Re: [PATCH v2 09/12] mini-os: use file_ops and get_file_from_fd() for console

[Andrew Cooper <amc96@xxxxxxxx>]

On 11/01/2022 15:12, Juergen Gross wrote:
> +static int savefile_write(int fd, const void *buf, size_t nbytes)
> +{
> +    int ret = 0, tot = nbytes;
> +    struct file *file = get_file_from_fd(fd);
> +
> +    while ( nbytes > 0 )
> +    {
> +        ret = xencons_ring_send(file->dev, (char *)buf, nbytes);
> +        nbytes -= ret;
> +        buf = (char *)buf + ret;
> +    }
> +
> +    return tot - nbytes;
> +}
> +
> +static int console_write(int fd, const void *buf, size_t nbytes)
> +{
> +    struct file *file = get_file_from_fd(fd);
> +
> +    console_print(file->dev, (char *)buf, nbytes);

I've just noticed this while committing the previous series, and I know
it is a preexisting bug, but the casts here are utterly unsafe, because
they're casting away constness.

console_print() is easy to fix, and just requires a prototype
adjustment.  That said, it also desperately also needs to fix 'int
length' to size_t to avoid problems with negative length VLAs on the stack.

xencons_ring_send() already takes const char *, so I'm pretty sure you
can just drop the casts here.  It too ought to not truncate size_t bytes
to "unsigned".

~Andrew