Re: [PATCH] evh_bytechan: fix out of bounds accesses

[Timur Tabi <timur@kernel.org>]

On Thu, Jan 9, 2020 at 1:41 AM Stephen Rothwell <sfr@canb.auug.org.au> wrote:
>
> ev_byte_channel_send() assumes that its third argument is a 16 byte array.
> Some places where it is called it may not be (or we can't easily tell
> if it is).  Newer compilers have started producing warnings about this,
> so make sure we actually pass a 16 byte array.

...

> +static unsigned int local_ev_byte_channel_send(unsigned int handle,
> +        unsigned int *count, const char *p)
> +{
> +       char buffer[EV_BYTE_CHANNEL_MAX_BYTES];
> +       unsigned int c = *count;
> +
> +       if (c < sizeof(buffer)) {
> +               memcpy(buffer, p, c);
> +               memset(&buffer[c], 0, sizeof(buffer) - c);
> +               p = buffer;
> +       }
> +       return ev_byte_channel_send(handle, count, p);
> +}

Why not simply correct the parameters of ev_byte_channel_send?

static inline unsigned int ev_byte_channel_send(unsigned int handle,
-unsigned int *count, const char buffer[EV_BYTE_CHANNEL_MAX_BYTES])
+unsigned int *count, const char *buffer)

Back then, I probably thought I was just being clever with this code,
but I realize now that it doesn't make sense to do the way I did.