int ipmi_si_mem_setup(struct si_sm_io *io)
{
	unsigned long addr = io->addr_data;
	int           mapsize, idx;

 	if (!addr)
 		return -ENODEV;
 
 	/*
 	 * Figure out the actual readb/readw/readl/etc routine to use based
 	 * upon the register size.
	 */
	switch (io->regsize) {
	case 1:
		io->inputb = intf_mem_inb;
		io->outputb = intf_mem_outb;
		break;
	case 2:
		io->inputb = intf_mem_inw;
		io->outputb = intf_mem_outw;
		break;
	case 4:
		io->inputb = intf_mem_inl;
		io->outputb = intf_mem_outl;
		break;
#ifdef readq
	case 8:
		io->inputb = mem_inq;
		io->outputb = mem_outq;
		break;
#endif
	default:
		dev_warn(io->dev, "Invalid register size: %d\n",
			 io->regsize);
		return -EINVAL;
	}

	/*
	 * Some BIOSes reserve disjoint memory regions in their ACPI
	 * tables.  This causes problems when trying to request the
	 * entire region.  Therefore we must request each register
	 * separately.
	 */
	for (idx = 0; idx < io->io_size; idx++) {
		if (request_mem_region(addr + idx * io->regspacing,
				       io->regsize, DEVICE_NAME) == NULL) {
			/* Undo allocations */
			mem_region_cleanup(io, idx);
			return -EIO;
		}
	}

	/*
	 * Calculate the total amount of memory to claim.  This is an
	 * unusual looking calculation, but it avoids claiming any
	 * more memory than it has to.  It will claim everything
	 * between the first address to the end of the last full
	 * register.
	 */
	mapsize = ((io->io_size * io->regspacing)
		   - (io->regspacing - io->regsize));
	io->addr = ioremap(addr, mapsize);
	if (io->addr == NULL) {
 		mem_region_cleanup(io, io->io_size);
 		return -EIO;
 	}

	io->io_cleanup = mem_cleanup;

 	return 0;
 }

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 Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.