[PATCH] MFD: prevent null pointer dereference in mfd_add_device

[Florian Fainelli <florian@openwrt.org>]

If a driver calls mfd_add_device with a NULL argument for the mem_base resource
we will end up dereferencing it without checking for its validity here:
res[r].start = mem_base->start cell->resources[r].start; (line 53 of mfd-core.c)

This patch adds the checking on the mem_base argument and bails out accordingly
if it is NULL.

Signed-off-by: Florian Fainelli <florian@openwrt.org>
CC: stable@kernel.org
---
diff --git a/drivers/mfd/mfd-core.c b/drivers/mfd/mfd-core.c
index 8ffbb7a..f890b27 100644
--- a/drivers/mfd/mfd-core.c
+++ b/drivers/mfd/mfd-core.c
@@ -49,6 +49,8 @@ static int mfd_add_device(struct device *parent, int id,
 
 		/* Find out base to use */
 		if (cell->resources[r].flags & IORESOURCE_MEM) {
+			if (!mem_base)
+				goto fail_res;
 			res[r].parent = mem_base;
 			res[r].start = mem_base->start +
 				cell->resources[r].start;