sg_ioctl(struct file *filp, unsigned int cmd_in, unsigned long arg)
{
	void __user *p = (void __user *)arg;
	int __user *ip = p;
	int result, val, read_only;
	Sg_device *sdp;
	Sg_fd *sfp;
	Sg_request *srp;
	unsigned long iflags;

	if ((!(sfp = (Sg_fd *) filp->private_data)) || (!(sdp = sfp->parentdp)))
		return -ENXIO;

	SCSI_LOG_TIMEOUT(3, sg_printk(KERN_INFO, sdp,
				   "sg_ioctl: cmd=0x%x\n", (int) cmd_in));
	read_only = (O_RDWR != (filp->f_flags & O_ACCMODE));

	switch (cmd_in) {
	case SG_IO:
		if (atomic_read(&sdp->detaching))
			return -ENODEV;
		if (!scsi_block_when_processing_errors(sdp->device))
			return -ENXIO;
		if (!access_ok(VERIFY_WRITE, p, SZ_SG_IO_HDR))
			return -EFAULT;
		result = sg_new_write(sfp, filp, p, SZ_SG_IO_HDR,
				 1, read_only, 1, &srp);
		if (result < 0)
			return result;
		result = wait_event_interruptible(sfp->read_wait,
			(srp_done(sfp, srp) || atomic_read(&sdp->detaching)));
		if (atomic_read(&sdp->detaching))
			return -ENODEV;
		write_lock_irq(&sfp->rq_list_lock);
		if (srp->done) {
			srp->done = 2;
			write_unlock_irq(&sfp->rq_list_lock);
			result = sg_new_read(sfp, p, SZ_SG_IO_HDR, srp);
			return (result < 0) ? result : 0;
		}
		srp->orphan = 1;
		write_unlock_irq(&sfp->rq_list_lock);
		return result;	/* -ERESTARTSYS because signal hit process */
	case SG_SET_TIMEOUT:
		result = get_user(val, ip);
		if (result)
			return result;
		if (val < 0)
			return -EIO;
		if (val >= mult_frac((s64)INT_MAX, USER_HZ, HZ))
			val = min_t(s64, mult_frac((s64)INT_MAX, USER_HZ, HZ),
				    INT_MAX);
		sfp->timeout_user = val;
		sfp->timeout = mult_frac(val, HZ, USER_HZ);

		return 0;
	case SG_GET_TIMEOUT:	/* N.B. User receives timeout as return value */
				/* strange ..., for backward compatibility */
		return sfp->timeout_user;
	case SG_SET_FORCE_LOW_DMA:
		result = get_user(val, ip);
		if (result)
			return result;
		if (val) {
			sfp->low_dma = 1;
			if ((0 == sfp->low_dma) && (0 == sg_res_in_use(sfp))) {
				val = (int) sfp->reserve.bufflen;
				sg_remove_scat(sfp, &sfp->reserve);
				sg_build_reserve(sfp, val);
			}
		} else {
			if (atomic_read(&sdp->detaching))
				return -ENODEV;
			sfp->low_dma = sdp->device->host->unchecked_isa_dma;
		}
		return 0;
	case SG_GET_LOW_DMA:
		return put_user((int) sfp->low_dma, ip);
	case SG_GET_SCSI_ID:
		if (!access_ok(VERIFY_WRITE, p, sizeof (sg_scsi_id_t)))
			return -EFAULT;
		else {
			sg_scsi_id_t __user *sg_idp = p;

			if (atomic_read(&sdp->detaching))
				return -ENODEV;
			__put_user((int) sdp->device->host->host_no,
				   &sg_idp->host_no);
			__put_user((int) sdp->device->channel,
				   &sg_idp->channel);
			__put_user((int) sdp->device->id, &sg_idp->scsi_id);
			__put_user((int) sdp->device->lun, &sg_idp->lun);
			__put_user((int) sdp->device->type, &sg_idp->scsi_type);
			__put_user((short) sdp->device->host->cmd_per_lun,
				   &sg_idp->h_cmd_per_lun);
			__put_user((short) sdp->device->queue_depth,
				   &sg_idp->d_queue_depth);
			__put_user(0, &sg_idp->unused[0]);
			__put_user(0, &sg_idp->unused[1]);
			return 0;
		}
	case SG_SET_FORCE_PACK_ID:
		result = get_user(val, ip);
		if (result)
			return result;
		sfp->force_packid = val ? 1 : 0;
		return 0;
	case SG_GET_PACK_ID:
		if (!access_ok(VERIFY_WRITE, ip, sizeof (int)))
			return -EFAULT;
		read_lock_irqsave(&sfp->rq_list_lock, iflags);
		for (srp = sfp->headrp; srp; srp = srp->nextrp) {
			if ((1 == srp->done) && (!srp->sg_io_owned)) {
				read_unlock_irqrestore(&sfp->rq_list_lock,
						       iflags);
				__put_user(srp->header.pack_id, ip);
				return 0;
			}
		}
		read_unlock_irqrestore(&sfp->rq_list_lock, iflags);
		__put_user(-1, ip);
		return 0;
	case SG_GET_NUM_WAITING:
		read_lock_irqsave(&sfp->rq_list_lock, iflags);
		for (val = 0, srp = sfp->headrp; srp; srp = srp->nextrp) {
			if ((1 == srp->done) && (!srp->sg_io_owned))
				++val;
		}
		read_unlock_irqrestore(&sfp->rq_list_lock, iflags);
		return put_user(val, ip);
	case SG_GET_SG_TABLESIZE:
		return put_user(sdp->sg_tablesize, ip);
	case SG_SET_RESERVED_SIZE:
		result = get_user(val, ip);
		if (result)
			return result;
                if (val < 0)
                        return -EINVAL;
		val = min_t(int, val,
			    max_sectors_bytes(sdp->device->request_queue));
		if (val != sfp->reserve.bufflen) {
			if (sg_res_in_use(sfp) || sfp->mmap_called)
				return -EBUSY;
			sg_remove_scat(sfp, &sfp->reserve);
			sg_build_reserve(sfp, val);
		}
		return 0;
	case SG_GET_RESERVED_SIZE:
		val = min_t(int, sfp->reserve.bufflen,
			    max_sectors_bytes(sdp->device->request_queue));
		return put_user(val, ip);
	case SG_SET_COMMAND_Q:
		result = get_user(val, ip);
		if (result)
			return result;
		sfp->cmd_q = val ? 1 : 0;
		return 0;
	case SG_GET_COMMAND_Q:
		return put_user((int) sfp->cmd_q, ip);
	case SG_SET_KEEP_ORPHAN:
		result = get_user(val, ip);
		if (result)
			return result;
		sfp->keep_orphan = val;
		return 0;
	case SG_GET_KEEP_ORPHAN:
		return put_user((int) sfp->keep_orphan, ip);
	case SG_NEXT_CMD_LEN:
		result = get_user(val, ip);
		if (result)
			return result;
		sfp->next_cmd_len = (val > 0) ? val : 0;
		return 0;
	case SG_GET_VERSION_NUM:
		return put_user(sg_version_num, ip);
	case SG_GET_ACCESS_COUNT:
		/* faked - we don't have a real access count anymore */
		val = (sdp->device ? 1 : 0);
		return put_user(val, ip);
	case SG_GET_REQUEST_TABLE:
		if (!access_ok(VERIFY_WRITE, p, SZ_SG_REQ_INFO * SG_MAX_QUEUE))
			return -EFAULT;
		else {
			sg_req_info_t *rinfo;
			unsigned int ms;

			rinfo = kmalloc(SZ_SG_REQ_INFO * SG_MAX_QUEUE,
								GFP_KERNEL);
			if (!rinfo)
				return -ENOMEM;
			read_lock_irqsave(&sfp->rq_list_lock, iflags);
			for (srp = sfp->headrp, val = 0; val < SG_MAX_QUEUE;
			     ++val, srp = srp ? srp->nextrp : srp) {
				memset(&rinfo[val], 0, SZ_SG_REQ_INFO);
				if (srp) {
					rinfo[val].req_state = srp->done + 1;
					rinfo[val].problem =
					    srp->header.masked_status & 
					    srp->header.host_status & 
					    srp->header.driver_status;
					if (srp->done)
						rinfo[val].duration =
							srp->header.duration;
					else {
						ms = jiffies_to_msecs(jiffies);
						rinfo[val].duration =
						    (ms > srp->header.duration) ?
						    (ms - srp->header.duration) : 0;
					}
					rinfo[val].orphan = srp->orphan;
					rinfo[val].sg_io_owned =
							srp->sg_io_owned;
					rinfo[val].pack_id =
							srp->header.pack_id;
					rinfo[val].usr_ptr =
							srp->header.usr_ptr;
				}
			}
			read_unlock_irqrestore(&sfp->rq_list_lock, iflags);
			result = __copy_to_user(p, rinfo, 
						SZ_SG_REQ_INFO * SG_MAX_QUEUE);
			result = result ? -EFAULT : 0;
			kfree(rinfo);
			return result;
		}
	case SG_EMULATED_HOST:
		if (atomic_read(&sdp->detaching))
			return -ENODEV;
		return put_user(sdp->device->host->hostt->emulated, ip);
	case SCSI_IOCTL_SEND_COMMAND:
		if (atomic_read(&sdp->detaching))
			return -ENODEV;
		if (read_only) {
			unsigned char opcode = WRITE_6;
			Scsi_Ioctl_Command __user *siocp = p;

			if (copy_from_user(&opcode, siocp->data, 1))
				return -EFAULT;
			if (sg_allow_access(filp, &opcode))
				return -EPERM;
		}
		return sg_scsi_ioctl(sdp->device->request_queue, NULL, filp->f_mode, p);
	case SG_SET_DEBUG:
		result = get_user(val, ip);
		if (result)
			return result;
		sdp->sgdebug = (char) val;
		return 0;
	case BLKSECTGET:
		return put_user(max_sectors_bytes(sdp->device->request_queue),
				ip);
	case BLKTRACESETUP:
		return blk_trace_setup(sdp->device->request_queue,
				       sdp->disk->disk_name,
				       MKDEV(SCSI_GENERIC_MAJOR, sdp->index),
				       NULL,
				       (char *)arg);
	case BLKTRACESTART:
		return blk_trace_startstop(sdp->device->request_queue, 1);
	case BLKTRACESTOP:
		return blk_trace_startstop(sdp->device->request_queue, 0);
	case BLKTRACETEARDOWN:
		return blk_trace_remove(sdp->device->request_queue);
	case SCSI_IOCTL_GET_IDLUN:
	case SCSI_IOCTL_GET_BUS_NUMBER:
	case SCSI_IOCTL_PROBE_HOST:
	case SG_GET_TRANSFORM:
	case SG_SCSI_RESET:
		if (atomic_read(&sdp->detaching))
			return -ENODEV;
		break;
	default:
		if (read_only)
			return -EPERM;	/* don't know so take safe approach */
		break;
	}

	result = scsi_ioctl_block_when_processing_errors(sdp->device,
			cmd_in, filp->f_flags & O_NDELAY);
	if (result)
		return result;
	return scsi_ioctl(sdp->device, cmd_in, p);
}

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.