[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.wah...@i2se.com>

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.wah...@i2se.com>
Fixes: 71bad7f08641 ("staging: add bcm2708 vchiq driver")
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 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);