Re: [PATCH] fbcon: Fix a NULL pointer dereference issue in fbcon_putcs

From: Helge Deller
Date: Tue Sep 17 2024 - 02:25:39 EST


On 9/16/24 03:10, Qianqiang Liu wrote:
syzbot has found a NULL pointer dereference bug in fbcon [1].

This issue is caused by ops->putcs being a NULL pointer.
We need to check the pointer before using it.

[1] https://syzkaller.appspot.com/bug?extid=3d613ae53c031502687a

Cc: stable@xxxxxxxxxxxxxxx
Reported-and-tested-by: syzbot+3d613ae53c031502687a@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Qianqiang Liu <qianqiang.liu@xxxxxxx>
---
drivers/video/fbdev/core/fbcon.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
index 3f7333dca508..96c1262cc981 100644
--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c
@@ -1284,7 +1284,7 @@ static void fbcon_putcs(struct vc_data *vc, const u16 *s, unsigned int count,
struct fbcon_display *p = &fb_display[vc->vc_num];
struct fbcon_ops *ops = info->fbcon_par;

- if (!fbcon_is_inactive(vc, info))
+ if (!fbcon_is_inactive(vc, info) && ops->putcs)

I think this patch just hides the real problem.
How could putcs have become NULL ?

Helge

ops->putcs(vc, info, s, count, real_y(p, ypos), xpos,
get_color(vc, info, scr_readw(s), 1),
get_color(vc, info, scr_readw(s), 0));