linux-kernel - Re: [PATCH v2] tpm: tpm_vtpm_proxy: fix a race condition in /dev/vtpmx creation

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Date:   Fri, 19 May 2023 18:00:39 -0400
From:   Stefan Berger <stefanb@...ux.ibm.com>
To:     Jarkko Sakkinen <jarkko@...nel.org>,
        linux-integrity@...r.kernel.org, Peter Huewe <peterhuewe@....de>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Stefan Berger <stefanb@...ux.vnet.ibm.com>
Cc:     Jarkko Sakkinen <jarkko.sakkinen@...i.fi>, stable@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] tpm: tpm_vtpm_proxy: fix a race condition in
 /dev/vtpmx creation



On 5/15/23 18:25, Jarkko Sakkinen wrote:
> From: Jarkko Sakkinen <jarkko.sakkinen@...i.fi>
> 
> /dev/vtpmx is made visible before 'workqueue' is initialized, which can
> lead to a memory corruption in the worst case scenario.
> 
> Address this by initializing 'workqueue' as the very first step of the
> driver initialization.
> 
> Cc: stable@...r.kernel.org
> Fixes: 6f99612e2500 ("tpm: Proxy driver for supporting multiple emulated TPMs")
> Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@...i.fi>
> ---
> v2:
> - Replace vtpmx_cleanup() with destroy_workqueue():
>    https://lore.kernel.org/linux-integrity/CSLCEYDKKWWE.36POIXVT65SLE@suppilovahvero/
> - Fix typo:
>    https://lore.kernel.org/linux-integrity/4651cf1c-423d-05c2-b4c3-9d829a2eadf4@linux.ibm.com/
> ---
>   drivers/char/tpm/tpm_vtpm_proxy.c | 30 +++++++-----------------------
>   1 file changed, 7 insertions(+), 23 deletions(-)
> 
> diff --git a/drivers/char/tpm/tpm_vtpm_proxy.c b/drivers/char/tpm/tpm_vtpm_proxy.c
> index 5c865987ba5c..30e953988cab 100644
> --- a/drivers/char/tpm/tpm_vtpm_proxy.c
> +++ b/drivers/char/tpm/tpm_vtpm_proxy.c
> @@ -683,37 +683,21 @@ static struct miscdevice vtpmx_miscdev = {
>   	.fops = &vtpmx_fops,
>   };
>   
> -static int vtpmx_init(void)
> -{
> -	return misc_register(&vtpmx_miscdev);
> -}
> -
> -static void vtpmx_cleanup(void)
> -{
> -	misc_deregister(&vtpmx_miscdev);
> -}
> -
>   static int __init vtpm_module_init(void)
>   {
>   	int rc;
>   
> -	rc = vtpmx_init();
> -	if (rc) {
> -		pr_err("couldn't create vtpmx device\n");
> -		return rc;
> -	}
> -
>   	workqueue = create_workqueue("tpm-vtpm");
>   	if (!workqueue) {
>   		pr_err("couldn't create workqueue\n");
> -		rc = -ENOMEM;
> -		goto err_vtpmx_cleanup;
> +		return -ENOMEM;
>   	}
>   
> -	return 0;
> -
> -err_vtpmx_cleanup:
> -	vtpmx_cleanup();
> +	rc = misc_register(&vtpmx_miscdev);
> +	if (rc) {
> +		pr_err("couldn't create vtpmx device\n");
> +		destroy_workqueue(workqueue);
> +	}
>   
>   	return rc;
>   }
> @@ -721,7 +705,7 @@ static int __init vtpm_module_init(void)
>   static void __exit vtpm_module_exit(void)
>   {
>   	destroy_workqueue(workqueue);
> -	vtpmx_cleanup();
> +	misc_deregister(&vtpmx_miscdev);
>   }
>   
>   module_init(vtpm_module_init);

Reviewed-by: Stefan Berger <stefanb@...ux.ibm.com>