Re: [PATCH v2 11/16] fs: move permission hook out of do_iter_write()

[Christian Brauner <brauner@kernel.org>]

> -	ret = import_iovec(ITER_SOURCE, vec, vlen, ARRAY_SIZE(iovstack), &iov, &iter);
> -	if (ret >= 0) {
> -		file_start_write(file);
> -		ret = do_iter_write(file, &iter, pos, flags);
> -		file_end_write(file);
> -		kfree(iov);
> -	}
> +	if (!(file->f_mode & FMODE_WRITE))
> +		return -EBADF;
> +	if (!(file->f_mode & FMODE_CAN_WRITE))
> +		return -EINVAL;
> +
> +	ret = import_iovec(ITER_SOURCE, vec, vlen, ARRAY_SIZE(iovstack), &iov,
> +			   &iter);
> +	if (ret < 0)
> +		return ret;
> +
> +	tot_len = iov_iter_count(&iter);
> +	if (!tot_len)
> +		goto out;

Fwiw, the logic is slightly changed here. This now relies on
import_iovec() >= 0 then iov_iter_count() >= 0.

If that's ever changed and iov_iter_count() can return an error even
though import_iovec() succeeded we'll be returning the number of
imported bytes even though nothing was written and also generate a
fsnotify event because ret still points to the number of imported bytes.

The way it was written before it didn't matter because this was hidden
in a function call that returned 0 and initialized ret again. Anyway, I
can just massage that in-tree if that's worth it. Nothing to do for you.