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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Zheyu Ma <zheyuma97@gmail.com>,
        Helge Deller <deller@gmx.de>, Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.15 667/779] video: fbdev: arkfb: Check the size of screen before memset_io()
Date:   Mon, 15 Aug 2022 20:05:11 +0200
Message-Id: <20220815180405.850582198@linuxfoundation.org>
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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 d94cc5ad1ef6..8d092b106470 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