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From:   Zheyu Ma <zheyuma97@gmail.com>
To:     deller@gmx.de, adaplas@gmail.com, santiago@crfreenet.org,
        akpm@linux-foundation.org
Cc:     linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org,
        linux-kernel@vger.kernel.org, Zheyu Ma <zheyuma97@gmail.com>
Subject: [PATCH 1/3] video: fbdev: vt8623fb: Check the size of screen before memset_io()
Date:   Thu,  4 Aug 2022 20:41:23 +0800
Message-Id: <20220804124125.3506755-2-zheyuma97@gmail.com>
In-Reply-To: <20220804124125.3506755-1-zheyuma97@gmail.com>
References: <20220804124125.3506755-1-zheyuma97@gmail.com>
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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>
---
 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 a92a8c670cf0..4274c6efb249 100644
--- a/drivers/video/fbdev/vt8623fb.c
+++ b/drivers/video/fbdev/vt8623fb.c
@@ -507,6 +507,8 @@ 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 */
-- 
2.25.1