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Date:   Tue, 16 Feb 2021 18:12:05 +0000
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     Ben Widawsky <ben.widawsky@intel.com>
Cc:     linux-cxl@vger.kernel.org, linux-acpi@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-nvdimm@lists.01.org,
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        Vishal Verma <vishal.l.verma@intel.com>,
        "John Groves (jgroves)" <jgroves@micron.com>,
        "Kelley, Sean V" <sean.v.kelley@intel.com>,
        kernel test robot <lkp@intel.com>
Subject: Re: [PATCH v4 4/9] cxl/mem: Add basic IOCTL interface
Message-ID: <YCwK9SblYCh/1lZS@zeniv-ca.linux.org.uk>
References: <20210216014538.268106-1-ben.widawsky@intel.com>
 <20210216014538.268106-5-ben.widawsky@intel.com>
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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.