linux-kernel - [PATCH 4.14 148/229] video: fbdev: s3fb: Check the size of screen before memset

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Date:   Tue, 23 Aug 2022 10:25:09 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Zheyu Ma <zheyuma97@...il.com>,
        Helge Deller <deller@....de>, Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.14 148/229] video: fbdev: s3fb: Check the size of screen before memset_io()

From: Zheyu Ma <zheyuma97@...il.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@...il.com>
Signed-off-by: Helge Deller <deller@....de>
Signed-off-by: Sasha Levin <sashal@...nel.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 d63f23e26f7d..b17b806b4187 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