net: phy: mdio-bcm-unimac: fix potential NULL dereference in unimac_mdio_probe()

CVE-2018-8043

platform_get_resource() may fail and return NULL, so we should
better check it's return value to avoid a NULL pointer dereference
a bit later in the code.

This is detected by Coccinelle semantic patch.

@@
expression pdev, res, n, t, e, e1, e2;
@@

res = platform_get_resource(pdev, t, n);
+ if (!res)
+   return -EINVAL;
... when != res == NULL
e = devm_ioremap(e1, res->start, e2);
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit 297a6961)
Signed-off-by: Po-Hsu Lin <po-hsu.lin@canonical.com>
Acked-by: Khaled Elmously <khalid.elmously@canonical.com>
Acked-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

drivers/net/phy/mdio-bcm-unimac.c

@@ -177,6 +177,8 @@ static int unimac_mdio_probe(struct platform_device *pdev)
 		return -ENOMEM;
 
 	r = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+	if (!r)
+		return -EINVAL;
 
 	/* Just ioremap, as this MDIO block is usually integrated into an
 	 * Ethernet MAC controller register range