static int tg3_phy_set_extloopbk(struct tg3 *tp)
{
	int err;
	u32 val;

	if (tp->phy_flags & TG3_PHYFLG_IS_FET)
		return 0;

	if ((tp->phy_id & TG3_PHY_ID_MASK) == TG3_PHY_ID_BCM5401) {
		/* Cannot do read-modify-write on 5401 */
		err = tg3_phy_auxctl_write(tp,
					   MII_TG3_AUXCTL_SHDWSEL_AUXCTL,
					   MII_TG3_AUXCTL_ACTL_EXTLOOPBK |
					   0x4c20);
		goto done;
	}

	err = tg3_phy_auxctl_read(tp,
				  MII_TG3_AUXCTL_SHDWSEL_AUXCTL, &val);
	if (err)
		return err;

	val |= MII_TG3_AUXCTL_ACTL_EXTLOOPBK;
	err = tg3_phy_auxctl_write(tp,
				   MII_TG3_AUXCTL_SHDWSEL_AUXCTL, val);

done:
	return err;
}

The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.