Re: [PATCH RFC 3/8] openat2: explicitly return -E2BIG for (usize > PAGE_SIZE)

[Arnd Bergmann]

On Mon, Sep 2, 2024, at 07:06, Aleksa Sarai wrote:
> While we do currently return -EFAULT in this case, it seems prudent to
> follow the behaviour of other syscalls like clone3. It seems quite
> unlikely that anyone depends on this error code being EFAULT, but we can
> always revert this if it turns out to be an issue.

Right, it's probably a good idea to have a limit there rather than
having a busy loop with a user-provided length when the only bound is
the available virtual memory.

>  	if (unlikely(usize < OPEN_HOW_SIZE_VER0))
>  		return -EINVAL;
> +	if (unlikely(usize > PAGE_SIZE))
> +		return -E2BIG;
> 

Is PAGE_SIZE significant here? If there is a need to enforce a limit,
I would expect this to be the same regardless of kernel configuration,
since the structure layout is also independent of the configuration.

Where is the current -EFAULT for users passing more than a page?
I only see it for reads beyond the VMA, but not e.g. when checking
terabytes of zero pages from an anonymous mapping.

    Arnd