Re: [PATCH] rust: firmware: return empty slice for zero-size firmware

["Onur Özkan" <work@onurozkan.dev>]

On Fri, 05 Jun 2026 09:13:55 +0100
Gary Guo <gary@garyguo.net> wrote:

> On Fri Jun 5, 2026 at 8:10 AM BST, Onur Özkan wrote:
> > On Thu, 04 Jun 2026 21:11:34 -0700
> > Yuan Tan <ytan089@ucr.edu> wrote:
> >
> >> Firmware::data() builds a Rust slice with core::slice::from_raw_parts().
> >> Unlike many C APIs, from_raw_parts() requires its pointer argument to be
> >> non-NULL even when the length is zero.
> >> 
> >> The firmware loader can represent an empty firmware image with size == 0
> >
> >
> > I haven't checked in detail yet but "empty firmware image with size == 0"
> > sounds like an invalid image. Can such an image actually make it all the way
> > to Firmware::data()? I would be surprised if the loader accepted it.
> 
> `kernel_read_file` will return EINVAL if file is of zero size. But I think the
> decompression path might produce this? The zstd code just does a
> 
>     out_buf = vzalloc(out_size);
> 
> which will trigger a WARN but still return NULL.

On NULL, it immediately fails with ENOMEM:

	out_buf = vzalloc(out_size);
	if (!out_buf)
		return -ENOMEM;

Thanks,
Onur

> 
> That said, I doubt any valid firmware will be just a compressed empty file.
> 
> Best,
> Gary