[PATCH 5.4 247/389] video: fbdev: s3fb: Check the size of screen before memset_io()

Greg Kroah-Hartman
2022-08-23T11:42:26Z

From: Zheyu Ma <zheyuma97@gmail.com>

[ Upstream commit 6ba592fa014f21f35a8ee8da4ca7b95a018f13e8 ]

In the function s3fb_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:

[ 54.083733] BUG: unable to handle page fault for address: ffffc90003000000
[ 54.083742] #PF: supervisor write access in kernel mode
[ 54.083744] #PF: error_code(0x0002) - not-present page
[ 54.083760] RIP: 0010:memset_orig+0x33/0xb0
[ 54.083782] Call Trace:
[ 54.083788] s3fb_set_par+0x1ec6/0x4040
[ 54.083806] fb_set_var+0x604/0xeb0
[ 54.083836] do_fb_ioctl+0x234/0x670

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

Fixes: a268422de8bf ("fbdev driver for S3 Trio/Virge")
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/s3fb.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/drivers/video/fbdev/s3fb.c b/drivers/video/fbdev/s3fb.c
index be16c349c10f..228e5ee7a547 100644
--- a/drivers/video/fbdev/s3fb.c
+++ b/drivers/video/fbdev/s3fb.c
@@ -902,6 +902,8 @@ static int s3fb_set_par(struct fb_info *info)
value = clamp((htotal + hsstart + 1) / 2 + 2, hsstart + 4, htotal + 1);
svga_wcrt_multi(par->state.vgabase, s3_dtpc_regs, value);

+ 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