linux-kernel - Re: [PATCH v4 4/9] cxl/mem: Add basic IOCTL interface

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Message-ID: <YCwK9SblYCh/1lZS@zeniv-ca.linux.org.uk>
Date:   Tue, 16 Feb 2021 18:12:05 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Ben Widawsky <ben.widawsky@...el.com>
Cc:     linux-cxl@...r.kernel.org, linux-acpi@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-nvdimm@...ts.01.org,
        linux-pci@...r.kernel.org, Bjorn Helgaas <helgaas@...nel.org>,
        Chris Browy <cbrowy@...ry-design.com>,
        Christoph Hellwig <hch@...radead.org>,
        Dan Williams <dan.j.williams@...el.com>,
        David Hildenbrand <david@...hat.com>,
        David Rientjes <rientjes@...gle.com>,
        Ira Weiny <ira.weiny@...el.com>,
        Jon Masters <jcm@...masters.org>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Rafael Wysocki <rafael.j.wysocki@...el.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Vishal Verma <vishal.l.verma@...el.com>,
        "John Groves (jgroves)" <jgroves@...ron.com>,
        "Kelley, Sean V" <sean.v.kelley@...el.com>,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCH v4 4/9] cxl/mem: Add basic IOCTL interface

On Mon, Feb 15, 2021 at 05:45:33PM -0800, Ben Widawsky wrote:
> +	if (cmd->info.size_in) {
> +		mbox_cmd.payload_in = kvzalloc(cmd->info.size_in, GFP_KERNEL);
> +		if (!mbox_cmd.payload_in) {
> +			rc = -ENOMEM;
> +			goto out;
> +		}
> +
> +		if (copy_from_user(mbox_cmd.payload_in,
> +				   u64_to_user_ptr(in_payload),
> +				   cmd->info.size_in)) {
> +			rc = -EFAULT;
> +			goto out;
> +		}

Umm...  Do you need to open-code vmemdup_user()?  The only difference is
GFP_KERNEL allocation instead of GFP_USER one, and the latter is arguably
saner here...  Zeroing is definitely pointless - you either overwrite
the entire buffer with copy_from_user(), or you fail and free the damn
thing.