disk) {
@@ -1429,7 +1430,7 @@ sg_add(struct class_device *cl_dev, struct class_interface *cl_intf)
 
 	error = cdev_add(cdev, MKDEV(SCSI_GENERIC_MAJOR, k), 1);
 	if (error)
-		goto out;
+		goto cdev_add_err;
 
 	sdp->cdev = cdev;
 	if (sg_sysfs_valid) {
@@ -1456,6 +1457,13 @@ sg_add(struct class_device *cl_dev, struct class_interface *cl_intf)
 
 	return 0;
 
+cdev_add_err:
+	write_lock_irqsave(&sg_dev_arr_lock, iflags);
+	kfree(sg_dev_arr[k]);
+	sg_dev_arr[k] = NULL;
+	sg_nr_dev--;
+	write_unlock_irqrestore(&sg_dev_arr_lock, iflags);
+
 out:
 	put_disk(disk);
 	if (cdev)