Re: [PATCH] video: fbdev: sm712fb: Fix crash in smtcfb_write()

[Helge Deller]

On 3/2/22 15:33, Zheyu Ma wrote:
> 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@xxxxxxxxx>

Thanks... it's already in the fbdev git tree and queued up for v5.18...
https://git.kernel.org/pub/scm/linux/kernel/git/deller/linux-fbdev.git/commit/?h=for-next&id=bd771cf5c4254511cc4abb88f3dab3bd58bdf8e8

Helge


> ---
>  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;