Re: [PATCH] soc: aspeed: fix a ternary sign expansion bug

Patrick Venture
2021-04-22T14:56:41Z

On Thu, Apr 22, 2021 at 2:12 AM Dan Carpenter <dan.carpenter@oracle.com> wrote:
>
> The intent here was to return negative error codes but it actually
> returns positive values. The problem is that type promotion with
> ternary operations is quite complicated.
>
> "ret" is an int. "copied" is a u32. And the snoop_file_read() function
> returns long. What happens is that "ret" is cast to u32 and becomes
> positive then it's cast to long and it's still positive.
>
> Fix this by removing the ternary so that "ret" is type promoted directly
> to long.
>
> Fixes: 3772e5da4454 ("drivers/misc: Aspeed LPC snoop output using misc chardev")
> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Patrick Venture <venture@google.com>
> ---
> drivers/soc/aspeed/aspeed-lpc-snoop.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/soc/aspeed/aspeed-lpc-snoop.c b/drivers/soc/aspeed/aspeed-lpc-snoop.c
> index 210455efb321..eceeaf8dfbeb 100644
> --- a/drivers/soc/aspeed/aspeed-lpc-snoop.c
> +++ b/drivers/soc/aspeed/aspeed-lpc-snoop.c
> @@ -94,8 +94,10 @@ static ssize_t snoop_file_read(struct file *file, char __user *buffer,
> return -EINTR;
> }
> ret = kfifo_to_user(&chan->fifo, buffer, count, &copied);
> + if (ret)
> + return ret;
>
> - return ret ? ret : copied;
> + return copied;
> }
>
> static __poll_t snoop_file_poll(struct file *file,
> --
> 2.30.2
>