video: fbdev: vt8623fb: Check the size of screen before memset_io()

stable inclusion
from stable-v5.10.137
commit bd8269e57621e5b38cc0b4bd2fa02e85c9f2a441
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I60PLB

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=bd8269e57621e5b38cc0b4bd2fa02e85c9f2a441

--------------------------------

[ Upstream commit ec0754c6 ]

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: 558b7bd8 ("vt8623fb: new framebuffer driver for VIA VT8623")
Signed-off-by: NZheyu Ma <zheyuma97@gmail.com>
Signed-off-by: NHelge Deller <deller@gmx.de>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>
Reviewed-by: NWei Li <liwei391@huawei.com>

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 */