r8169: checks against wrong mac addresse init

Checking the signature of the eeprom and the validity of the
MAC address should be enough to filter out the bad addresses
observed so far.

Contributed by Ivan Vecera and Martin Capitanio.

Tested on 8102el, 8168b and 8169 for a start.
Signed-off-by: Francois Romieu <romieu@fr.zoreil.com>
Cc: Edward Hsu <edward_hsu@realtek.com.tw>

drivers/net/r8169.c

@@ -81,6 +81,10 @@ static const int multicast_filter_limit = 32;
 #define RTL8169_TX_TIMEOUT	(6*HZ)
 #define RTL8169_PHY_TIMEOUT	(10*HZ)
 
+#define RTL_EEPROM_SIG		cpu_to_le32(0x8129)
+#define RTL_EEPROM_SIG_MASK	cpu_to_le32(0xffff)
+#define RTL_EEPROM_SIG_ADDR	0x0000
+
 /* write/read MMIO register */
 #define RTL_W8(reg, val8)	writeb ((val8), ioaddr + (reg))
 #define RTL_W16(reg, val16)	writew ((val16), ioaddr + (reg))
@@ -1944,9 +1948,10 @@ static void rtl_init_mac_address(struct rtl8169_private *tp,
 				 void __iomem *ioaddr)
 {
 	struct pci_dev *pdev = tp->pci_dev;
-	u8 cfg1;
 	int vpd_cap;
+	__le32 sig;
 	u8 mac[8];
+	u8 cfg1;
 
 	cfg1 = RTL_R8(Config1);
 	if (!(cfg1  & VPD)) {
@@ -1961,7 +1966,16 @@ static void rtl_init_mac_address(struct rtl8169_private *tp,
 	if (!vpd_cap)
 		return;
 
-	/* MAC address is stored in EEPROM at offset 0x0e
+	if (rtl_eeprom_read(pdev, vpd_cap, RTL_EEPROM_SIG_ADDR, &sig) < 0)
+		return;
+
+	if ((sig & RTL_EEPROM_SIG_MASK) != RTL_EEPROM_SIG) {
+		dev_info(&pdev->dev, "Missing EEPROM signature: %08x\n", sig);
+		return;
+	}
+
+	/*
+	 * MAC address is stored in EEPROM at offset 0x0e
 	 * Realtek says: "The VPD address does not have to be a DWORD-aligned
 	 * address as defined in the PCI 2.2 Specifications, but the VPD data
 	 * is always consecutive 4-byte data starting from the VPD address
@@ -1983,8 +1997,8 @@ static void rtl_init_mac_address(struct rtl8169_private *tp,
 			 print_mac(buf, mac));
 	}
 
-	/* Write MAC address */
-	rtl_rar_set(tp, mac);
+	if (is_valid_ether_addr(mac))
+		rtl_rar_set(tp, mac);
 }
 
 static int __devinit