Re: [PATCH v1 1/4] lib: introduce copy_struct_from_user() helper

[Linus Torvalds]

On Wed, Sep 25, 2019 at 10:00 AM Aleksa Sarai <cyphar@xxxxxxxxxx> wrote:
>
> +int is_zeroed_user(const void __user *from, size_t size)

I like how you've done this, but it's buggy and only works on 64-bit.

All the "u64" and "8" cases need to be "unsigned long" and
"sizeof(unsigned long)".

Part of that requirement is:

> +               unsafe_get_user(val, (u64 __user *) from, err_fault);

This part works fine - although 64-bit accesses migth be much more
expensive and the win of unrolling might not be sufficient - but:

> +               if (align) {
> +                       /* @from is unaligned. */
> +                       val &= ~aligned_byte_mask(align);
> +                       align = 0;
> +               }

This part fundamentally only works on 'unsigned long'.

         Linus