Re: [PATCH v3 20/23] fs: Allow copy_mount_options() to access user-space in a single pass

[Catalin Marinas <catalin.marinas@arm.com>]

On Tue, Apr 21, 2020 at 03:26:00PM +0100, Catalin Marinas wrote:
> --- a/fs/namespace.c
> +++ b/fs/namespace.c
> @@ -3025,13 +3025,16 @@ void *copy_mount_options(const void __user * data)
>  	if (!copy)
>  		return ERR_PTR(-ENOMEM);
>  
> -	size = PAGE_SIZE - offset_in_page(data);
> +	size = PAGE_SIZE;
> +	if (!arch_has_exact_copy_from_user(size))
> +		size -= offset_in_page(data);
>  
> -	if (copy_from_user(copy, data, size)) {
> +	if (copy_from_user(copy, data, size) == size) {
>  		kfree(copy);
>  		return ERR_PTR(-EFAULT);
>  	}
>  	if (size != PAGE_SIZE) {
> +		WARN_ON(1);
>  		if (copy_from_user(copy + size, data + size, PAGE_SIZE - size))
>  			memset(copy + size, 0, PAGE_SIZE - size);
>  	}

Argh, this WARN_ON should not be here at all. It's something I added to
make check that I don't reach this part in arm64. Will remove in v4.

-- 
Catalin