[SCSI] Fix issue reported by coverity in drivers/scsi/scsi_ioctl.c

This patch attempts to fix an issue found in drivers/scsi/scsi_ioctl.c by Coverity.

Error reported:
CID: 3437
Checker: FORWARD_NULL (help)
File: /export2/p4-coverity/mc2/linux26/drivers/scsi/scsi_ioctl.c
Function: scsi_ioctl_send_command
Description: Variable "buf" tracked as NULL was passed to a function that dereferences it.

Patch description:
buf can be NULL if inlen and outlen are both 0. This patch adds check if the
length is non-zero before calling copy from/to user.
Signed-off-by: Jayachandran C. <c.jayachandran@gmail.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>

drivers/scsi/scsi_ioctl.c

@@ -278,7 +278,7 @@ int scsi_ioctl_send_command(struct scsi_device *sdev,
 	 * Obtain the data to be sent to the device (if any).
 	 */
 
-	if(copy_from_user(buf, cmd_in + cmdlen, inlen))
+	if(inlen && copy_from_user(buf, cmd_in + cmdlen, inlen))
 		goto error;
 
 	switch (opcode) {
@@ -322,7 +322,7 @@ int scsi_ioctl_send_command(struct scsi_device *sdev,
 		if (copy_to_user(cmd_in, sense, sb_len))
 			result = -EFAULT;
 	} else {
-		if (copy_to_user(cmd_in, buf, outlen))
+		if (outlen && copy_to_user(cmd_in, buf, outlen))
 			result = -EFAULT;
 	}