[PATCH AUTOSEL 5.16 46/59] video: fbdev: sm712fb: Fix crash in smtcfb_write()

Sasha Levin
2022-03-30T12:00:33Z

From: Zheyu Ma <zheyuma97@gmail.com>

[ Upstream commit 4f01d09b2bbfbcb47b3eb305560a7f4857a32260 ]

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>
Signed-off-by: Helge Deller <deller@gmx.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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;
--
2.34.1