[PATCH 5.4 245/389] video: fbdev: vt8623fb: Check the size of screen before memset_io()

Greg Kroah-Hartman
2022-08-23T11:42:17Z

From: Zheyu Ma <zheyuma97@gmail.com>

[ Upstream commit ec0754c60217248fa77cc9005d66b2b55200ac06 ]

In the function vt8623fb_set_par(), the value of 'screen_size' is
calculated by the user input. If the user provides the improper value,
the value of 'screen_size' may larger than 'info->screen_size', which
may cause the following bug:

[ 583.339036] BUG: unable to handle page fault for address: ffffc90005000000
[ 583.339049] #PF: supervisor write access in kernel mode
[ 583.339052] #PF: error_code(0x0002) - not-present page
[ 583.339074] RIP: 0010:memset_orig+0x33/0xb0
[ 583.339110] Call Trace:
[ 583.339118] vt8623fb_set_par+0x11cd/0x21e0
[ 583.339146] fb_set_var+0x604/0xeb0
[ 583.339181] do_fb_ioctl+0x234/0x670
[ 583.339209] fb_ioctl+0xdd/0x130

Fix the this by checking the value of 'screen_size' before memset_io().

Fixes: 558b7bd86c32 ("vt8623fb: new framebuffer driver for VIA VT8623")
Signed-off-by: Zheyu Ma <zheyuma97@gmail.com>
Signed-off-by: Helge Deller <deller@gmx.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/video/fbdev/vt8623fb.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/drivers/video/fbdev/vt8623fb.c b/drivers/video/fbdev/vt8623fb.c
index c339a8fbad81..61e2028924a6 100644
--- a/drivers/video/fbdev/vt8623fb.c
+++ b/drivers/video/fbdev/vt8623fb.c
@@ -504,6 +504,8 @@ static int vt8623fb_set_par(struct fb_info *info)
(info->var.vmode & FB_VMODE_DOUBLE) ? 2 : 1, 1,
1, info->node);

+ if (screen_size > info->screen_size)
+ screen_size = info->screen_size;
memset_io(info->screen_base, 0x00, screen_size);

/* Device and screen back on */
--
2.35.1