[PATCH 4.14 147/229] video: fbdev: arkfb: Check the size of screen before memset_io()

Greg Kroah-Hartman
2022-08-23T10:06:33Z

From: Zheyu Ma <zheyuma97@gmail.com>

[ Upstream commit 96b550971c65d54d64728d8ba973487878a06454 ]

In the function arkfb_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:

[ 659.399066] BUG: unable to handle page fault for address: ffffc90003000000
[ 659.399077] #PF: supervisor write access in kernel mode
[ 659.399079] #PF: error_code(0x0002) - not-present page
[ 659.399094] RIP: 0010:memset_orig+0x33/0xb0
[ 659.399116] Call Trace:
[ 659.399122] arkfb_set_par+0x143f/0x24c0
[ 659.399130] fb_set_var+0x604/0xeb0
[ 659.399161] do_fb_ioctl+0x234/0x670
[ 659.399189] fb_ioctl+0xdd/0x130

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

Fixes: 681e14730c73 ("arkfb: new framebuffer driver for ARK Logic cards")
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/arkfb.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/drivers/video/fbdev/arkfb.c b/drivers/video/fbdev/arkfb.c
index bfa221b68d71..f7920987dd24 100644
--- a/drivers/video/fbdev/arkfb.c
+++ b/drivers/video/fbdev/arkfb.c
@@ -794,6 +794,8 @@ static int arkfb_set_par(struct fb_info *info)
value = ((value * hmul / hdiv) / 8) - 5;
vga_wcrt(par->state.vgabase, 0x42, (value + 1) / 2);

+ if (screen_size > info->screen_size)
+ screen_size = info->screen_size;
memset_io(info->screen_base, 0x00, screen_size);
/* Device and screen back on */
svga_wcrt_mask(par->state.vgabase, 0x17, 0x80, 0x80);
--
2.35.1