linux-kernel - Re: [PATCH v2] char: tpm: vtpm

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Date:   Fri, 9 Jul 2021 20:37:32 +0300
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Saubhik Mukherjee <saubhik.mukherjee@...il.com>
Cc:     peterhuewe@....de, jgg@...pe.ca, linux-integrity@...r.kernel.org,
        linux-kernel@...r.kernel.org, ldv-project@...uxtesting.org,
        andrianov@...ras.ru
Subject: Re: [PATCH v2] char: tpm: vtpm_proxy: Fix race in init

On Thu, Jul 08, 2021 at 03:22:59PM +0530, Saubhik Mukherjee wrote:
> vtpm_module_init calls vtpmx_init which calls misc_register. The file
> operations callbacks are registered. So, vtpmx_fops_ioctl can execute in
> parallel with rest of vtpm_module_init. vtpmx_fops_ioctl calls
> vtpmx_ioc_new_dev, which calls vtpm_proxy_create_device, which calls
> vtpm_proxy_work_start, which could read uninitialized workqueue.
> 
> To avoid this, create workqueue before vtpmx init.
> 
> Found by Linux Driver Verification project (linuxtesting.org).
> 
> Fixes: 6f99612e2500 ("tpm: Proxy driver for supporting multiple emulated TPMs")
> Signed-off-by: Saubhik Mukherjee <saubhik.mukherjee@...il.com>
> ---
> 
> Changes since v1 ([0]):
> - Add Fixes tag to commit message, as requested by Jarkko in [1].
> 
> [0]: https://lkml.org/lkml/2021/6/23/572
> [1]: https://lkml.org/lkml/2021/6/29/695
> 
>  drivers/char/tpm/tpm_vtpm_proxy.c | 19 +++++++++----------
>  1 file changed, 9 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/char/tpm/tpm_vtpm_proxy.c b/drivers/char/tpm/tpm_vtpm_proxy.c
> index 91c772e38bb5..225dfa026a8f 100644
> --- a/drivers/char/tpm/tpm_vtpm_proxy.c
> +++ b/drivers/char/tpm/tpm_vtpm_proxy.c
> @@ -697,23 +697,22 @@ 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;
> +	}
> +
> +	rc = vtpmx_init();
> +	if (rc) {
> +		pr_err("couldn't create vtpmx device\n");
> +		goto err_destroy_workqueue;
>  	}
>  
>  	return 0;
>  
> -err_vtpmx_cleanup:
> -	vtpmx_cleanup();
> +err_destroy_workqueue:
> +	destroy_workqueue(workqueue);
>  
>  	return rc;
>  }
> -- 
> 2.30.2
> 
> 

Thanks, I applied this.

Reviewed-by: Jarkko Sakkinen <jarkko@...nel.org>

/Jarkko