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From:   Zheyu Ma <zheyuma97@gmail.com>
To:     deller@gmx.de, sudipm.mukherjee@gmail.com,
        teddy.wang@siliconmotion.com
Cc:     linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org,
        linux-kernel@vger.kernel.org, Zheyu Ma <zheyuma97@gmail.com>
Subject: [PATCH] video: fbdev: sm712fb: Fix crash in smtcfb_write()
Date:   Wed,  2 Mar 2022 22:33:11 +0800
Message-Id: <20220302143311.2109322-1-zheyuma97@gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

When the sm712fb driver writes three bytes to the framebuffer, the
driver will crash:

    BUG: unable to handle page fault for address: ffffc90001ffffff
    RIP: 0010:smtcfb_write+0x454/0x5b0
    Call Trace:
     vfs_write+0x291/0xd60
     ? do_sys_openat2+0x27d/0x350
     ? __fget_light+0x54/0x340
     ksys_write+0xce/0x190
     do_syscall_64+0x43/0x90
     entry_SYSCALL_64_after_hwframe+0x44/0xae

Fix it by removing the open-coded endianness fixup-code.

Signed-off-by: Zheyu Ma <zheyuma97@gmail.com>
---
 drivers/video/fbdev/sm712fb.c | 21 ++++-----------------
 1 file changed, 4 insertions(+), 17 deletions(-)

diff --git a/drivers/video/fbdev/sm712fb.c b/drivers/video/fbdev/sm712fb.c
index 0dbc6bf8268a..e355089ac7d6 100644
--- a/drivers/video/fbdev/sm712fb.c
+++ b/drivers/video/fbdev/sm712fb.c
@@ -1130,7 +1130,7 @@ static ssize_t smtcfb_write(struct fb_info *info, const char __user *buf,
 		count = total_size - p;
 	}
 
-	buffer = kmalloc((count > PAGE_SIZE) ? PAGE_SIZE : count, GFP_KERNEL);
+	buffer = kmalloc(PAGE_SIZE, GFP_KERNEL);
 	if (!buffer)
 		return -ENOMEM;
 
@@ -1148,24 +1148,11 @@ static ssize_t smtcfb_write(struct fb_info *info, const char __user *buf,
 			break;
 		}
 
-		for (i = c >> 2; i--;) {
-			fb_writel(big_swap(*src), dst++);
+		for (i = (c + 3) >> 2; i--;) {
+			fb_writel(big_swap(*src), dst);
+			dst++;
 			src++;
 		}
-		if (c & 3) {
-			u8 *src8 = (u8 *)src;
-			u8 __iomem *dst8 = (u8 __iomem *)dst;
-
-			for (i = c & 3; i--;) {
-				if (i & 1) {
-					fb_writeb(*src8++, ++dst8);
-				} else {
-					fb_writeb(*src8++, --dst8);
-					dst8 += 2;
-				}
-			}
-			dst = (u32 __iomem *)dst8;
-		}
 
 		*ppos += c;
 		buf += c;
-- 
2.25.1