[PATCH 4.9 039/105] staging: vchiq_2835_arm: Fix NULL ptr dereference in free_pagelist

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Stefan Wahren <stefan.wahren@xxxxxxxx>

commit 974d4d03fc020af4fa4e9e72a86f0fefa37803c5 upstream.

This fixes a NULL pointer dereference on RPi 2 with multi_v7_defconfig.
The function page_address() could return NULL with enabled CONFIG_HIGHMEM.
So fix this by using kmap() instead.

Signed-off-by: Stefan Wahren <stefan.wahren@xxxxxxxx>
Fixes: 71bad7f08641 ("staging: add bcm2708 vchiq driver")
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c
+++ b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c
@@ -538,18 +538,20 @@ free_pagelist(PAGELIST_T *pagelist, int
 			if (head_bytes > actual)
 				head_bytes = actual;
 
-			memcpy((char *)page_address(pages[0]) +
+			memcpy((char *)kmap(pages[0]) +
 				pagelist->offset,
 				fragments,
 				head_bytes);
+			kunmap(pages[0]);
 		}
 		if ((actual >= 0) && (head_bytes < actual) &&
 			(tail_bytes != 0)) {
-			memcpy((char *)page_address(pages[num_pages - 1]) +
+			memcpy((char *)kmap(pages[num_pages - 1]) +
 				((pagelist->offset + actual) &
 				(PAGE_SIZE - 1) & ~(g_cache_line_size - 1)),
 				fragments + g_cache_line_size,
 				tail_bytes);
+			kunmap(pages[num_pages - 1]);
 		}
 
 		down(&g_free_fragments_mutex);