linux-kernel - [PATCH linux-next] video: fbdev: fbmem: fix pointer reference to null device field

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Date:   Thu, 10 Feb 2022 14:58:24 +0800
From:   Zhouyi Zhou <zhouzhouyi@...il.com>
To:     daniel@...ll.ch, deller@....de, sam@...nborg.org,
        linux@...ck-us.net, willy@...radead.org,
        linux-fbdev@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, paulmck@...nel.org,
        rcu@...r.kernel.org, pmenzel@...gen.mpg.de
Cc:     Zhouyi Zhou <zhouzhouyi@...il.com>
Subject: [PATCH linux-next] video: fbdev: fbmem: fix pointer reference to null device field

In function do_remove_conflicting_framebuffers, if device is NULL, there
will be null pointer reference. The patch add a check to the if expression.

Signed-off-by: Zhouyi Zhou <zhouzhouyi@...il.com>
---
Dear Linux folks

I discover this bug in the PowerPC VM provided by
Open source lab of Oregon State University:

https://lkml.org/lkml/2022/2/8/1145

I found that the root cause of null device field is in offb_init_fb:
info = framebuffer_alloc(sizeof(u32) * 16, NULL);

I have tested the patch in the PowerPC VM. Hope my patch can be correct.

Many Thanks
Zhouyi
--
 drivers/video/fbdev/core/fbmem.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
index 34d6bb1bf82e..422b1fc01722 100644
--- a/drivers/video/fbdev/core/fbmem.c
+++ b/drivers/video/fbdev/core/fbmem.c
@@ -1579,7 +1579,7 @@ static void do_remove_conflicting_framebuffers(struct apertures_struct *a,
 			 * If it's not a platform device, at least print a warning. A
 			 * fix would add code to remove the device from the system.
 			 */
-			if (dev_is_platform(device)) {
+			if (device && dev_is_platform(device)) {
 				registered_fb[i]->forced_out = true;
 				platform_device_unregister(to_platform_device(device));
 			} else {
-- 
2.25.1