linux-kernel - Re: [tpmdd-devel] [RFC PATCH 1/2] tee: generic TEE subsystem

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Message-ID: <20150417163054.GA28241@obsidianresearch.com>
Date:	Fri, 17 Apr 2015 10:30:54 -0600
From:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
To:	Jens Wiklander <jens.wiklander@...aro.org>
Cc:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	devicetree@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	javier@...igon.com, valentin.manea@...wei.com,
	emmanuel.michel@...com, Herbert Xu <herbert@...dor.apana.org.au>,
	jean-michel.delorme@...com, tpmdd-devel@...ts.sourceforge.net
Subject: Re: [tpmdd-devel] [RFC PATCH 1/2] tee: generic TEE subsystem

On Fri, Apr 17, 2015 at 09:50:56AM +0200, Jens Wiklander wrote:
> +	teedev = devm_kzalloc(dev, sizeof(*teedev), GFP_KERNEL);
[..]
> +	rc = misc_register(&teedev->miscdev);
[..]
> +void tee_unregister(struct tee_device *teedev)
> +{
[..]
> +	misc_deregister(&teedev->miscdev);
> +}
[..]
>+static int optee_remove(struct platform_device *pdev)
>+{
>+       tee_unregister(optee->teedev);

Isn't that a potential use after free? AFAIK misc_deregister does not
guarentee the miscdev will no longer be accessed after it returns, and
the devm will free it after optee_remove returns.

Memory backing a stuct device needs to be freed via the release
function.

We have been going through this for a while with TPM - it seems like
using misc devices dynamically is not a good idea. Manage your own
struct device directly..

Jason
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