From 6ba592fa014f21f35a8ee8da4ca7b95a018f13e8 Mon Sep 17 00:00:00 2001

From: Zheyu Ma <zheyuma97@gmail.com>

Date: Thu, 4 Aug 2022 20:41:25 +0800

Subject: video: fbdev: s3fb: Check the size of screen before memset_io()

Git-commit: 6ba592fa014f21f35a8ee8da4ca7b95a018f13e8

Patch-mainline: v6.0-rc1

References: bsc#1154048

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>

Acked-by: Thomas Zimmermann <tzimmermann@suse.de>

---

 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 b93c8eb02336..5069f6f67923 100644

--- a/drivers/video/fbdev/s3fb.c

+++ b/drivers/video/fbdev/s3fb.c

@@ -905,6 +905,8 @@ 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);

-- 

2.37.3